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Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion

BRADLEY C. LIVEZEY, RICHARD L. ZUSI

Zoological Journal of the Linnean Society · 2007

doi:10.1111/j.1096-3642.2006.00293.x

Abstract

In recent years, avian systematics has been characterized by a diminished reliance on morphological cladistics of modern taxa, intensive palaeornithogical research stimulated by new discoveries and an inundation by analyses based on DNA sequences. Unfortunately, in contrast to significant insights into basal origins, the broad picture of neornithine phylogeny remains largely unresolved. Morphological studies have emphasized characters of use in palaeontological contexts. Molecular studies, following disillusionment with the pioneering, but non-cladistic, work of Sibley and Ahlquist, have differed markedly from each other and from morphological works in both methods and findings. Consequently, at the turn of the millennium, points of robust agreement among schools concerning higher-order neornithine phylogeny have been limited to the two basalmost and several mid-level, primary groups. This paper describes a phylogenetic (cladistic) analysis of 150 taxa of Neornithes, including exemplars from all non-passeriform families, and subordinal representatives of Passeriformes. Thirty-five outgroup taxa encompassing Crocodylia, predominately theropod Dinosauria, and selected Mesozoic birds were used to root the trees. Based on study of specimens and the literature, 2954 morphological characters were defined; these characters have been described in a companion work, approximately one-third of which were multistate (i.e. comprised at least three states), and states within more than one-half of these multistate characters were ordered for analysis. Complete heuristic searches using 10 000 random-addition replicates recovered a total solution set of 97 well-resolved, most-parsimonious trees (MPTs). The set of MPTs was confirmed by an expanded heuristic search based on 10 000 random-addition replicates and a full ratchet-augmented exploration to ascertain global optima. A strict consensus tree of MPTs included only six trichotomies, i.e. nodes differing topologically among MPTs. Bootstrapping (based on 10 000 replicates) percentages and ratchet-minimized support (Bremer) indices indicated most nodes to be robust. Several fossil Neornithes (e.g. Dinornithiformes, Aepyornithiformes) were placed within the ingroup a posteriori either through unconstrained, heursitic searches based on the complete matrix augmented by these taxa separately or using backbone-constraints. Analysis confirmed the topology among outgroup Theropoda and achieved robust resolution at virtually all levels of the Neornithes. Findings included monophyly of the palaeognathous birds, comprising the sister taxa Tinamiformes and ratites, respectively, and the Anseriformes and Galliformes as monophyletic sister-groups, together forming the sister-group to other Neornithes exclusive of the Palaeognathae (Neoaves). Noteworthy inferences include: (i) the sister-group to remaining Neoaves comprises a diversity of marine and wading birds; (ii) Podicipedidae are the sister-group of Gaviidae, and not closely related to the Phoenicopteridae, as recently suggested; (iii) the traditional Pelecaniformes, including the shoebill (Balaeniceps rex) as sister-taxon to other members, are monophyletic; (iv) traditional Ciconiiformes are monophyletic; (v) Strigiformes and Falconiformes are sister-groups; (vi) Cathartidae is the sister-group of the remaining Falconiformes; (vii) Ralliformes (Rallidae and Heliornithidae) are the sister-group to the monophyletic Charadriiformes, with the traditionally composed Gruiformes and Turniciformes (Turnicidae and Mesitornithidae) sequentially paraphyletic to the entire foregoing clade; (viii) Opisthocomus hoazin is the sister-taxon to the Cuculiformes (including the Musophagidae); (ix) traditional Caprimulgiformes are monophyletic and the sister-group of the Apodiformes; (x) Trogoniformes are the sister-group of Coliiformes; (xi) Coraciiformes, Piciformes and Passeriformes are mutually monophyletic and closely related; and (xii) the Galbulae are retained within the Piciformes. Unresolved portions of the Neornithes (nodes having more than one most-parsimonious solution) comprised three parts of the tree: (a) several interfamilial nodes within the Charadriiformes; (b) a trichotomy comprising the (i) Psittaciformes, (ii) Columbiformes and (iii) Trogonomorphae (Trogoniformes, Coliiformes) + Passerimorphae (Coraciiformes, Piciformes, Passeriformes); and (c) a trichotomy comprising the Coraciiformes, Piciformes and Passeriformes. The remaining polytomies were among outgroups, although several of the highest-order nodes were only marginally supported; however, the majority of nodes were resolved and met or surpassed conventional standards of support. Quantitative comparisons with alternative hypotheses, examination of highly supportive and diagnostic characters for higher taxa, correspondences with prior studies, complementarity and philosophical differences with palaeontological phylogenetics, promises and challenges of palaeogeography and calibration of evolutionary rates of birds, and classes of promising evidence and future directions of study are reviewed. Homology, as applied to avian examples of apparent homologues, is considered in terms of recent theory, and a revised annotated classification of higher-order taxa of Neornithes and other closely related Theropoda is proposed. (c) 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 149, 1-95.

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Full text

From PubMed Central, U.S. National Library of Medicine, as current on Oct 19, 2026. Paragraph numbers are ours, so an answer can point at one.

INTRODUCTION

‘But as far as the problem of the relationship of the orders of birds is concerned, so many distinguished investigators have labored in this field in vain, that little hope is left for spectacular break-throughs.’ (: 277)

‘It must be remembered that the basic avian structure was determined at an early stage in the evolutionary history of birds because of the rigorous limitations placed upon a flying vertebrate. Consequently, adaptations in the birds have been along lines that are not always indicated by the details of anatomy, a fact that makes these vertebrates highly interesting to the student of recent animals but difficult subjects for the palaeontologist.’ (: 187)

Confines of tradition

The opening quotation from ) clearly articulates a fundamental assumption of functional constraint under which many avian systematists laboured for more than a century. Apparently retarded rates of morphological and molecular change strongly influenced evolutionary theory as applied to birds, e.g. prompting assessment of phylogenetic principles for morphologically ‘uniform’ groups. This duality – higher-order diversity defying phylogenetic inference and study of morphological variation lacking unified phylogenetic focus – was influential during the last century.

Avian systematics has followed a general tri-phasic pattern: (i) a descriptive period – epitomized by the landmark works by ), ) and, ), in which early classifications of the period were based solely on anatomical evidence and distinctly informal in nature; (ii) a comparative (multitaxic) period – typically confined to single skeletal elements, articulations, limbs or organ systems (e.g.,,;; ); and (iii) a phylogenetic period – the primary literature considered herein.

Important advances in avian systematics have been typified by studies focused on key extant taxa – e.g. Balaeniceps rex and Pedionomus torquatus – or promising aspects of anatomy – e.g. appendicular myology – as well as a few broad surveys of modern taxa. Regardless of method, however, scale of avian phylogenetics seldom exceeded single orders prior to 1990, when palaeontological finds revived such broad systematic endeavours. From the earliest years of avian systematics, ornithologists were attracted to taxa posing confusing combinations of characters, and a few systematists showed an uncanny recognition of taxa that were key to problems concerning larger groups (Table 1).

Percy Roycroft Lowe (British Museum), despite an idiosyncratic view of ontogeny in evolution and pre-Hennigian concepts of phylogenetic reconstruction, undertook early and under-appreciated attempts to resolve the phylogenetic positions of problematic avian groups. Early works by Lowe emphasized the vexing Charadriiformes and allied Gruiformes, the ratites, ‘primitive’ characters of Sphenisciformes, characters of Archaeopteryx possibly germane to an alliance between birds and dinosaurs, the perplexingly apomorphic Apodiformes, and preliminary diagnoses for Cuculiformes, Piciformes and Coraciiformes. Intermittently during the same period, Lowe also considered possible relationships among ratites and some non-avian Theropoda, e.g. Struthiomimus and Ornitholestes, although he was hampered by the prevailing confusion between synapomorphy and symplesiomorphy and their respective implications for phylogeny. René Verheyen (Institut Royale Belgique) authored approximately 35 papers during 1950–60 that centred on problems of avian systematics by means of semi-quantitative methods (e.g.,,,, ). The work by Verheyen, however, was deemed idiosyncratic and largely ignored.

,, ) chronicled avian systematics since the late 18th century. ) reviewed the philosophical underpinnings of avian systematics in recent decades, and clarified for the time the fundamental differences among various systematic schools. Avian systematics in the late 20th century has been marked by a trough in morphological phylogenetics and a concomitant peak in molecular systematics. The pessimism expressed by ) regarding the phylogenetic potential of morphological characters, however, contrasts with surveys of the contributions of both. ) concluded that considerable congruence existed among reconstructions based on DNA–DNA hybridization, sequence-based analyses, and comparative morphology. In a survey of the history of avian molecular systematics, ) recounted discrepancies between reconstructions of basal lineages based on mtDNA and nuclear genes. As discourse among schools increased, it was evident that the familiar demons of avian systematics haunted both morphological and molecular practices: differential selection and adaptation, convergence, extinction of lineages, challenges of homology and alignment, and heterogeneity of evolutionary rates and branch-lengths.

Palaeontological contributions

Fossils essentially are amenable only to morphological study, with the exception of a few, fortunate recoveries of ‘ancient DNA’, and typically provide only substandard anatomical material or incomplete specimens. Some of the most intense conflicts among avian systematists stemmed either from a commitment to phenetics or the idiosyncracies of palaeornithological perspectives (e.g.,,; ). Influential for avian systematics was the view that avian fossils are both fragile and correspondingly rare, despite compendia indicative of extensive taxonomic diversity. Deficiencies in the fossil record and challenges of homology (e.g. ), however, did not diminish a reliance on new fossils to resolve the broad outlines of avian evolution.

Palaeontological contributions have been confounded by speculative evolutionary scenarios that extend beyond the underlying systematics. The purported issue of ‘fossil mosaics’ – a predictable consequence of heterogeneity in evolutionary rates among characters – further exacerbated the interpretation of evolutionary change.: 291) concluded that during the 150 years of avian palaeontology, ‘… a major burden for palaeornithologists has been a lack of comparative skeletons of recent birds’, and that the ‘other major problem is the incompleteness of most avian fossils.’ With the latter we agree, but the former is less a problem of availability than the result of under-utilization, a factor worsened by the rush to a molecular era.

Ethological and parasitological phylogenetics

Behavioural characters are only infrequently used in formal cladistic analyses (e.g.;;,;; ), or precursors thereof. Complete designs have not been attempted for lack of comparable data for species of interest, and some are limited to assessments a posteriori for phylogenetic signal. Phylogeneticists have come to consider selected ethological traits – notably displays of courtship – worthy of phylogenetic interpretation. Patterns of interspecific hybridization have perhaps the longest history of study, notably among Anseriformes. Eventually, interfertility was recognized to be plesiomorphic and comparatively conservative, and therefore interspecific hybridization to be uniformative with respect to phylogenetics. Similarly, phylogenetics of ectoparasites has been explored only infrequently in phylogenetic reconstructions of birds. Consequently, the two primary sources of phylogenetic signal for birds during the 20th century have been morphological variation and molecular (increasingly DNA sequence) data.

Molecular phylogenetics

Following an implicit rejection of DNA hybridization on the grounds of its phenetic nature and woefully incomplete distance matrices, molecular systematics focused on the cladistics of parsimony or increasingly explored the probabilistics of maximum-likelihood and Bayesian methods. Phylogenetic analyses based solely on mitochondrial genes de jour (e.g. cyt b, 12S) initially were accorded considerable validity, but these works effectively were trumped by those based on entire mitochondrial genomes or including nuclear genes, with few exceptions. Similarly, explorations of very limited numbers of genes were eclipsed by expanded analyses of nuclear data with diversified taxonomic samples. This progression of analytical refinements and expanded taxonomic representation, despite the continued challenges discovered in each (e.g. ), is likely to continue and perhaps accelerate with the implementation of studies based on ‘total evidence’.

Current status of avian phylogenetics

‘… the currently accepted arrangement of birds in no way reflects the probable evolutionary history of the class…. The arrangement used here is predicated mainly on the assumptions that birds originated on land rather than in the water, and that highly specialized waterbirds are more derived than less specialized ones…. a consensus has emerged that birds originated, if not in trees, certainly on land. Therefore, we should look for the most primitive taxa among the land birds.’ (: 83, 84)

‘If one had to summarize the current state of knowledge, the most pessimistic view would see the neoavian tree as a “comb,” with little or no resolution among most traditional families and orders.’ (: 475)

‘Perhaps the greatest unsolved problem in avian systematics is the evolutionary relationships among modern higher-level taxa.’ (: 1052)

: 974) concluded: ‘It is almost an offense against birds that the deep mammalian tree is virtually resolved … whilst there are still major uncertainties about many aspects of the avian evolutionary tree.’ In support of this sentiment, the authors cited fundamental discordance among phylogenetic inferences for birds based on mitochondrial and nuclear genomes, an assessment at odds with a contemporary review by ). Discussion of morphological efforts by ) was limited to the uncertainties raised by, ) but verified increasingly by analyses. Reconstructions of the higher-order relationships of birds based on morphological characters, in turn, have been depauperate in both characters and taxa and seldom genuinely cladistic (e.g.,,;; ).

Regardless of the taxonomic group considered, however, the sobering truth is that the goal of phylogenetics is extremely ambitious and without easy or uniformly reliable means of accomplishment. It is beyond debate that the conceptual framework of morphological cladistics and ever-increasing computational power has led to significant progress. Nevertheless, it is also clear that many phylogenetic problems have proven resistant to all attempts at solution and seem destined to controversy. Also, phylogenetic endeavours are replete with disagreements in method (both for reconstruction and for evaluation of estimates) and types of evidence considered most reliable. Currently, the tendency is to consider molecular reconstructions as representing the future of avian phylogenetics, and that it is simply a matter of time, perhaps less than a decade, before a global consensus is achieved within the systematic community.

Deficiencies in taxa or characters typically render comparisons among investigations problematic, and attempts to reconcile the phylogenetic evidence for Aves substantiate this generality. Indicative of disappointing progress in mid- and lower-order avian phylogenetics is the conclusion that basal (higher-order) nodes may be irresolvable or accurate approximations of genuine, explosive radiations. While demonstrably true of analyses confined to few characters or limited taxonomically, a single decade of uninspiring inference is insufficient to judge solution to be beyond hope.

The current status of molecular resolution of deepest neornithine nodes, however, serves to underline the likelihood that many genes provide inadequate phylogenetic signal for the problems at hand, a deficiency exacerbated by basal polarities necessarily based on closest extant relatives that are unfortunately comparatively distantly related, e.g. Crocodylia and Testudines. The fact that ‘nearest’ outgroup(s) for molecular analysis need to be be extant has had unfortunate implications for rooting, in that for Neornithes these outgroups are comparatively distantly related and may converge on ‘white noise’ as indicators of avian polarities, especially for rapidly evolving mitochondrial data.

Like morphological estimates, a number of potential pitfalls (rooting aside) afflict molecular reconstructions, e.g. serial homoplasy by misalignment, distortions related to silent substitutions, unrealistic treatment of ‘gaps’, and unequal evolutionary rates over extended intervals of geological time and among lineages. Furthermore, disagreement persists if not expands regarding methodological preferences – e.g. classes of data employed, protocols for alignment (i.e. diagnosis of serial homology), choice among reconstructive methods, and assessment of resolution and support. Until substantial agreement concerning methods is attained and accurate synergism among molecular and morphological methods secured, the field will remain vulnerable to methodological bias and a tolerance for poorly supported hypotheses of phylogeny, in which even the best-supported works disagree significantly (see Figs 4–9).

Goals and objectives

The primary purpose of this paper is to present a morphologically based phylogenetic hypothesis of higher-order relationships of Neornithes. A compendium of characters is provided within the companion work, including a bibliographic synthesis, annotations of prior uses of synonymous and related characters, and a compact disc of the data matrix for refinement and augmentation. The secondary objective of this work is to provide a cladistic alternative to the molecular phenetics of ), at least for non-passeriform families, and to serve as a framework for lower-level studies of included families. An earlier paper on philosophical and methodogical issues, despite an explicit disclaimer to the contrary, frequently has been cited as a phylogenetic hypothesis appropriate for comparison with works considered complete by their authors, even regarding positions of individual taxa (e.g. ). We began the present study with the opinion that the phylogenetic signal encoded within avian anatomy is, with adequate study of both definitive and ontogenetic variation of an adequate sample of modern lineages, more than sufficient for the reconstruction of the higher-order phylogeny of Neornithes. We remain at least as optimistic concerning this goal.

The present phylogenetic hypothesis is intended to serve both as a baseline estimate and ‘scaffold’ for finer-scale reconstructions of terminal clades (i.e. families), as attempts at broad reconstructions of the phylogeny of Neornithes to date have been limited, at the very least, in taxonomic representation (e.g. ) or discredited methods of inference. We also sought to provide robust nodes supplemental to the few phylogenetic hypothesis currently employed for calibrations of age based on fossils (e.g.; ) or their surrogates. Integration of these data with a rich matrix of DNA-sequence data is planned to explore the power of ‘total evidence’ to recover both higher-level and lower-level avian phylogeny. Perhaps most importantly for the facilitation of future analyses, be these morphological or molecular, is the identification of sister-groups (optimal outgroups) for purposes of rooting analyses of single orders or families. The comparatively sparse representation of taxa in the present analysis reflected logistical limits, but was considered adequate for achieving the stated objectives. Findings herein principally were compared with modern higher-order reconstructions (e.g.;; ), the most critical of which are summarized graphically here (Figs 1–9). Works of narrower scope are considered where issues of familial monophyly persist, with emphasis on truly phylogenetic works as opposed to eclectic or phenetic assessments.

Taxonomic sampling and exemplars

Taxonomic diversity generally represents a much greater logistical burden than diversity of characters in phylogenetic analyses, and challenges imposed by taxa can be exacerbated by unfortunate sampling. However, it has been demonstrated that density of taxonomic sampling for the ingroup varies directly with expected accuracy, support and resolution of resultant trees, although the importance of taxonomic density appears to be greatest for sequence data (especially with respect to long-branch attraction). Expectations of resolution and accuracy that are related to richness of morphological characters, unlike for sequence data, have not been subjected to numerical assessment, but logically are significantly related. The importance of monophyly of the groups represented by exemplars prompted the citation, where available, of analyses germane to the monophyly and content of taxonomic families represented here by exemplars.

We sought to maximize richness of characters and represent higher-order taxa within logistic limits that: (i) represented (sub)familial diversity among non-passeriform Neornithes; (ii) provided special insights into interfamilial groups; (iii) were suitably represented by essential specimens; and (iv) included taxa of special interest to avian systematics. Neornithine families were represented by one or more exemplars deemed in most cases to reflect at least a ‘basal’ member (i.e. candidate sister-taxon of other members) of the taxon in question. This method is not without difficulties, as concerns persist regarding the use of exemplars as terminal surrogates for higher-order taxa, notably where polymorphism is involved or monophyly of terminals represented by single exemplars is in question. Also, limitations on specimens of specialized preparations impose critical deficiences on resultant data matrices, an abiding concern of anatomical collections of birds. Relatively strong support for monophyly of most clades alleviated concerns regarding taxonomic sampling, especially given the number of morphological characters employed. However, use of minimal numbers of exemplars justifies caution in the diagnostics given for diverse orders and families herein (Table 2).

Crocodylia and non-avian theropod Dinosauria served as ‘ultra-deep’ and primary outgroups, respectively, to root Neornithes, but the inclusion of most published characters in placing these taxa chronicled the acquisition of avian characters during the Mesozoic. The recent extension of avian roots, both by newly discovered avialian taxa and confirmation of early roots among non-avian theropods, circumvented difficulties of establishing basal polarities for Neornithes based on inadequate diversity of Mesozoic relatives or (for narrower reconstructions) or dubious reliance on the problematic Palaeognathae, notably caused by the complex of apomorphy and plesiomorphy of ratites relative to the Tinaniformes. These outgroups optimized rooting by the hierarchy of information afforded by multiple (nested) outgroups and avoided the analytical problems implicit with hypothetical ancestors.

Four comparatively distant outgroups were sampled for estimating deep polarities – non-Archosauromorpha (informative states of comparable characters at the approximate origin of the archosaurian clade), Crocodylomorpha (i.e. non-dinosaurian Archosauria), Ornithischia (i.e. non-saurischian Dinosauria) and Sauropodomorpha (modalities of non-theropod Saurischia). Among non-avian Theropoda, Herrerasaurus served as the most informative of the generic outgroups. Groupings among outgroups (i.e. among non-avian taxa) were of only secondary interest, however, whereas establishment of a realiable root for the Neornithes was the principal priority.

Indeterminate and redundant contributions of some outgroup taxa with respect to the primary objective of this analysis, as well as excessive proportions of missing data recognized upon completion of the data matrix, prompted limited pruning and merging of taxa (primarily outgroups) for analysis: (a) taxa pruned –Euparkeria, Syntarsus, Eoraptor, Saurornitholestes, ‘Caenognathidae’, Microvenator, Citipati, Chironestes, Ornitholestes, Segnosaurus, Avimimus, Sinornithosaurus, Microraptor, Erlicosaurus, Shuvuuia, Jehelornis, Gobipteryx, Patagopteryx; Diatrymiformes, Dromornithiformes, Sylviornis; (b) taxa merged: {Allosaurus, Sinraptor}∼ Allosauroidea; {Tyrannosaurus, Albertosaurus}∼ Tyrannosauridae; {Sinovenator, Sinornithoides, Troodon}∼Troodontidae; {‘Enantiornithidae’, Iberomesornis, Cathayornis, Concornis, Neuquenornis, Eoalulavis, Protopteryx}∼Enantiornithes; {Mononykus, Patagonykus, Alvarezsaurus}∼Alvarezsauroidea.

Two subfossil taxa – Aepyornithiformes and Dinornithiformes – for which character states were only marginally recovered, were excluded for the primary global search, and provisionally placed by means of two different protocols. This measure was taken because simple analysis of these imperfectly known, broadly similar, large ratites led to an apparently artefactual couplet –‘long-branch’ distortions exacerbated by missing data – as sister-group of other ratites exclusive of Apterygidae. First, each was analysed in the absence of the other in a global, unconstrained analysis. Second, each was separately placed by means of heuristic searches in which the primary tree was used as a backbone constraint. The Dinornithiformes were scored as two families (Dinornithidae and Emeidae) as approximated by, ) and ) during character analyses, but analysed as a single, merged taxon in light of their virtually identical scores. Accordingly, the ‘trimmed-merged’ data matrix provided in digital form by ) comprised 150 ingroup taxa and 35 outgroups.

General philosophy

Most standard methodological issues were detailed in the foregoing companion work, including the analytical perspectives that serve to justify the delimitation of characters and states, ordering of states, and related options requisite to preparation of characters for analysis. Noteworthy is a principal reliance on the literature for many characters of non-avian Theropoda. In the present installment, the foregoing characters were subjected to phylogenetic analysis sensu morphological cladistics coupled with the criterion of parsimony of character evolution as implied by the resultant phylogenetic hypothesis. In light of the practical and theoretical implications of adopting the parsimony criterion, alternative methods were not practical for this analysis because of missing data – e.g. optimizations of morphological characters on branching models under selected models of stochastic change or maximum-likelihood analysis. Global parsimony – i.e. minimal total for character-state changes required by final tree (i.e. ‘shortness’) – served as the criterion of optimality for trees recovered through searches. The data matrix was not revised iteratively conditional on outcomes of analysis, nor was ordering of characters conditional on such runs. Instead, the entire data matrix summarized herein was completed prior to the analytical phase, thereby maintaining a partition between (i) definition of characters and states, coding of taxa, and issues of weighting and ordering, and (ii) phylogenetic analysis.

Characters and states

Unfortunate logistic limitations, not oversight or philosophical considerations, prevented the inclusion of character descriptions with the present analytical work. Although a reflection of our unexpected success in defining 2954 morphological characters relevant to the project, it precluded the familiar juxtaposition of descriptive material with analytical inferences. We anticipate that this inconvenience will be ameliorated by the coordinated publication of the descriptive atlas of characters and digitally recorded data matrix, to be made available virtually at cost. We strongly recommend that those interested in the present work procure a copy of its sister publication, as it is through examination of both that meaningful improvements will be made.

Where mutually exclusive states of a single character were diagnosable, a single multistate character was defined. Where two or more included states are observed for a single taxon, a coding of polymorphism was used and analysed specifically as given (i.e. not as uncertainty). The expanse of time reflected by the scale of the analysis also is expected to be associated with the number of multistate characters recognized, i.e. scale of time and taxonomic divergences may be expected to be related directly to scale in evolution of form. Multistate characters encode features manifesting comparatively great evolutionary change and may include greater potential phylogenetic signal, and states thereof will be optimized at multiple internodes. Unless otherwise indicated, characters were analysed as unordered.

Ordering can impose significant constraints on solution sets, and was used only where determined to be defensibly realistic, e.g. naturally ordinated. For example, multistate characters of forms ‘small, medium, large’, ‘absent, miniscule, prominent’, courses of passage of types ‘depressio, sulcus, arcus, tuba’, and junctura of types ‘articulatio, sutura, synostosis’ were considered naturally ordered, counter-evidence lacking. Fundamentally, ordering of states within a character was fundamental to definition and differentiation of characters, basic to the delimitation of states, and represented an extension of parsimony by inclusion of information on linear likelihoods in coding schemes. Such reasoning precluded meaningful use of arbitrary analytical variants such as treating all characters or partitions thereof as unordered. Hypotheses of transformation were sufficiently simple to obviate reliance on step-matrices, linear ordering being the sole condition imposed. Different numbers of states among characters can impose different levels of influence simply by different numbers of state changes among characters, but we considered such differential influence to be realistic and justified as it encoded diverse richness of evolutionary change instead of arbitrarily imposing uniformity on contributions of signal. Therefore, no attempt was made to counter-weight multistate characters. Moreover, no method of explicit weighting – a priori or successive – was employed in this analysis, although some perceive weighting effects to be implicit by other means.

In this work, characters qualifying as autapomorphies at this analytical scale (i.e. apomorphic state limited to single included terminal taxon) were included in all analyses because most served as synapomorphies of the higher-order groups represented by respective exemplars, and many were included in previous publications as diagnostic of the clades represented by exemplars. In addition, such characters are intended to serve others performing lower-level analyses subsequently using some or all of the present matrix. Although autapomorphies did not serve to group taxa at this scale, the limited number detected here were retained because our interests not only included delimitation of clades but also were intended to provide a reasonable representation of evolutionary rates both among internodes and among terminal branches, of interest in many studies of evolutionary rates (e.g., ). Also, autapomorphic differences (deriving from both unique changes or homoplasy) are critical to long-standing issues of perceived (phenetic) distinction and evolutionary divergence among taxa of debated relationships. Furthermore, such characters do not bias support indices such as bootstrapping, and by definition do not influence topologies. Also, a small minority of characters manifesting two or more states in original codings (included in the matrix to permit alternative taxonomic treatments) were rendered invariant by merging and pruning of taxa as detailed herein; this treatment was considered simpler than outright manipulation of the matrix analysed. The primary parameter of logistical concern where parsimony is the criterion of optimization is the number of taxa, a dimension that in the present work was favourably countered by number of characters.

Included characters manifested a range of homoplasy. However, the number of morphological characters employed here exceeded the domain for which meaningful comparison with other works is feasible and evaluation of a suite of related issues – e.g. rates of evolution, notions of relative ‘reliability’ of different data types, patterns of homoplasy, and Markovian informativeness – was not logistically feasible.

Search for optimal solution

The character matrix was constructed using MACCLADE, and analyses were performed on a Macintosh G5 2.5-GHz dual-processor computer. Primary phylogenetic analyses were performed using PAUP* version 4.0b10. Given the size of the data set and the corresponding universe of possible trees delimited, we undertook a thorough exploration of the tree space to circumscribe the optimal solution set, i.e. the set of maximally parsimonious trees (MPTs), summarized graphically by a strict consensus tree of this set.

The set of MPT(s) (min [total length] = 19 553) recovered during heuristic searches in PAUP (MULPARS, TBR, random-addition of taxa, 10 000 random starting trees, MAXTREES = 20 000) was confirmed by a full ratchet-analysis, including five random-addition cycles of 200 ratchet iterations each; the ratchet analyses, employed to escape local suboptima, recovered 97 trees across 1000 topological islands. Choice of optimizations (DELTRAN vs. ACCTRAN) was ineffectual, and neither DOLLO nor IRREVERSIBLE options were used. Of particular relevance to this comparatively large analysis were recent discussions of: (i) efficient means for finding solutions for large data sets, (ii) effects of missing data and (iii) analytical relevance of branch lengths.

Summary statistics used here were: total length, L; consistency index, CI; retention index, RI; rescaled consistency index, RC; and skewness index (g1) based on 105 topologies randomly generated from the same data matrix. Despite its popularity, the CI is negatively correlated with number of both taxa and characters analysed, making meaningful comparisons of indices across scales of analysis and classes of characters is difficult. Characters manifesting homoplasy can impose structural resolution and thereby result in smaller solution sets of MPTs. The set of equally parsimonious topologies (i.e. solutions differing only in optimization of characters on branches of trees of identical topology or solutions differing in branching structure but of equal length) were summarized using a strict consensus tree. Summary statistics for strict consensus trees were component information, Nelson–Platnick term and total information, and Mickevich consensus information.

Support for individual clades was measured by two statistics: (i) percentages of 10 000 bootstrapped replicates in which the node was conserved, indices considered informative even if assumptions concerning precision and absence of bias are unrealistic; and (ii) Bremer (support) indices, the estimated minimal number of additional steps required wherein the given node, by inverse constraint, is not conserved. The latter were estimated using PRAP, metrics similar to the PC-compatible algorithms of ) and ). Ratchet methods were used in order to find the minimum Bremer index by avoidance of entrapment in local optima. For the Bremer (support) indices, 20 ratchet replicates per node were used. The popular alternative protocol, TREEROT, was not employed because its primary asset –‘partitioned’ support indices – were not a priority here and (most importantly) the algorithm lacks the ratchet.

Comparisons with other trees

Tests of alternative hypotheses proposed by other authors were equivalent to local penalties, i.e. minimal differences in total length imposed by the alternative hypothesis, while other aspects of the MPT (exclusive of pruning of taxa essential for comparability) were conserved. These estimates were made by simple transfer of branch(es) within the consensus cladogram using MACCLADE, which holds other topological groupings constant. This procedure differs from searches constrained only to the grouping of interest, typically performed using ancillary searches under inverse constraints, as in protocols for estimation of Bremer (support) indices.

Critical concepts and terminology

‘It is possible[50% likelihood] that – 1) a distant relationship exists between Apteryx and a tinamou-galliform assemblage; … (5) the diurnal birds of prey may be allied to the owls through the Falconidae … It is improbable[formerly widely believed, since discredited] that – 1) a close relationship exists between Rhea and the tinamous; … (3) Pandion deserves familial status in the Falconiformes …’ (: 241), emphasis added.

‘… the mousebirds, or colies, [i] have no close living relatives, … [ii] they are the only survivors of an ancient divergence … Their [iii] closest living relatives are probably …’ (: 363)

Before considering specific findings in the present study, a clarification of critical terms is essential. The first of the foregoing quotes comprises four statements of perceived probability that either make no objective sense or are self-contradictory by conventional standards. Also, the second quote contains three conclusions (i–iii) for a single group based on a single data set that are: either mutually contradictory (i and iii), or of undetermined meaning (ii vs. either i or iii). In cladistic terms, ‘most closely’ implies ‘closely’ in that hierarchy defines relative relationships. Sister-groups are by definition the ‘most closely related’ of any taxa compared. For example, in cladistic terms, an assumption of monophyly of life on earth implies that every taxon has a close relative and/or closest relative, regardless of extinctions. In other words, degree of relatedness is relative: all lineages have a closest relative and therefore a close relative. Sister-groups need not meet some standard of similarity or absolute antiquity of divergence to qualify. However, under an expectation of at least a limited correlation between evolutionary change in morphology with time – neither ‘clock-like’ nor wildly heterogeneous and completely disassociated – sister-taxa can be expected to share degrees of similarity broadly related to time since divergence, such that recency of divergence between sister-taxa tends to be associated with similarity, and antiquity of such divergence to be associated with dissimilarity.

Minimal-length trees or MPTs

The search for MPTs recovered 97 trees of minimal length (19 553 steps) under standard ordering of multistate characters and rooting by outgroup taxa as given (see Methods). This solution set (2.04 × 1011 rearrangements assessed) had the following summary statistics: CI = 0.2432; RC = 0.1664; RI = 0.6842; and skewness, g1|105 = −0.4258.

A strict consensus tree of the MPTs (Figs 10–18) was completely resolved for the Neornithes with the exception of six polytomies (mostly trichotomies, some nested, discussed below), uncertainties sufficiently limited so as to obviate a majority-rule consensus tree for the primary solutions set, or to delimit ambiguity where one or more ‘rogue taxa’ may be influential. The strict consensus tree for the 97 MPTs shared the following summary statistics: (i) component information, 173; (ii) Nelson–Platnick term information, 4367; (iii) Nelson–Platnick total information, 4540; and (iv) Mickevich consensus information, 0.168.

Non-Neornithine Aves

In light of the growing consensus regarding fossil lineages of the Mesozoic and widely employed characters thereof, broad agreement between our findings and those of others treating pre-neornithine birds was not unexpected. Relationships among outgroup taxa in this analysis generally were consistent with recent analyses.

Critical for empirical rooting of ingroup taxa, as opposed to hypothetical ancestors or other synthetic means of proposing polarities, this congruence lends credence to assessments of polarities of characters at the most basal of neornithine nodes (e.g. the divergence of neognathous from palaeognathous taxa). Crocodylians fell as predicted among the basal Archosauria. Principal exceptions from a growing consensus of palaeontologists were reversed positions or irresolution within two pairs (Fig. 12): (i) Troodontoidea (Troodon and Saurornithoides) and Dromaeosauroidea; and (ii) Rahonavis and Apsaravis, the latter couplet being equally parsimonious whether paraphyletic to other taxa or as sister taxa. Details of positions among outgroups are of secondary interest here, but it is noteworthy that the few instances of incongruence with other studies were associated with exceptionally poorly supported nodes or polytomies in the present work (Fig. 12). It is likely that the generally lower support indices among pre-Neornithes reflect missing key taxa and poor preservation of those coded.

Neornithes

‘… it is probable that the majority of living genera [of birds] were in existence by the end of the Tertiary…. Most, perhaps all, of the [modern] orders of birds had become established by the end of the Eocene.’ (: 42)

‘The phylogenetic position of Palaeogene birds thus indicates that diversification of the crown-groups of modern avian “families” did not take place before the Oligocene, irrespective of their relative position within Neornithes (crown-group birds).’: 515)

Strong support for monophyly of the Neornithes (Table 2; Figs 10, 11) was conferred. Notable, however, in the present reconstruction was its poor congruence with the ‘tapestry’ depicted by ), in which only three higher-order taxa – their Ratitae, Galloanserae and Procellarioidea, and monophyly of one contentious order (Caprimulgiformes) – were in significant agreement with corresponding clades in the present analysis. Points of disagreement, however, were abundant and included much of the topological (diagrammatic) structure in the two works, and notably included the following groupings depicted by: fig. 4A): (i) monophyly of {Ratitae, Galloanserae}; (ii) provisional, exceptionally basal placement of Turnix; (iii) very basal positions and interposition of Piciformes, Coraciiformes, Coliiformes, Trogoniformes and Passeriformes; (iv) multiple discrepancies associated with hypotheses of polyphyly of Pelecaniformes and Ciconiiformes, and (v) inclusion of some Gaviiformes, Podicipediformes, Sphenisciformes and Falconiformes among these groups. Topological dichotomies that hierarchically group modern orders of Neornithes were sought (Fig. 10), and these formed the ordinal basis for a higher-order classification (Appendix 1).

In the following, descriptions of findings, statistics of support, etc., were presented in figures, and reference to these was employed in place of repetition of metrics in the text. Consequently, readers are directed to the appropriate figures and tables where narratives refer to robustness, support and relative parsimony of alternative hypotheses.

Modern palaeognathous birds

This analysis revealed the relationships among the palaeognathous birds to be exceptionally resolved, well supported, virtually unambiguous, empirically rich, markedly traditional, and supported by an unprecedented sample of outgroups. The ratites or flightless modern palaeognathous birds have been the subject of more anatomical and molecular study than any other avian group, an important motivation for which concerned diagnoses of plesiomorphic and apomorphic morphological characters in a group widely recognized to represent an early branch among Neornithes but for which useful outgroups were lacking. Basal polarities of characters of plesiomorphic condition among modern and closely related fossil palaeognathous taxa awaited resolution by means of the most primitive Aves, many recovered only recently (Appendix 1).

Taxonomically orientated anatomical studies, emphasizing ratites or more inclusive in scope, ensued during the 19th and 20th centuries, and investigations of phylogenetic emphasis were among the earliest for Neornithes. In some cases, inference of the primary grade of divergences of palaeognathous, galloanserine and other neognathous taxa aided in the recovery of historical patterns and broad outlines of phylogeny of palaeognathous taxa, patterns that were to prove beyond the limits of mtDNA for resolution.

Most prior studies regardless of method – notably excepting early works conceptually confined by the dated biogeographical paradigm of static continents or phenetic perspectives on affinities – have hypothesized that the palaeognathous birds are the sister-group of other Neornithes, the Tinamiformes are the sister-order of the ratites among palaeognathous taxa, and accordingly the ratites are monophyletic. These findings counter early disputes based in part on biogeography, isolated interpretations of fossils, speculations regarding heterochrony and (subsequently admitted) analytical anomalies. Notable in the last of the foregoing categories was the initial inference of a sister-relationship between a neognathous group comprising the Galliformes and Anseriformes and the palaeognathous birds by ), a topology rendering at the outset the polyphyly of neognathous taxa; subsequently these authors depicted the neognathous birds as monophyletic.

Monophyly of the Tinamiformes was supported by the molecular analyses by ) and ), but minimal taxonomic sampling diminished the generality of these inferences. Sister-group relationships of palaeognathous orders – Struthioniformes and Rheiformes, and Dromaiiformes and Casuariiformes – were supported strongly here (Fig. 13) and elsewhere. A minority of earlier findings (Figs 7A, 8B) provided weak evidence of paraphyly of the Struthioniformes and Rheiformes with respect to a sister-grouping of Dromaiiformes and Casuariiformes and also provided weak support for the Apterygiformes as as sister-group to the latter. Despite support indices suggestive of robustness in several of the molecular works, questions regarding Bayesian bootstrap values justify caution in such assessments.

The Apterygiformes, herein placed as sister-group to all other ratites (Fig. 13), have been inferred to occupy a marked diversity of positions in prior studies. Also, the position of the Apterygiformes relative to the extinct Dinornithiformes varied. The Apterygiformes are the most speciose and genetically subdivided of extant orders of ratites, but are significantly less diverse than the formerly sympatric Dinornithiformes.

The position of the Dinornithiformes also remains a point of controversy, in part because of missing data for this extinct, diverse group; monophyly and relationships among members have been confirmed., ) considered the Dinornithiformes to be the sister-group of the Apterygiformes, contrary to, ),, ), ) and the present provisional inferences. In most respects, the topologies for ratites inferred by ) and: fig. 4) most closely approximated that inferred here (Fig. 13).

Missing data for two orders of ratites – Dinornithiformes and Aepyornithiformes – proved analytically problematic if included unconditionally with extant ratites. Unrestricted analysis of these extinct, moderately related, highly divergent, sparsely coded lineages resulted in a suspicious placement of these two orders as sister taxa. The large numbers of missing data in the two extinct lineages, many lacking in both taxa, prompted two alternative analyses to be performed. Global searches of Dinornithiformes (excluding the poorly known Aepyornithiformes) and placements within the MPT as backbone-constraint placed the moas to be the sister-group of other ratites exclusive of Apterygiformes (Fig. 13), contrary to a sister-relationship between these New Zealand endemics as advocated by, ). By backbone-constraints or exclusion of the Dinornithiformes, the Aepyornithiformes were placed as the sister group of the clade comprising Struthionidae and Rheidae (Fig. 13).

Interordinal relationships

The sister-group relationship between the Galliformes and Anseriformes, reaffirmed here (Fig. 13), was inferred previously by, ), ), and substantiated thoroughly using morphological and molecular data. However, marginally supported counter-proposals persist.

Anseriformes

Within the waterfowl (Anseriformes), sequential sister-group relationships of the Anhimidae, Anseranatidae and Anatidae, respectively, was previously demonstrated by ) and confirmed here (Fig. 13). Monophyly of the morphologically diverse and speciose Anatidae, including the true geese (Anserinae) and typical ducks (Anatinae), is essentially beyond dispute. There exist departures from this arrangement by a minority of workers, but this topology has been substantiated using diverse evidence. The historical hypothesis placing the Phoenicopteridae within the Anseriformes (Table 1) was among the early casualties of formal phylogenetics.

Galliformes

The pioneering myological works by ) and ) provided early hints concerning relationships of Galliformes, but unfortunately these surveys were not cladistic and followed ) in considering unique Opisthocomus as an aberrant galliform. Studies of galliform fossils continue to be phenetic in approach. Fortunately, this pattern is likely to change with the increasingly common phylogenetic analyses of galliforms and an improved fossil record.

In the present work, relationships of two families within the Galliformes – Megapodiidae and Cracidae as mutually monophyletic, sequential sister-groups to all remaining galliforms – agree with placements by other investigators. Some workers, however, suggested a sister-group relationship between the two families (superfamily Cracoidea), as opposed to placement as successive sister-groups (paraphyletic) to other galliforms (Fig. 13).

The robust placement of Meleagrididae as sister-group to the Phasianidae sensu lato in the present work (Fig. 13) opposes inclusion of the family among the enormous complement of other galliforms (reviewed by ). The present finding also differs with the indeterminate placement of this distinctive group from most galliforms by ).: fig. 3) depicted the Megapodiidae and Cracidae as basal, successive sister-groups to the diverse and speciose ‘Phasianoidea’; the latter group included Numida and Acryllium (Numidinae) as members of a polytomous assemblage immediately basal to Meleagris, Agriocharus, Tetraonidae, and a clade comprising 39 taxa of other galliforms inviting taxonomic subdivision. Most of the large-bodied genera of phasianoids (e.g. Gallus, Phasianus) and the ‘Old World quail and partridges’ were among a large, basal polytomy of the ‘phasianoids’ exclusive of the guineafowl (Numidinae). Some of the nodes within this large group, including those resolving Meleagridae and Tetraonidae relative to megapodiid and cracid galliforms, were not sustained by: fig. 3) in a strict consensus of 1700 MPTs based on 102 characters. Also, the tree inferred here (Fig. 13) departed from those recovered using molecular data.

The vast majority of galliform taxa are members of a morphologically conservative group, many formerly included among the Perdicidae or Odontophoridae. These taxa also posed problems of resolution in the present work (Fig. 13), and nodes among these taxa were sufficiently weak as to permit alternative local topologies (i.e. a terminal polytomy). ) found that mitochondrial and nuclear DNA similarly resolved groupings within a sparse but broad sample of Galliformes. Basal nodes of the latter taxa are broadly consistent with some higher-order topologies. The single exception among this group (based on included genera) is the strongly supported sister-group relationship between Gallus (Phasianidae) and Numida (Numidinae). The Numidinae were inferred to be the sister-group of the Phasianidae by ) and ).

Marine assemblage

A diversity of mutually distinctive groups of aquatic birds have been the focus of much early speculation regarding the potentially misleading effects of similarities of locomotion leading to morphological convergence. Most evocative of these speculations concerned the Gaviiformes and Podicipediformes (e.g.;, ), foot-propelled diving specialists that prompted arguments based on phenetics, assumptions of ancestral status for fossils, simplistic proposals of evolutionary trends and (most fundamentally) a failure to meet conventional standards of phylogenetic inference. These shortcomings notwithstanding, such proposals from this era gave rise to a general and uncritical acceptance of rampant convergence uniquely afflicting morphological characters, claims that persist to the present day.

Various alliances among the Gaviiformes, Podicipediformes and Procellariiformes were suggested by ), and proved consistent with myological data analysed by, ) and molecular patterns recovered by ). A relationship between the Gaviidae and Charadriiformes was considered plausible by ). Without explanation, however, ) listed the loons and grebes together immediately following the Charadriiformes, in apparent contradiction to his previous opinion. Foreshadowing a natural radiation of marine birds, ) inferred a comparatively close relationship of the Sphenisciformes with other primarily marine orders, and fossil evidence for loons – of only marginal quality, optimistic appraisals by ) and ) notwithstanding – suggests an early origin at least for the Gaviiformes. A phylogenetic alliance among the Sphenisciformes, Procellariiformes, Gaviiformes and Podicipediformes was substantiated as well by ), and this was indicated by ) and ) on molecular grounds.

The comparatively robust skeletal elements of penguins predispose them to fossil preservation, and recently recovered remains hold promise for stratigraphic chronology. The clade of basal marine taxa inferred herein evolved myriad modes of foraging: (i) Gaviiformes and Podicipediformes being extremely specialized foot-propelled diving birds; (ii) Sphenisciformes and Pelecanoididae (Procellariiformes) being wing-propelled diving birds, submarine ‘flight’ of the former rendering members aerially flightless; and (iii) Procellariiformes, comprising hover-foraging Oceanitidae and other families combining wind-powered gliding and plunge-diving. Some fossil groups remain of uncertain ordinal affinity – e.g. the wing-propelled Plotopteridae – and did not merit analysis herein, where states for cranial characters are critical but specimens are woefully incomplete. Early descriptions suggested the inclusion of the Plotopteridae among Pelecaniformes is competitive with an alternative relationship to Sphenisciformes for which pectoral similarities were emphasized. Dissent regarding the ordinal relationships of the Plotopteridae is consistent, to a point, with the interordinal relationships of the Pelecaniformes and Sphenisciformes inferred herein (Fig. 14).

Monophyly of the Sphenisciformes seldom has been doubted, and resolution of relationships among modern and fossil species was achieved, but the position of this distinctive marine group remains a long-standing controversy. This duality of distinct synapomorphy and symplesiomorphy underlies a number of classificatory problems of Aves, in which marked distinction of groups tends to confound comparisons with other groups. Of the alternatives proposed, an affinity with the Procellariiformes has received broadest support, both in the present analysis (Fig. 14) and elsewhere.

Despite agreement with the inferences by ), it is predictable that strong confirmation of a sister-group relationship between the Gaviiformes and Podicipediformes (Fig. 14) herein will engender concerns of artefactual pairing by convergence.: 16) felt that the non-phylogenetic work by ) ‘… demonstrated that the similarities among the loons, grebes, … resulted from convergent evolution …’ The inclusion of the Mesozoic Hesperornithiformes with modern Gaviiformes and Podicipediformes by ), a finding not supported here (Figs 10, 14), was the inference subjected to greatest criticism. Obvious similarities of form and life history have prompted exceptional attention to differences between the two orders (e.g.: table 1), tallies without benefit of polarities or phylogenetics. In many cases, these rationalizations are undermined with respect to functional comparisons, e.g. the Gaviidae employ feet for primary propulsion but also use their wings, and members of the two orders also differ in the movements typical of the pelvic limb. Pairing of the Gaviiformes with the Podicipediformes as sister-groups has been championed by, a proposal not without opposition (e.g.,,;, ). Additional support for this ordinal pairing has been reported, but most other analyses excluded one or both of these key orders, rendering comparisons among such works regarding these orders impossible.

Without a consensus regarding a relationship between the Podicipedidae and Gaviidae, the former have been the subject of several extraordinary proposals, based on relatively weak evidence or mere speculation.: 168), under the subheading ‘Family Incertae Sedis Podicipedidae’, stated: ‘In looking beyond their obvious specializations for diving, I cannot see that the grebes (Podicipedidae) would be out of place in the Gruiformes.’ A more precise proposal for the latter is a possible affinity on myological grounds with the gruiforms Rhynochetos and Eurypyga. An apparent variant of this speculation was a possible relationship with the Heliornithidae and the closely related Rallidae. Also, a tenuous alliance between the Podicipedidae and Cuculidae was depicted by ), but subsequent works have failed to support this grouping. Another position recently inferred for the Podicipediformes relates to the Phoenicopteridae, a proposal considered further below.

In most respects, inferences herein regarding the Procellariiformes were among the least contentious for the marine assemblage, whether in comparison with traditional or modern reconstructions. A moderate departure from traditional arrangements is the finding herein of the Diomedeidae (albatrosses) as comparatively derived, with other Procellariiformes paraphyletic to the typical Procellariidae and Diomedeidae.

Pelecans and allies: totipalmate birds

The totipalmate or pelecaniform birds, as traditionally defined, remain a higher-order group of extraordinary controversy, but in reality the suite of unifying characters, stressed by ), has been expanded for decades beyond the totipalmy cited as sole uniting anatomical character for the order by ). Polyphyly of the order was inferred subsequently by ) and ). The status of the Pelecaniformes has been debated since the core assemblage was included in widely recognized classifications, and points of controversy include those of monophyly, content and interordinal position, as empirically derived from metric, neontological, palaeontological and molecular perspectives.

The exceptional heterogeneity of traditionally included families – e.g. frigatebirds, gannets and pelicans – render questions of membership especially problematic. Perhaps most intriguing of the debated memberships is that of the shoebill or Balaeniceps. Purportedly intermediate features of ‘stork-like’ and ‘pelican-like’ forms have extended to proposals of pelecaniform affinity of the hammerkop (Scopidae). In agreement with the present analysis, the consensus of available phylogenetic works places the distinct Phaethontidae as sister-group to other pelecaniforms exclusive of Balaeniceps, with an alternative position hypothesized for the Phaethontidae as an exceptional plesiomorph allied to some pelecaniforms and the Procellariiformes. The present study also resolved Balaeniceps as sister-group to the clade comprising Phaethontidae and other (traditional) Pelecaniformes. Scopus was not inferred here to be closely related to the Pelecaniformes (Fig. 14), contra).

Relationships among traditional Pelecaniformes (excluding Balaeniceps), inferred cladistically by: figs 6, 7), agreed with the inferences presented herein (Figs 10, 14), whereas comparisons between the studies with respect to the orders Sphenisciformes, Gaviiformes, Podicipediformes and Procellariiformes were not possible. ) proposed a ‘four-fold’ polyphyly of Pelecaniformes among the most notable departures of their analysis from contemporary arrangements, whereas several other traditional elements were conserved in their scheme. ), based on an analysis impoverished in both data and taxa, also suggested polyphyly of taxa traditionally considered pelecaniform in a work remonstrated by ). Syntheses by ) and: fig. 6.3) reaffirmed ordinal monophyly (exclusive of Phaethontidae) using morpho-ethological data, whereas molecular reconstructions violated ordinal monophyly by topologically variable inclusions of the Diomedeidae, Procellariidae and Cathartidae (: fig. 6.2). One minor departure from tradition by ) was a terminal triad in which the Phalacrocoracidae were placed as sister-group to the Anhingidae and Sulidae.

) weakly confirmed monophyly of the traditionally constituted order, in part by use of appropriate outgroups but despite heterogeneous taxonomic sampling of ingroup families. Three weakly resolved departures by ) from the hypothesis inferred herein (Fig. 14) were: (i) reversal of the positions of the Phaethontidae relative to the Fregatidae + Pelecanidae; (ii) a sister-relationship between the Pelecanidae and Phaethontidae; and (iii) paraphyly of Phalacrocoracidae and Anhingidae to the Sulidae.

The Phalacrocoracidae and Anhingidae – families long considered closely related and strikingly similar in external and skeletal aspects – have been subjected to unexpected hypotheses of relationship. A series of related papers, based on limited taxonomic representation of pelecaniform families and unconventional analytical methods, mustered mtDNA sequences and behavioural data that favoured paraphyly of these two families to the Sulidae, also inferred phenetically by ). Based on the present analysis (Table 3), however, a sister-group relationship between Phalacrocoracidae and Anhingidae is strongly favoured.

Storks, herons and allies

‘Wading birds’, as delimited here, comprise the typically long-legged, long-necked storks and herons, and exclude the morphologically reminiscent cranes and allies (Gruiformes) and the potentially allied shorebirds (Charadriiformes). Highest-order nodes resolved in the present study defined a primary division of (i) ‘herons’ from (ii) ‘storks’ and allies as sister-groups (Fig. 14). Among the ‘storks’, Scopus is the sister-group to other members, the latter comprising clades partitioning the (i) ibises and spoonbills, and (ii) flamingos and typical storks. Within the ‘herons’, the only notable finding is the placement of Cochlearius as sister-group to other herons (Fig. 14), an inference consistent with traditional classifications (e.g. ) and earlier findings.

) suggested affinities between the Phoenicopteridae (flamingos) and both the Anseriformes (waterfowl) and the Ciconiiformes (storks and traditional allies). ) questioned the monophyly of the traditional Ciconiiformes on phenetic grounds, suggested charadriiform affinities of Phoenicopteridae and Threskiornithidae, and expressed uncertainty regarding the ordinal placement of the herons (Ardeidae). ), based on conventional molecular estimates and the phenetics of DNA–DNA hybridization, found no support for monophyly of the Ciconiiformes in an analysis including representatives from several other traditional groups. Molecular reconstructions by ), however, confirmed monophyly of the morphologically diverse, ‘true’ storks (Scopus and Balaeniceps not sampled), groupings that also were afforded significant ethological support.

It has been hypothesized in recent years that the Phoenicopteridae may be the sister-group of the grebes (Podicipediformes), a proposal supported by tenuous molecular and morphological evidence (;; but see ). Given the variable viewpoints expressed regarding the Phoenicopteridae as well, this couplet offered the hope of dispensing with two challenging taxonomic placements by means of a single union, a circumstance not uncommonly an artefact of long-branch attraction. Both of these autapomorphic taxa have been subjected to classificatory confusion for more than a century (e.g.;; ), with affinities of the flamingos considered plausible between either the Ciconiiformes or the Anseriformes. Despite robust support for the more traditional position in the present analysis (Tables 2, 3; Figs 10, 14) and the minimal evidence presented by others for the proposal of the Podicipediformes, the latter hypothesis merits examination on the grounds of its superficial implausibility and the marked rearrangements of higher-order avian relationships it would imply. Supplementary morphological support for a sister-group relationship between grebes and flamingos marshalled by ), however, required the exclusion (in a second analysis) of the loons – heretofore the global sister-group of the grebes – to sustain the grouping in question. Both exclusion of the Gaviiformes and narrow sampling of characters and taxa with which the Phoenicopteriformes were evaluated by ) weakened the resultant inferences regarding the relationships of flamingos.

: 148) recovered 50% and 78% bootstrap support for this taxonomic couplet in analyses of different partitions of the ZENK gene, and joined ) in the speculation that: ‘… because both grebes and flamingos are highly derived morphologically and adapted to unique aquatic niches, their potential evolutionary alliance has previously gone unnoticed.’ Unfortunately, this rationalization is vulnerable to criticism because: (i) modifications for foot-propelled diving of grebes are comparable with those of several other groups of Neornithes – e.g. some Anatidae (Oxyurini, Mergini), Gaviidae, Phalacrocoracidae and Anhingidae; and (ii) the ‘unnoticed alliance’ between grebes and flamingos recognized by ) instead was countered by a number of apomorphies in each genus that are shared with other taxa – e.g. Podiceps with Gavia, Phoenicopterus with (other) Ciconiiformes. The present data set supports the rejection of this novel proposal involving the grebes and flamingos (Table 3; Fig. 14), and suggests that the taxonomic proposal for the couplet by ) is premature.

Cranes, rails, shorebirds and allies

The remaining long-legged, statuesque denizens of early successional, often wet habitats, together with the true shorebirds, compose the sister-group of remaining neornithine taxa (Fig. 15). These families, typically included within the traditional Charadriiformes and Gruiformes, have a long, perhaps unequalled history of debate in the ornithological literature (reviewed by,; ). Primary points of controversy concern the monophyly of the Gruiformes, and relationships between the taxa traditionally referred to the Gruiformes and the Charadriiformes; the latter order is known for especially great diversity in structure of the skull.

Gruiformes and allies

In an analysis of phylogeny and flightlessness of the Rallidae, the traditionally delimited Gruiformes appeared to be monophyletic when analysed with only limited outgroups. However, in the more extensive sampling of higher-order groups of the present analysis (Fig. 15), this assemblage was resolved to be paraphyletic to the Charadriiformes. Most families included among the Gruiformes have been the subject of comparatively intense debate with respect to taxonomic position, e.g. ) prepared an addendum for the Rallidae and allied families, and ) revealed the difficulties of resolving the phylogenetic position of the Heliornithidae within the order. Nonetheless, the order contributed to early perceptions of southern-hemispheric origins of many non-passeriform birds.

In the present work, most families formerly included among the Gruiformes were inferred to be monophyletic (Fig. 15), forming a single clade within which a primary bifurcation established the first of two subclades comprising the Otididae and Cariamidae. The second of the primary gruiform clades, and sister-group of the foregoing clade, comprised the sister-groups of (i) Eurypygae (i.e. Eurypygidae, Rhynochetidae and Aptornithidae as sequential sister-groups) and (ii) the nominate suborder Grues (i.e. Psophiidae, Aramidae and Gruidae as sequential sister-groups). New information on the Eocene fossil Eogrus is consistent with monophyly of the Gruidae inferred by other means. With the exception of an alternative position hypothesized for the subfossil Aptornithidae, arrangements of these ordinally defining families have engendered only limited dissent.

Several families formerly included within the Gruiformes by ), as detailed above, were inferred herein to be members of the sister-group of the Gruiformes, and specifically were resolved as two sequential sister-groups of the Charadriiformes (Fig. 15). Several of these have attracted an inordinate interest pertaining to phylogenetic position, diversity of form, intraordinal membership (e.g. Turnicidae) and manifestation of morphological intermediacy of others – e.g. Pedionomidae and Otididae. The present analysis provisionally placed the Turnicidae and Mesitornithidae as sister-taxa and the first of the two sequential sister-taxa (taxa paraphyletic) to the Charadriiformes (Fig. 15). ) agreed with both the present analysis and that by ) regarding an affinity between the Turnicidae and Gruiformes, but ) proposed a close relationship between the Mesitornithidae and Cuculiformes. The remaining sequential sister-group (lineage in this grade) comprised the Rallidae and its sister-group Heliornithidae (Fig. 15), a close relationship inferred both by ) and ), among others.

Charadriiformes

The preceeding clades subtended a clade herein interpreted as comprising the Charadriiformes. The true shorebirds, as resolved here (Fig. 15), comprise families of comparatively obvious ordinal affinity and great apomorphy, and generally accepted as monophyletic. Relationships among several major groups of charadriiform birds have been inferred (e.g. ); however, the systematics of the group remains markedly controversial.

The present analysis established the monophyly of the Charadriiformes, of which the Pedionomidae constituted the sister-group to other members (Fig. 15). The latter finding represents a slight departure from the marginal inclusion of Pedionomus among Gruiformes and affinities of the genus with the charadriiform Jacanidae and Rostratulidae inferred by ), and is consistent with the inferences by ) and ). Within the Charadriiformes, Pedionomus is the sister-group to: (i) the bifamilial couplet comprising the Jacanidae and Rostratulidae, (ii) the monotypic Dromadidae and (iii) a clade comprising Thinocoridae and the sister-families Scolopacidae (e.g. Heteroscelus) and Phalaropodidae (Fig. 15); and (iv) a terminal clade comprising two major subclades and multiple, only partially dichotomously resolved families (Fig. 15). These broad groupings bear notable similarities with the suborders defined by ).

The remaining clade of the Charadriiformes comprises two major subclades, both of which are weakened by three marginally robust, defining nodes (Fig. 15). The first comprises in turn three lineages or subclades: (i) the Charadriidae; (ii) the sister-groups Cursorinae and Glareolinae (collectively constituting the Galreolidae); and (iii) a clade comprising the Burhinidae and its sister-group comprising two bifurcate clades, the Haematopodidae (united exclusively with monotypic Ibidorhynchus), and the Recurvirostridae (united exclusively with monotypic Cladorhynchus). The other major, pectinate subclade within the Charadiformes comprises, respectively, the sequential sister-groups Chionididae, Alcidae, Stercorariidae, Rynchopidae and Laridae (Fig. 15).

Birds of prey–diurnal and nocturnal

Raptors or birds of prey – comprising the diurnal Falconiformes and (principally) nocturnal Strigiformes – share a primary reliance on carnivory, by scavenging or capture of prey and associated functional commonalities. The sister-relationship of these raptorial orders inferred herein (Figs 10, 16) and by ) has been the subject of suspicion based on phenetic tallies of differences and speculations concerning convergences and raptorial specializations. However, these orders differ in many respects and manifest substantial diversity within orders, conditions as suggestive of comparatively ancient divergence of sister-groups sharing general raptorial lifestyles and independent (order- and family-specific) morphological refinements. This clade is first in a sequence of four – the birds of prey, Opisthocomus, Cuculiformes, Psittaciformes and Columbiformes – that are sequential sister-groups of remaining Neornithes. Although all of these orders were robust with respect to individual monophyly, the four highest-order branches supporting these orders were not (Figs 10, 15–17), rendering the branching sequence provisional.

In addition to suspicions of convergence, several concerns may be seen as opposing the phylogeny inferred herein: (i) an alternative interordinal hypothesis that presumes the Strigiformes to be most closely related to the non-raptorial but similarly nocturnal Caprimulgiformes; (ii) an hypothesis that holds the New World vultures (Cathartidae) to be more closely related to the Ciconiidae than to typical birds of prey; and (iii) several counterproposals concerning certain families and genera of Falconiformes, notably positions of the terrestrially specialized secretary-bird (Sagittarius serpentarius), the piscivorous ospreys (Pandion haliaetus), and the distinctive Falconidae relative to other diurnal raptors.

Falconiformes

In the present analysis, however, Cathartidae was resolved as the sister-group of other Falconiformes – an inference considered ‘probable’ by ) – and the Sagittariidae was sister-group of the order exclusive of the Cathartidae. The Falconiformes, exclusive of the foregoing two families, comprised a pair of sister-clades: (i) the Accipitridae, including Old World vultures (e.g. Gyps), and (ii) a clade comprising the Pandionidae and its sister-group the Falconidae, the latter including the caracaras (Fig. 16).

,,, ) comparatively surveyed morphological characters of the Falconiformes in a monograph largely limited to anatomical phenetics and influenced by suspicions of functional convergence. Exclusive of primarily syringeal evidence, the only phylogenetic study of diurnal raptors based on morphological characters remains that by ). Unfortunately, most studies treat most families within the Falconiformes (as construed herein) in only limited capacitiy or secondary focus, e.g. as outgroups for the Falconidae, or in treatments of other phylogenetic issues within the Accipitridae. Cytotaxonomy appears to possess signal, especially in the comparatively intensively studied Falconiformes, but even phenetic groupings of cytotaxonomy have defied interpretation. The recent sequence-based phylogeny proposed for the diurnal birds of prey emphasized species-level relationships within the Accipitridae, and ) failed to resolve relationships among the diurnal raptors. ) differed from the present analysis in the placement of Pandion as more closely related to the Accipitridae than to the Falconidae or Phalcobaeninae. A sister-group relationship between Cathartidae and other Falconiformes, as inferred herein (Fig. 16), was recovered by ), although the latter differed regarding the Strigiformes, Accipitridae and Falconidae.

) tallied characters suggestive of a phenetic ‘affinity’ between the Cathartidae and Ciconiiformes. Evidently derived from studies by ), ) and,,,, ), works that included Pelecaniformes and Procellariiformes as alternative candidates, the work by ) was a comparison of favoured features solely between the Cathartidae and selected representatives of Ardeidae, Ciconiidae and Accipitridae. ) did not consider polarities or include a formal analysis based on a broad array of characters, and most of the phenetic differences are not convincingly distinct; many features were cast in terms of antiquated typology, such as the ‘palatal types’ of ). Nevertheless, this hypothesis found a receptive audience, and it arguably is more popular than it is empirically robust.

) concluded that limited mtDNA sequence data supported a close relationship between the Cathartidae and storks. Subsequent analyses of the data used by ) – revised and augmented by ) and ) – largely were not comparable because of methodological differences. ) and ) compiled weak molecular evidence to test the hypothesis, the results of which were equivocally consistent with the hypothesis of ). Analyses including these taxa during the following decade (Figs 1–10) failed to support the exclusion of the Cathartidae from Falconiformes sensu stricto, or associate the family with the Ciconiiformes.

Strigiformes

The other substantive debate regarding birds of prey concerns the relative support for a sister-group relationship between: (i) diurnal and nocturnal raptors, or (ii) the similarly noctural Strigiformes and Caprimulgiformes. The current analysis strongly confirmed a sister-group relationship between the Strigiformes and the Falconiformes (Fig. 16), a union also supported by ), ) and ). Recent molecular studies have placed the Strigiformes tenuously with a striking diversity of taxa, including the Psittacidae, Picidae and Rhamphastidae. Fossils that exhibit generalized raptorial characters or those of both Strigiformes and Falconiformes also have been described.

With respect to familial relationships within the Strigiformes, the present analysis reaffirmed a basal bifurcation between barn-owls (Tytonidae) and typical owls (Strigidae), with the former including Phodilus (Fig. 16). Phodilus (bay owl) has been considered of variable intermediacy to both strigiform families (Table 1), but most recent molecular data bearing on Phodilus (G. Barrowclough, pers. comm.) are consistent with the present findings (Fig. 16).

Hoatzin, cuckoos, pigeons, parrots and allies

This group of medium-sized landbirds approximates part of the ‘Anomalogonatae’ of ) and ), largely synonymous with the earlier branches within the ‘higher landbird assemblage’ of ). Clades informally included in this grade of modern landbirds are characterized by mutually exclusive apomorphies rendering many of the groups among the most readily recognized of birds. Members of this subterminal grade of avian orders have been the subject of numerous studies, but nonetheless a clear consensus regarding their interordinal affinities has failed to emerge. As noted previously, these taxa –Opisthocomus, Cuculiformes, Psittaciformes and Columbiformes – traditionally were accorded ordinal rank, and were resolved here as a grade in which defining nodes achieved only marginal support. Accordingly, this series of clades conservatively can be considered to compose a tri-ordinal grade or corresponding polytomy that bridges the Cuculiformes with the Caprimulgiformes and Apodiformes. The latter ambiguity primarily relates to the failure to resolve the order of branching of the Psittaciformes relative to the Columbiformes (Fig. 17). Nevertheless, the orders branching from this grade were each strongly supported.

The Opisthocomidae – solely comprising the unusual hoatzin (Opisthocomus hoazin) – has been allied with Tinamidae, Galliformes, Cuculiformes, Columbidae, Pteroclidae, Rallidae, Otididae and Coliidae, among other higher-order groups (Table 1). Recent attempts to resolve the uncertainty of position of this monotypic lineage by molecular means have proven largely unsuccessful, principally by mutual contradiction or ambiquity of findings, and also because of contaminated sequence data. A growing number of works are at least consistent with an affinity between Opisthocomus and the Cuculidae, despite disputes regarding method and differences in taxonomic sampling. In the present analysis, Opisthocomus was placed as the sister-group of the Cuculiformes, the latter weakly including the Musophagidae as sister-group to the Cuculidae (Table 2; Fig. 16).

Uncertainties of phylogenetic position and superficial plesiomorphy of Opisthocomus led some (e.g.,; ) to suggest that the taxon derives from the ‘roots’ of Neornithes. This proposal is consistent with a perception that the species descended from uniquely primitive ancestry, a view exemplified by its description as a ‘reptilian’ bird by ), its use as the only neornithine explicitly figured with Archaeopteryx or non-avian Theropoda (;: fig. 26), and the much-publicised retention and use of weakly functional ungues alulares in the genus prior to fledging. In actuality, such ‘wing claws’ are retained by members of many modern avian orders in variably vestigial states. Accordingly, morphological and molecular evidence for the purported plesiomorphy of Opisthocomus is ambiguous at best: most studies place the genus as closely related to the Cuculiformes (; present study), whereas a few analyses suggest a more distant relationship.

Various other studies, most with only marginal taxonomic sampling, have inferred a sister-group relationship between Opisthocomus and the Cariamidae or inclusion within an eclectic assemblage defying plausible explanation in light of other findings. The unique alimentary features of Opisthocomus, notably refinements for herbivorous or ruminant digestion, are of little phylogenetic significance as they are autapomorphic among Neornithes. However, the lysozymes associated with fermentation by, ) suggest Opisthocomus to be more similar to Columba than Gallus.

Phylogenetic studies of the Cuculidae per se are surprisingly few, but include taxonomically inclusive attempts at morphological and ethological insights as well as a molecular exploration. ) compiled characters distinguishing the Cuclidae from the Musophagidae, many of which show homoplasy at wider scales of comparison. The molecular study by ), the primary focus of which were the Malagasy couas, resulted in a topology within the family broadly similar to that inferred herein, differences in sampling notwithstanding (Fig. 16).

Pigeons and sandgrouse

The Columbidae traditionally are recognized as monophyletic, whereas the interordinal position of the Columbiformes remains a primary point of dispute. The incompletely resolved position inferred here (Fig. 17): (i) compares reasonably well with the semi-speculative tree by ); (ii) accords acceptably with the poorly resolved reconstructions by ), ) and ); and (iii) is only weakly congruent with the placements by ) and ). The fossil record of the Columbidae from the Palaeogene is poor, and described as non-existent by ). Sampling of the Columbidae was comparatively intense in the present study so as to affirm the monophyly of such a diverse family and to expand the thoroughness of placements of the extinct ‘raphids’Raphus and Pezophaps.

The present analysis indicated monophyly of flightless Raphus cucullatus and Pezophaps solitaria, one of the principal hypotheses proposed for the ‘raphids’. Goura and Didunculus, historically speculated to be sister-genera, were placed as paraphyletic to the raphids (Fig. 17). These inferences general agree with those by: fig. 1) and, ), and revealed generic partitions within the Columbidae in considerable agreement with the present work. The Pteroclidae (sand-grouse) have been the topic of study for more than a century. The pteroclids were placed herein as the sister-group of the Columbidae – a view favoured by the majority over an hypothesized alliance with the Charadriiformes.

Parrots and allies

The primary mystery of this unique order is its interordinal position, a debate clearly manifested by the myriad groupings inferred for it in phylogenetic works during the last two decades. Monophyly of the Psittaciformes, not amenable to testing with the few exemplars included here, has been assumed or affirmed by diverse morphological and molecular means. Higher-order relationships are less clear, and the order has been allied with: (i) groups comprising sufficient diversities of neognathous taxa as to establish little progress; (ii) Trogonidae and/or Coliidae; (iii) Picidae; (iv) Coliidae and some Pici; and (v) Strigidae. Although the present analysis provides no single, well-supported and precise position for the order, the evidence compiled herein is consonant with a (perhaps deep) relationship between the Columbiformes and Psittaciformes. This interordinal union was inferred by ) in a study of Didunculus, and also confirmed by: 241) and ).

Overview

This heterogeneous group of moderate to small landbirds of controversial relationships – approximately synonymous with the ‘Coccygomorphae’, the Anomalogonatae, or part of the ‘ “higher” landbird assemblage’ – includes some of the most specialized and distinctive of modern birds. Unlike the foregoing groups, most higher-order nodes within this assemblage – i.e. those structuring relationships among orders – are robustly resolved (Fig. 17). Essential findings herein were monophyly of the traditional Caprimulgiformes (including Aegothelidae), and monophyly of its sister-group Apodiformes. The Apodiformes comprised the crested-swifts (Hemiprocnidae) as sister-group to a clade comprising the mutually monophyletic typical swifts (Apodidae) and hummingbirds (Trochilidae).

Caprimulgiformes

A minority of works failed to recover monophyly of the Caprimulgiformes, either by unresolved polytomy, variably constituted paraphyly to Trogonidae or Apodiformes, or uniquely proposed alternative alliances with the Accipitridae and Sulidae, Sagittariidae, or Mesitornithidae. The present phylogeny affirms monophyly of the traditional Caprimulgiformes, although recent analyses suggest that the present study may not have been adequate to capture all ‘family-level’ variation in the order by omission of Batrachostomus and Eurostopodus. The moderately distant relationship between the nocturnal Caprimulgiformes and Strigiformes – considered closely related by some – was favoured herein, a finding consistent with the hypothesis that at least the ocular refinements for nocturnality in these two orders are not homologous. In this context it is noteworthy that another aspect of colour vision shows low consistency with avian phylogeny. Support for groups within the Caprimulgiformes in the present work was marginal at best, and for practical purposes might be considered to be a polytomy of the included families. Palaeontological proposals suggest that fossil members of the Caprimulgiformes (and certain other groups) currently endemic to the southern hemisphere previously extended to the Palearctic.

) also presented equivocal evidence that the owlet-frogmouths (Aegothelidae) are not members of the Caprimulgiformes, as traditionally classified, a proposal augmented by some morphological evidence and DNA sequences. The latter studies led to marginally supported transfers of the Aegothelidae – herein inferred to be the sister-family of other Caprimulgiformes – to an alternative position as sister-group of the Apodiformes, a reasonably economical concession from global parsimony using the present data set (Table 3). Although the position of the Aegothelidae remains uncertain, mtDNA sequence data are consistent with the monophyly of this family. A complete picture of caprimulgiform phylogeny must await comprehensive integration of putative fossil members.

The oilbird (Steatornis caripensis) – a nocturnal, cavernicolous frugivore – is one of the most challenging of avian genera with respect to phylogenetic position, irrespective of method. Recent analyses have differed regarding even the ordinal placement of this taxon, traditionally assigned to a monotypic family. The present work tentatively resolved Steatornis to be a highly apomorphic member of the Caprimulgiformes (Fig. 17).

Apodiformes

This order is monophyletic and, as traditionally construed, comprises the highly derived crested-swifts, swifts, swiftlets and hummingbirds. The interfamilial relationships inferred here (Fig. 17) – Hemiprocnidae (crested-swifts) as sister-group to a clade comprising the mutually monophyletic Apodidae (swifts) and Trochilidae (hummingbirds) – have received growing support from other works (e.g. ) in tabling the largely antiquated contention that the hummingbirds were closely related to the Passeriformes and related variants of this hypothesis (Table 1). Departures from the present hypothesis included that of monophyly of the Hemiprocnidae and Apodidae. The molecular phenetics of ), including where re-analysed or augmented, also differed by resolving the Trochilidae as phenetic ‘sister-group’ to all other Apodiformes, prompting the former to be ordinally distinguished as Trochiliformes. The speciose hummingbirds (Trochilidae) achieved phylogenetic diversity in concert with the related apodids, a radiation second only to passeriforms in scale, and evolved a diversity of concomitant apomorphies, some of which overcame unique locomotory challenges (e.g. ). Phylogenetic study of the swifts (Apodidae) by palaeontological and molecular means, resolved a fundamental dichotomy between taxa possessing capacities for echolocation.

Coliiformes and Trogoniformes

Modest support was afforded herein to a sister-group relationship between the Trogoniformes and Coliiformes (Fig. 17). Both orders have proven challenging to place among other avian orders, but monophyly of these orders has not be questioned. The present analysis confirms earlier anatomical and molecular analyses, in which this couplet also was inferred in turn to be closely related to Coraciiformes. ) conceded that appropriate outgroups for rooting analyses of these orders was problematic, a problem that led ) to employ a suite of outgroups. Among the more notable expansions of palaeodistributional limits have pertained to the Trogoniformes and Coliiformes, although diagnostic evidence was poor by general neontological standards.

This couplet raises the possibility of artefactual grouping by way of long-branch attraction. Examination of ranges of terminal branch lengths compiled in the MPTs –Colius (84–133) and Trogonidae (10–17), with the branch subtending clade having a range of lengths 36–97 – suggests that the Trogonidae are not obviously vulnerable to an artefactual grouping. This judgement is supported further by the inclusion of a number of multistate, supportive characters.

Overview

Long recognized as a speciose, diverse and widespread group, historical disagreements pertaining to these orders have turned on familial memberships (e.g. Trogonidae) and delimitation of orders within the assemblage (;;: 241). Predictably, some subgroups manifested intermediate suites of characters and have proven least tractable (: fig. 32); the latter have been addressed most pointedly, perhaps, in palaeontological diagnoses. Also, where data are less numerous, a common alternative to monophyly of the Coraciiformes or Piciformes is resolution of the two as sequential sister-groups (paraphyletic) to the Passeriformes. Although monophyly of the tri-ordinal assemblage was substantiated here (Figs 17, 18), the analysis revealed several alternative arrangements among the three orders, represented by the polytomy in the strict consensus tree of MPTs (Figs 17, 18).

Coraciiformes

Monophyly of the families traditionally included within the Coraciiformes has been a point of disagreement for almost a century, and persists as a palaeontological challenge. This state of affairs has been prolonged by poor representation of the order in many recent family-level, multi-ordinal analyses (e.g.; ), with notable exceptions including the analyses by ) and ). Taxonomically narrow analyses include morphological works by ), ) and ), and the molecular phenetics of ) and ).

The Coraciiformes were found herein to be a monophyletic member of a trichotomy that included the Piciformes and Passeriformes (Figs 10, 11, 17, 18), but the magnitude of support for monophyly of the Coraciiformes was only moderate, and generally was exceeded by that for included nodes. The ordinal work by ) proved most relevant in this context, but conclusions of the two analyses differed considerably. Evidently, restriction of the outgroups and characters included in the analysis by ) resulted in contradictory findings symptomatic of diminished signal, e.g. inversions of taxa within the ingroup and inclusion of Trogonidae within the ingroup.

The very distinctive hornbills (Bucerotidae), together with a sister-group comprising the Upupidae and Phoeniculidae, were situated as the sister-group of other coraciiforms (Fig. 18). This group was considered a separate order allied to other Coraciiformes by ) and ). ), however, inferred the Coraciiformes to be polyphyletic and comprising: (i) the ‘Bucerotes’ (Upupidae, Phoeniculidae and Bucerotidae) as sister-group to the mutually monophyletic Piciformes (including Galbulae) and Passeriformes; (ii) the ‘Alcediniformes’ (all other members of the traditional order not included elsewhere); and (iii) Leptosomus, excluded from the Coraciiformes and of indeterminate ordinal relationship.

The remaining members fell into two sister-groups: one of these comprised the Motmotidae and its sister-group comprising the Todidae and Alcedinidae, the Todidae of uncontested monophyly, and the Alcedinidae monophyletic but perhaps comprising two or more distinct subgroups. The remaining member of this pair of sister-groups comprised the sequential sister-groups of Meropidae, Coraciidae, Brachypteraciidae and Leptosomatidae (Fig. 17). The Motmotidae were inferred herein to be the sister-group of a clade comprising the Todidae and Alcedinidae. However, some ‘intermediacy’ of morphological and molecular characters of the tody-motmot (Hylomanes) and the Todidae suggests possible paraphyly of the Motmotidae (as traditionally constituted) or the Todidae. The Meropidae (bee-eaters), of established monophyly, were inferred here to be the sister-group to remaining Coraciiformes (Fig. 17), the latter known in the vernacular as ‘rollers’. As detailed above, morphological assessments of the memberships and positions of these families differ significantly.

Piciformes

The Galbulidae and Bucconidae were inferred herein to be sister-groups, and together as forming the sister-group of other Piciformes. The remaining Piciformes in this analysis comprised two sister-groups (Fig. 18), each of which comprised two, provisionally monophyletic families: (i) Capitonidae and Rhamphastidae; and (ii) Indicatoridae and Picidae. Support for neither of the latter clades was strong, approximating only 50% bootstrap support (Fig. 18). This arrangement is consistent with much of the classification proposed by ). One point of current debate is the possible paraphyly of the Capitonidae, in which member taxa represent successive sister-groups to the (monophyletic) Ramphastidae (e.g.;;; ). Unfortunately, despite comparative richness of the record, fossil members of these groups have provided few insights into the phylogeny of modern piciforms.

Monophyly of the Piciformes, most often challenged regarding membership of the Galbulae, has been controversial – e.g. ), ), ), ) – despite comparatively detailed anatomical study and related phylogenetic analyses. Most attempts to reconstruct the phylogenetics of the order have been variably inclusive with respect to included families and limited to molecular evidence, and resultant findings posed no serious contradictions to the inferences made here.

Passeriformes

The Passeriformes are a dominant evolutionary component of the global avifauna, and the phylogeny of the order has figured prominently in terminological disputes regarding faunal ‘radiations’, ‘key innovations’ of evolutionary change and ‘evolutionary success’. Current consensus by avian systematists holds the Passeriformes to be one of the most recently differentiated and apomorphic of lineages of modern birds, with a growing body of evidence for Gondwanan genesis. However, analyses limited to the mitochondrial genome, the early mainstay of sequence analyses, resulted in several studies in the placement of Passeriformes as the sister-group of most or all other Neoaves, a topological shift of exceptional magnitude and enormous evolutionary implications. This finding, mirrored by the phenetics depicted by ) and very recent analyses based principally on mitogenomics, since has been attributed in subsequent works to (unavoidable) reliance on most closely related but nevertheless distant outgroups – e.g. Crocodylia, Testudines – which probably serve as unreliable sources of information on avian polarities. This circumstance, compounded by weak taxonomic sampling or shortcomings of mitochondrial data for reconstruction of deep nodes (e.g.; ), necessitate caution in corresponding inferences. Fortunately, with respect to genomes analysed, principal differences reduce to rotations of three or four variably nested nodes (: fig. 3).

As for monophyly and composition of the Passeriformes, the present analysis was necessarily limited to selected genera and families of this enormous group, as were the few previous morphologically based phylogenies of the group. A number of passeriform subgroups, mostly at comparatively low taxonomic levels, appear to have undergone cladogenesis sufficiently recently to reflect vicariance related to recent glaciations and current continental patterns, but controversy regarding this tempo persists. The meagre palaeontological evidence available indicates an origin of the Passeriformes to be no later than the early Eocene.

The present analysis substantiated the interordinal position and monophyly of representatives of major subgroups of the Passeriformes (Fig. 18). Within the narrow taxonomic sample analysed herein (cf.;;;;; ), Menura was resolved as the sister-group of other members of the order, i.e. a member of the non-passerines (Fig. 18). Menura typically is situated crownward of basal Acanthisitta (but see; ) and included among the basal oscine passerines (;; but see,,, ). This minimally exemplified and questionably resolved subgroup was inferred to be the sister-group of remaining passeriforms, first followed by a poorly represented grade of suboscine passerines (Tyrannides) – Tyrannidae and Pittidae. The Tyrannides in turn subtends the oscine passerines (Passerides), within which two major subgroups were sparsely represented but arranged in accord with current consensus (Fig. 18). ) inferred the Ptilonorhynchidae to be the sister-group of the remaining passeriform taxa. Among other Passerides, the single exemplar of the Corvida (Aphelocoma) was the sister-group of the three representatives of the Passerida –Bombycilla, Parus and Passer. With the exception of the position of Menura in the present analysis, the broad subdivisions inferred here agree with the majority of other recent works and are consistent with palaeogeographical evidence for an Australasian origin for the oscines.

Branch lengths and evolutionary change

Morphological characters employed in cladistic analyses tend to be held to unrealistic standards, and to serve as sources of insights (not expected of molecular characters) beyond mere inference of phylogenetic relationships. For example, in some circles there is an expectation that, in addition to resolving phylogenetic relationships of multiple taxa, apomorphies supportive of nodes should make obvious functional sense (e.g. debates regarding aquatic lineages and possible convergences) and permit interpretation resembling lists of (semi)diagnostic characters for nested series of taxa. In some cases, particularly where taxonomic scale is low and a functional focus pertains, such patterns and trends are discernible. However, with increasing taxonomic scale, these are in the minority, and like DNA sequence data, such diagnostic transparency and functional interpretation is seldom attainable. Many subtle features possessed of phylogenetic signal may be structural artefacts of functionally neutral details of anatomy, historical accidents that prove variably reliable through the process of evolutionary modification with descent.

Nevertheless, quantification of evolutionary change is critical to estimates of rates and correlation of change among characters and related evolutionary topics (e.g.,; ), and exploration of this aspect of reconstructions is intended to pre-empt misplaced expectations or distorted perspectives. The tempo and mode of morphological evolution and cladogenesis have held the interests of systematists for decades, pre-dating the advent of molecular methods or assumptions made for them (e.g. uniform or ‘clock-like’ evolutionary rates). Antiquity of lineages provides opportunity, other parameters being equal, for increased expectation of evolutionary changes (probabilistic, not deterministic expectation), and where such lineages comprise only modest numbers of members – i.e. limited evolutionary opportunities for departures from uniformity or reversals within a given lineage – such change also tends to lead to comparatively direct diagnosticity of terminal lineages. Intuitive relevance of origins, ages, longevities of lineages and expectations of evolutionary divergence notwithstanding, these topics have been underserved by newly acquired empirical evidence.: table 2) listed 14 avian families construed to show molecular variation significantly lower than that expected on the basis of current taxonomic status. Given present findings, however, this issue appears illusory, with virtually all taxa in question having early origins, including the Anhimidae (Anseriformes), Podicipedidae and Spheniscidae, three being members of the Pelecaniformes, and the remaining examples members of either the Ciconiiformes, the Gruiformes or the Charadriiformes.

Unlike molecular evolution, no strict assumptions or dependence on constant or uniform rates of change have been made for morphological characters. In the present analysis, branch lengths varied substantially depending on specific optimizations, and therefore comparisons of lengths, like the internodes in trees, were not restricted to unambiguous changes. Instead, central tendencies of branch lengths of MPTs were quantified by median lengths, and variation among optimizations by standard deviations and ranges of lengths recovered. For Neornithes, numbers of changes optimized as autapomorphies averaged 41 (SD = 33, range 4–186). By contrast, for single lineages, maximal lengths of terminal branches were: 186 for Spheniscus, 132 for Phoenicopterus and 131 for Mesitornis. Minimal lengths of terminal branches were: 4 for Francolinus and Alectoris. At higher phylogenetic scales (interordinal and interfamimlial), branch lengths had the following summary statistics: mean = 36, SD = 33, range 5–133. In general, then, terminal branch lengths were approximately 10% greater than those of the branches subtending them (i.e. deeper internodes). A pattern of short internodes has been inferred previously, but the attribution of cause to realities of evolutionary intervals vs. diminished power of resolution remains contentious.

A survey of the minimal branch lengths included in the MPT revealed that branches among higher-order nodes were extraordinarily similar to associated terminal branches (latter being those subtending individual taxa) in means and variances of branch lengths. However, comparative numbers of the more critical diagnostic and supportive characters within the Neornithes revealed that character-based definitions of highest-order clades (corresponding to the most ancient of synapomorphies) were disappointingly low, whereas those for superorders and orders (Appendix 2) were comparatively robust and included suites of diagnostic character-states (Table 2). However, the correspondence among ‘raw’ branch lengths, statistics of nodal support and numbers of ‘diagnostic’ apomorphies generally was poor (Table 2), in agreement with the findings of ) and ).

Broad comparisons with prior studies

‘Survival of the fittest will decide which of the many competing theories [of avian phylogeny] will prevail. Only one can survive. Each revisor attempts to shorten the struggle by acting as a selective factor.’ (: 269)

‘Where the root of the Neoaves goes, however, is highly uncertain and seems likely to remain a very difficult problem.’ (: 39)

Perspectives and findings

In the published record of phylogenetics, it has become virtually customary simply to generate phylogenetic hypotheses of varying consonance with little or no consideration of factors underlying divergent inferences (Figs 1–9). This tradition has led to a false sense of congruence among studies, especially among molecular systematists. We consider that it is incumbent upon authors to consider the points of disagreement as well as the most plausible underlying philosophical and empirical reasons for the differences. A reasonable degree of detail in such deliberations inevitably will include points of contention and opinion, and we hope that these will challenge the current ambience of consensus and invite constructive debate of these important issues. At the same time, however, it is logistically unfeasible that large-scale studies (e.g. the present work) be held to standards of character descriptions and illustrations in analytical works that are logistically realistic in more common, small-scale works. For example, in the present study, a conservative estimate of character-states eligible for illustration would approach 7000. Nonetheless, access to underlying data for all studies should be made practically available by alternative means, and include formal descriptions of characters as analysed, and essential figures and references to critical descriptive works (e.g. ).

Deep tradition and the ‘tapestry’

Broad affinities of long standing between avian orders – traditionally only implied to variable degrees by adjacency in linear classifications – that were not supported by the present analysis were: (i) Galliformes as closely allied with Falconiformes; (ii) Gaviiformes, Podicipediformes and Sphenisciformes placed as the most basal of ‘Carinatae’; and (iii) a truly basal position of Opisthocomus among Neornithes. Although confidence in the ‘tapestry’ (e.g. ) diminished markedly within a few years of publication, the proposals by ) were ‘rewoven’ by ), ‘dusted off’ by ), and continue to be cited for justification and design of sequence-based analyses (e.g. ). Limited reverence for the tome by ) lingers, most conspicuously in the non-systematic literature (e.g. ), principally because of its taxonomic scale and molecular basis (e.g.; ).

Given the controversy and contradictory nature of the era, it is appropriate to compare our findings with the groups delimited by ), bearing in mind that the present phylogenetic analysis is of limited comparability with the phenetics of DNA–DNA hybridization. First, despite the unprecedented number of taxa analysed, the earlier work was invalidated shortly after its appearance because of problems stemming from phenetic methodology, sparsity of the distance matrix, absence of a root and irreducibility of data-type, some deficiencies having been identified prior to its release. Simplification of the reconstruction by: figs 354–356) to ordinal terminal taxa (Fig. 4) reveals the diagram to be continuously pectinate throughout most of the neognathous birds, and largely reflects ‘chaining’ of least dissimilar elements, an artefact common to some agglomerative algorithms. ) considered current knowledge of avian phylogeny to be of comparable irresolution.

A most peculiar aspect of the ‘tapestry’ is the reversal of mid-basal and apical higher-taxa – e.g. Piciformes and Passeriformes as sister-groups to the ‘Ciconiiformes’ (sensu) and allies – a finding countered by the vast majority of other analyses. This phenetic artefact undoubtedly contributed to the poor congruence of the present phylogenetic hypothesis with that by ), in which only four higher-order groups – their Ratitae, Galloanserae and Procellarioidea, and monophyly of one currently contentious order (Caprimulgiformes) – showed broad agreement in both works. The present analysis strongly countered the polyphyly inferred by ) for the Pelecaniformes and Columbiformes, and differed as well regarding paraphyly of the Coraciiformes and Cuculiformes, the alternative positions of Galliformes + Anseriformes, and the provisional placement of the Turniciformes (Fig. 4).

: 240–241) listed 34 summary inferences entitled ‘Probabilities and Possibilities’, presented under four levels of perceived likelihood. Of the conclusions listed, agreement (with minor qualifications) with the present analysis was achieved for: all eight (100%) of the ‘highly probable’ conclusions; seven of ten (70%) deemed ‘probable’; four of ten (40%) considered ‘possible’; and only two of six statements (33%) classified as ‘improbable’, essentially logical negations of views included among the ‘highly probable’.

Contemporary studies

Comparisons among most phylogenetic hypotheses are compromised by differential taxonomic sampling and nodes afforded only tenuous support. The present phylogenetic hypothesis, depicted to ordinal scale (Figs 10, 11), approximated the tree depicted by ) most closely of prior works, issues of comparability notwithstanding. The present analysis, almost 20 years subsequent to that by ), represents a return to the broad outlines of the latter, seminal work. Given the different scales of the two analyses in terms of taxa and characters, however, it is unreasonable to assume similarities to be the result of reliance on ‘the same characters’.

An increasing proportion of all studies confirm positions and monophyly of Palaeognathae, Galloanserimorphae and major subclades thereof. However, most molecular studies (e.g.,;;; ), as well as analyses based on combined data, differed significantly with parts of the present hypothesis, especially those pertaining to the Pelecaniformes, Ciconiiformes, Podicipedidae, Opisthocomiformes, Cathartidae, Caprimulgiformes and Coraciiformes (Figs 12–18). There was considerable disagreement among recent molecular studies alone (e.g.;; ), regardless of data analysed, which reveals contrasts only between morphological and molecular inferences to be oversimplifications of modern study (e.g.; ).

Comparisons with the limited number of other analyses (Figs 1–3) were virtually uniformative because palaeontological works have tended to emphasize narrow taxonomic groups considered likely to accommodate newly described or controversial taxa, and also to limit characters to those scoreable for the taxon or fossil of interest (e.g. ), with some exceptions (e.g. ). Several provisional and ongoing reconstructions by ) were not considered here. A survey of comparable cladistic studies of morphological or molecular bases (cf.;;;; ) revealed that the present analysis achieved considerable agreement with most of the latter studies concerning the widely supported (com)positions of the Palaeognathae and Galloanserimorphae, and an allied clade dominated by marine and wading birds (Figs 10–18).

Adjudication of success

It is to be hoped that diverse approaches will converge empirically toward common analytical standards and a solution for which acceptance is widespread and merited. However, there are no standards of accuracy against which phylogenetic analyses of natural lineages can be calibrated (i.e. known histories), and therefore the assessment of progress is elusive. Hypothetico-deductive empiricism may reveal critical characteristics of scientific hypotheses, but cannot provide ‘proof’ of a hypothesis.

Given that proof of hypotheses or certain recognition of the single, true phylogeny is unattainable, the strongest support for a specific reconstruction (beyond intrinsic robustness) lies in common elements shared by other analyses – empirical (not popular) consensus. Such studies are most potent where performed independently using new data. Likelihood of correctness of molecular and morphological reconstructions cannot be judged a priori, especially across all classes of investigation. Such assessments are conditional on individual cases, and decisions based on consistency with prior analyses, degree of resolution (assuming bifurcations are the primary cladogenetic mode), size and diversity of data on which the hypothesis was based, and analytical properties of included characters. The relevance of statistics internal to single trees – e.g. robustness of nodes and consistency indices – to the likelihood of global accuracy is undecided.

Consequently, an important element of phylogenetic study is comparison of findings with the estimates of other investigators, especially comparisons of those aspects of trees that withstand variations in method or data base. However, against which topology or topologies does one compare specific findings? This quandary especially afflicts those disposed to a dichotomous view of morphological and molecular estimates of history. Provision of a sample of trees (Figs 1–9) was intended, in part, to emphasize the dilemma that faces investigators wishing to evaluate hypotheses comparatively. It appears that until some kind of genuine consensus is achieved, systematists are compelled to pit their findings against a plethora of other, marginally comparable works.

Molecular systematics: competitor or collaborator?

At present, molecular systematics is characterized both by the coexistence of general (if not unbridled) optimism and by profound doubts regarding resolution of substantial segments of neornithine phylogeny. Yet the current dominance of avian systematics by molecular methods is sufficiently profound as to lead some to consider palaeontology to be the sole justification for a continued role for morphology in systematics or to question its value altogether (e.g.;;, ). Nevertheless, historical signal from genes and their morphological products offer a potentially fruitful synergy (: 340), one that exceeds the use of morphology for placements of fossils.

An unfortunate pattern has emerged in molecular circles, however, in which perennial problems of avian systematics (Table 1) are attributed to the relative impotence or unreliability of morphological clues to phylogeny (e.g.;;,;;; ), or as justification for merely mapping morphological characters a posteriori onto molecular trees (e.g.;;;; ). Therefore, it would be negligent to forego this opportunity to counter this perception explicitly (e.g.;; ). We do not intend an assault on molecular methodology, but seek to refute persistent prejudices that afflict morphological phylogenetics (cf.; ), to underline the distinctness between ease of application and reliability in phylogenetic methods, and to encourage objectivity in assessment of findings.

Perhaps the deficiency attributed most widely to morphological phylogenetics stems from suspicions of morphological convergence, concerns seldom empirically substantiated and to which molecular methods are widely assumed to be immune. To date, assumptions of morphological convergence principally are made where convenient and are seldom reversed, with few exceptions (e.g.; ). However, verification of convergence in molecular data is increasingly frequent. For morphology, we hope that intuitive claims of convergence will be supplanted by phylogenetically framed analyses of refined morphological and functional data, especially those pertinent to the: pectoral limb; pelvic limb; skull and associated musculature; and general body form.

Studies based both on molecular and morphological phylogenetics (Figs 1–9) manifest substantial disagreement both within and between schools, and remain comparable in resolution and support, with disputes often conjectural in nature. Both classes of data present substantial challenges of homology (further below), and those that face molecular systematists are remarkably similar to those afflicting morphological phylogeneticists. Problems of homology in molecular applications, principally related to ‘gaps’, indels, and their implications for serial homology and sequence alignment, include: bias in substitution and codons; concerted evolution; pseudogenes; silent substitutions and undetected heterogeneity in rates of substitution; selectively constrained evolutionary rates of repetitive DNA families; homoplasy indirectly related to the four-state sampling universe of nucleotides; and independence of molecular ‘characters’.

Similarly, subjectivities of sampling and analysis beset both morphologists and molecular systematists, including: sampling of genes and taxa; comparative weighting; branch support; and model selection. In addition, the critical distinction between ‘gene trees’ and ‘species trees’, which can differ significantly, may be overlooked or ignored.

Despite these considerable challenges, molecular systematics clearly holds great potential for resolution of many problems of avian systematics, particularly in the Passeriformes. An informal survey of the passeriform literature since 1990 revealed studies of diverse taxonomic scales: 11 subordinal, five superfamilial, 34 (sub)familial, 55 generic and 24 (super)specific. This considerable success notwithstanding, largely unexplored is the potential of enterprises jointly including molecular characters of sequence and higher-order genomic structure, the latter ignored at considerable peril. Together with morphological data of fossil and modern taxa, such molecular diversity appears to be essential for progress at many scales of avian phylogeny.

Appeal of the novel and unexpected

Apparent departures from taxonomic groups supported throughout much of the cladistic or molecular eras have been frequent during recent years.: 2570) proposed the entertainment of a number of counter-intuitive and weakly supported groupings in their analysis, in the spirit of freeing systematists from being ‘… guided by preconceptions of relationships.’ The latter appeal for objectivity is unquestionably laudable, but the fact that the proposed groups were merely novel does not constitute affirmation of any kind. Similarly,: 686) stated that their study: ‘… identifies for the first time some sister relationships that had never been suggested before.’[emphasis added]. Although many traditionally recognized higher-order groups deserve formal analysis, novelty of resultant proposals is irrelevant to these endeavours. Realization of this potential primarily turns on two issues of modern systematics – rigorous and nomenclaturally transparent analyses that bridge subdisciplines (beyond the recent penchant to use fossils in molecular phylogenies for estimates of evolutionary rates), and empirically justified views and integration of morphological evidence in an era of increasing reliance on molecular inference.

Insights from avian phylogeny

Hope for success lies in a pluralistic approach to evidence. This goal, in turn, is conditional on the surrender of prejudice and a common concept of homology. Ornithological systematics is replete with assumptions, assertions and inferences concerning homology and its role in the recognition of characters and evolutionary patterns. In practice, variously defined ‘sameness’ is the basis for pre-analytical (a priori) assessments of homology in phylogenetics, but resultant phylogenies provide the historical framework within which homology is confirmed a posteriori. However, non-historical criteria have been attached to the concept of homology virtually since its theoretical origins, of which ontogeny and function were perhaps the most common. Accordingly, alternative perceptions have influenced avian phylogenetics virtually throughout its history, particularly regarding homology and paedomorphic characters, homoplasy and convergence, the concept of Grundplans (e.g. ), and implications of ontogeny and genetics for homology of characters.

Phylogenetics and homology

Homology is synapomorphy at some phylogenetic level, and is defined a priori as ‘similarity due to common descent’ (: 485). ) equated homology with identity (despite change) made evident by phylogeny: homology, reversals, rudimentia, vestigia, atavisms and parallelisms. Considerations of parallelism and convergence for Aves involve aspects of cranial structures among outgroups. Examples of atavism are few, but include the recurrence of a plesiomorphic pelvic muscle among Paradiesidae. Strong examples of morphological parallelism in birds involve the evolutionary loss of flight by flightless Rallidae.

Similarity and homology

Homology is conditional on essential, potentially mutable ‘sameness’ of a character manifesting continuity of descent within a phylogenetic hypothesis, whereas common function and ontogeny are not conditions thereof. ) advocated secondary qualities of generation, integration and autonomy of a structure for the status of homology to be conferred, nuances herein considered components of the essential ‘sameness’, if considered at all. Variants of characters recognized in a phylogenetic context (putative homologues) and manifesting modification with descent – affected by any of a number of mechanisms of evolutionary change (selection, drift, mutation, ontogenetic deviation) – are treated as ‘states’ of a given character here.

Ontogeny and homology

The ontogenetic mechanisms that produce homologous states of a character are of considerable evolutionary interest and may prove critical in particular cases of diagnosis, but do not qualify as criteria of homology of terminal features per se. Genetics of ontogeny, however, can provide unique insights into the bases of likely homologues, e.g. odontogenesis and the edentuly of modern birds.

A synthetic view of homology holds that respective developmental stages of members of lineages, interpreted hierarchically within a phylogenetic framework, are each potential homologues capable of partitioned evolutionary patterns. Thus, homologues are defined within each developmental stage of each character, e.g., genes, developmental processes and stages thereof. However, judgements of homology based on ontogenetic processes are mistaken extensions of identity of descent across quasi-autonomous developmental modules. Traditional assertions that homologues must share genetic foundations represent similar overextensions of historical identity. Variants, including asymmetry, of a terminal character evolved during phylogenetic descent by means of developmental change are homologues of the given character, and variation in the ontogenetic mechanisms behind evolution of the character are not necessarily evidence of non-homology of the resultant states. For practical considerations, predefinitive homologues are problematic for fossil birds as useful fossil embryos are rare.

Developmental sequences include potentially distinct components such as developmental cascades, changes in timing (heterochrony) and position (heterotopy), and frame shifts. Where ontogenetic mechanisms per se are potential characters, the concept of modularity of development implies a delimitation of ontogenetic processes as characters in themselves. Of recent concern is the digital frame-shift within the digiti manus avium, which counters the former embryological hypothesis of ) that is still advocated by ) and ). Subsequent study has implicated Hox genes in such shifts, although the proposal is not without controversy. The modularity of development permits the view of the hypothesis of ) as but one characterization of several plausible candidates based on embryological principles.

Several other instances are variably conspicuous cases of heterochrony – e.g. shifts in general developmental trajectories of Megapodidae and that of the avian furcula. Perceptions regarding the diagnostic relevance of anatomical position with respect to homology vary, e.g. the partly positional argument of the ‘rostro-parasphenoid’ process as distinct from the traditionally defined processus basipterygoideus, typological paradigms, and the role of function. Patterns imposed by altered proximodistal developmental axes of appendages or action of regulatory (e.g. Hox) genes increasingly are recognized in changes among transitional and terminal (definitive) developmental homologues. To date, most references to heterochrony have emphasized paedomorphic characters, i.e. variants of homologues typical of juveniles of plesiomorphic relatives, and include more than simple alteration of growth rates. Instead of undermining homology, such instances of heterochrony provide potentially novel synapomorphies among paedomorphs.

The law of Von Baer – the biogenetic law – postulated that the order of developmental stages in an individual reflects the phylogenetic series of increasingly apomorphic states found in that lineage. In some cases, this series approximates the evolutionary changes leading to the terminal state, and may provide possible insights into polarities and transformation series – i.e. states consistent with the ‘ontogenetic criterion’. Avian candidates for this criterion include the angulus coracoscapularis and mutliple unions of elements or anlagen of the definitive avian shoulder girdle.

Function, homology and convergence

Cladistic (parsimony) analysis often is charged with a disregard for functional implications and convergence of character states, causing systematists to mistake similar but independently derived features among distantly related taxa as homologous. Convergence without demonstrated phylogenetic influence, as well as naive historical examples – e.g. purported affinities of swifts and swallows, tabled decades ago (e.g.;; contra) – do not merit consideration here., ) and ) considered function to be a critical criterion of homology, the independent study of which being required prior to inclusion of the structure in question in a phylogenetic analysis. Notable examples of this paradigm concern specializations of the feeding apparatus of Coraciiformes and Picidae, or cranial refinements among Charadriidae. Hypotheses of homology between features require a phylogenetic framework, and mere similarity of function in two potential homologues fails to demonstrate or exclude homology or convergence.

Convergence frequently is invoked in the context of adaptation and, at least in ornithological tradition, by superficial comparisons of the structures among distantly related lineages that share function, e.g. pelvic limbs of pursuit divers (cormorants, mergansers, loons), forelimbs of wing-propelled divers (alcids, diving petrels, penguins), or bills of piscivores (herons, anhingas, kingfishers). It is notable, however, that phylogenetic relationships among these examples were not obfuscated herein by these analogous similiarities in light of the totality of characters analysed, and that the purported instances of convergence were limited to a minority of phylogenetically analysed characters.

Given that character-states are homologous variants of a particular character defined a priori by critical similarity and a posteriori by continuity of descent, considerations of function, although of evolutionary interest, are not directly germaine to homology or its diagnosis. Function, and its possible relationship to form, constitute but one potential precondition of convergence – one component of homoplasy. Examples of homologues cited independently of ontogeny in birds include: the processus basipterygoideus and modifications for dorsoventral movements of the carpus. Given that homology, and therefore homoplasy, are diagnosed reliably only within a phylogenetic context, non-hierarchical assessments of homoplasy offer few if any insights.

) discussed the differentiation of convergence from parallelism in closely related taxa under the term ‘parallel evolution’, and ) described it in the context of ‘evolutionary homodynamy’. Attribution of taxonomic groupings to convergence is conditional on: (i) the case for homology and plausible selection effecting changes; (ii) reliability of phylogenetic analyses indicating disjunction of the disputed groups; and (iii) the independence of phylogenetic reconstructions from sources of potential bias. Two avian examples follow that might be taken by some to exemplify cases of ‘convergence’ of morphological characters leading to erroneous phylogenetic groups, exercises critical to assessing perceptions relative to empirical evidence.

Ratites. We found strong support for monophyly of ratites, a finding in agreement with current consensus. The prior hypothesis of polyphyly was confounded by a perspective of static continents, convergence and a phenetic emphasis on differences. Synapomorphies of ratites not reasonably related to flightlessness or giantism fail as cladistic support for polyphyly. Finally, advocates of convergence fail to propose an empirically supported, plausible alternative hypothesis of relationship(s) consistent with the morphological (and molecular) data.

In our analysis, no support was found to ally any ratites to other non-ratite taxa; by contrast, 75 characters were ‘diagnostic’ or ‘highly supportive’ of monophyly of ratites (Table 2). Of these, 30 referred to the pectoral girdle or wing. If these 30 characters are accepted to be homologous as coded, they would lend support to the monophyly of ratites and (by parsimony) their shared flightlessness. On the other hand, if analysis had indicated that these same characters were optimized parsimoniously as non-homologous (but not coded a priori as such, absent evidence), the inference would be consistent with the possibility that flightlessness evolved in parallel more than once within a palaeognathous clade. Neither the present phylogeny nor alternative scenarios provide conclusive evidence for hypotheses concerning relative sequence(s) in the evolution of flightlessness in ratites; evolutionary trends of this kind are best explored through optimizations of character-suites a posteriori on the phylogenetic hypothesis (Fig. 13).

Candidates for parallelism of potential phylogenetic influence include the synostosis scapulocoracoideum of ratites and its marked similarity with those of non-avian Theropoda, and convergent enlargement of the angulus coracoscapularis of flightless Neornithes, especially in the ratites and Rallidae. Diagnosis of the scapulocoracoideum as atavism would hinge on the phylogenetic history of the feature. A similar challenge attends classification of other pectoral changes among ratites as plesiomorphy, synapomorphy, parallelism or convergence.

Grebes and loons. We inferred the loons and grebes to be sister taxa, with no comparable support for positioning either taxon more strongly elsewhere (Table 3). Of the 17 characters diagnostic or highly supportive of this relationship (Table 2), 11 are from the pelvic girdle and limb. Those who considered these taxa to be only distantly related typically espoused a certainty that the similarities of the hindlimb and pelvis were misleading convergences associated with foot-propelled diving (: 426;: 5). Suspected convergence is not supported by the differences in the hindlimbs of loons and grebes in that such are at least as parsimoniously interpreted to be: (i) symplesiomorphies differentially lost or modified in the lineages following divergence; or (ii) autapomorphies acquired independently following divergence of the orders. Neither has been shown to be parsimoniously synapomorphic with one or more other avian orders (Fig. 14). It is noteworthy that proponents of an alliance between the grebes and flamingos are tolerant of multiple dissimilarities between the groups. Whatever the scenario, the support index for this couplet of orders (Table 2; Fig. 14) significantly counters a convergent history for these characters, and an alliance with either the Charadriomorphae or the Phoenicopteridae entailed substantial sacrifices in parsimony (Table 3).

Contrasts of ends and means

Until recently the fossil record for birds was marginalized with respect to formal phylogenetics, with most fossil taxa being fragmentary representatives or close relatives of modern groups. A spate of newly discovered fossils from the late Mesozoic has clarified greatly the theropod roots of birds. Despite consensus concerning the phylogenetic implications of new Mesozoic fossils and a number of shared goals, neontological and palaeontological schools often work at cross purposes. A former obstruction to unified analysis was a tradition of speculative evolutionary scenarios with strong palaeontological underpinnings, notably concerning evolutionary transitions and diversification and avifaunal ‘assemblages’, that served as surrogates for ecological data not available for fossil lineages and past eras. A significant convergence in cladistic methods notwithstanding, it remains an unfortunate impediment that goals, expectations, nomenclature and assumptions of avian palaeontologists and neontologists exist in largely parallel circles and have failed to realize a commonality of professional purpose. The most serious analytical challenges posed by avian fossils derive from missing data, which may affect the characters admitted for analysis.

Nomenclatural divergence, analytical corollaries

Issues of strict taxonomy aside, philosophical differences between the subdisciplines also involve long-standing perceptions of the diagnosibility of direct ancestry (e.g.; ). Palaeontological viewpoints regarding ancestral status of fossils also hold implications for nomenclature of fossil lineages (e.g. ‘stem-groups’) in phylogenetics, analytical validity of ‘ghost lineages’, and the evolutionary significance of fossil ‘mosaics’. A neontological perspective, however, considers fossils to differ from modern representatives solely by extinct status and quality of preservation, with many modern lineages representing more informative plesiomorphs of extant clades than any fossil member – e.g. anseriforms Anhimidae, Anseranas vs. fossil Presbyornis. Where adequately preserved for phylogenetic placement, fossils also may provide an estimate of minimal age of the group it represents, but this estimate is imprecise and subject to bias. Ironically, a misunderstanding of such estimation contributed to early arguments concerning ‘temporal incongruence’ and against a theropod origin for birds (e.g., ).

Although the definitions of ‘stem’ and ‘crown’ groups are relatively simple, the former sharing conceptual roots with earlier terms of assumed or possible direct ancestry such as ‘plesions’, it seems that these designations carry important nomenclatural implications and may impede the integration and interpretation of fossil and modern taxa by identical means. Where ancillary assumptions regarding local polarities and implications of ‘stem-group’ members are made in analyses based on narrow samples of taxa (e.g.; ) or characters (e.g.,,,,,;;; ), or if the fossil material is of marginal quality (e.g.,, ), the differences between neontological and palaeontological schools can be substantial. In many contexts, it appears virtually inescapable that ‘stem-group’ status implicitly conserves the notion of possible or likely ancestry relative to the corresponding crown-group, and thereby suggests an evolutionary role beyond mere cladistic position (e.g. successive sister-groups).

Moreover, inclusion of a fossil in a ‘stem-group’ can lead to alternative analytical protocols, e.g. speculations of local polarities and substitution of hypothesized instead of observable character states to lend support to trees including mulitple fossils (e.g.,, ). The comparatively well known Pseudasturidae – formerly assigned to the Family Quercypsittacidae (Psittaciformes) by ) – were judged to combine ‘intermediacy’ in a number of characters purportedly diagnostic of psittaciforms with similarities to the ‘Galbulae’ (Piciformes), and were referred to the ordinal ‘stem-group’ of Psittaciformes by ). Informal hypotheses of polarities in analyses of fossil birds – e.g. by: characters 5 and 12),: characters 1, 6, 11, 29, 35 and 71), and: character 55) – evidently intended to impose ‘local’ initial states in a particular context and often asserted in character descriptions, are innocuous if these are inferred from direct analysis rather than imposed based on preconceptions regarding a taxon. Evidently, however, in some cases states observed for given terminal taxa are replaced by states purportedly representative of ‘stem-group’ members (i.e. states hypothesized to be predecessors to those of taxa included in the corresponding ‘crown group’). Examples of the latter – confirmation of which requires character descriptions and the data matrix – include characters 5, 9, 18, 26, 30 and 68 of ).

A related tradition of avian palaeontology is the imposition of intuitive trends that exceed the strict empirical content of available fossil material. For example, newly discovered fossils – notably a ‘stem-group hummingbird’ (Eurotrochilus inexpectatus) from the early Oligocene of Germany of purportedly modern grade – motivated,,, ) to enter the debate concerning the relationships of the Apodiformes. These efforts included a critique of a description of a fossil taxon by ), the attribution by ) (based on limited taxonomic comparisons) of morphological specializations both for hovering flight and for nectarivory to Eurotrochilus, and speculations on the earliest evidence of avian nectarivory and the coevolution of certain bird-pollinated angiosperms in the New World. Given the oversimplification of distributions of characters, especially within the Apodiformes, and the wider controversy based on molecular data, it is unfortunate that the characters included by,,, ) totalled from 25 to 98, and failed to provide a synthesis of all relevant characters was not provided for relevant taxa prior to speculating regarding graded specializations and coevolutionary trends in the early Cenozoic.

Plesiomorph or interordinal ‘intermediate’?

Perhaps the most prevalent idiosyncracy of palaeontological perspectives is the reputed importance of fossils as a source of phylogenetic ‘bridges’ between extant, comparatively divergent lineages. However, neither the published record nor phylogenetic theory supports this notion, and the role of interordinal ‘linking’ lineages is at least as often revealed by extant taxa. The taxonomic history of Presbyornis illustrates the potential that such expectations may hold for phylogenetic placements of fossils with respect to modern higher-order groups.

) originally described Presbyornis from a single element from the Eocene of western North America as a charadriiform, but later (with abundant additional material) it was asserted to be a ‘transitional’ shorebird and indicative of a close relationship between Charadriiformes and Anseriformes, the intuitive methods employed in the latter being criticized by ). More than a decade later and based on direct cladistic analysis of both Presbyornis and modern taxa, the genus was determined to be a plesiomorphic anatoid. Subsequently, Presbyornis (and synonyms) has been the genus of choice for referral of fossils from the Eocene of England, Eocene of Mongolia, Palaeocene of eastern North America, Cretaceous of Antarctica, late Palaeocene of North America, and Cretaceous of Mongolia.

An examination of the material upon which these referrals were made raises reasonable doubts as to diagnostic reliability, and reveals the role of the comparatively well represented fossil Presbyornis as a palaeontological ‘strange attractor’ for other, variably preserved fossils of uncertain affinities. As the referrals of fossils to the early Anseriformes escalated, purported allies of Presbyornis also increased in number and morphological diversity: ) reported a ‘giant’Presbyornis from the Palaeocene of eastern North America, ) referred a fossil from the mid-Tertiary of Brazil to the Anhimidae; ) phenetically allied Anatalavis from the London Clay to the modern Australian endemic Anseranatidae, a placement disputed by ); ) allied Anserpica from the Oligocene of Europe to the same family; and ) likened Vegavis (Cretaceous of Antarctica) to Presbyornis and referred the genus to the Anatoidea by a nested series of analyses of published data sets, by a method similar to that of supertrees.

The saga of Presbyornis also extended to the interordinal realm of fossil referrals, and provided insights into the alliance formerly alleged between Presbyornis and Phoenicopteridae by way of the poorly understood Juncitarsus, and thereby the subsequently proposed relationship between Phoenicopteridae and Podicipedidae. In addition, ) cited similarities between grebes and the flamingo-like Palaelodidae in the pelvic appendage – the very class of characters considered by many of these authors to be prone to convergence and therefore unreliable in uniting grebes with loons.

Nevertheless,: 140) considered the sister-group relationship between grebes and flamingos to be ‘… one of the best supported higher-level clades within modern birds.’: 523) then suggested that the intermediacy of two skeletal features between Juncitarsus (Eocene of Wyoming) and the Palaelodidae (Oligocene of Europe), fossils traditionally allied to the Phoenicopteridae, ‘… provides a morphological link between Phoenicopteriformes and Podicipediformes.’ As for the early inferences made for Presbyornis, to which Juncitarsus and phoenicopterids were compared, misclassification of fossils can lead to significant errors where informal phenetics and exceptional treatment of fossils are involved, problems not correctable by adoption of empirically depauperate taxonomic nomenclatures (e.g. ‘stems’ and ‘crowns’) and contradictory views on the phylogenetic roles of fossil taxa.

Referrals, old and new

Despite the foregoing critique, well-preserved fossils can provide important insights into avian evolution, especially the Mesozoic origins of the group, and many potentially important fossils currently have yet to be described (J. A. Clarke, pers. comm.) and are beyond the scope of the present work. Unfortunately, a majority of fossil Neornithes, both of Mesozoic and Cenozoic age, were named based on material not permitting meaningful inclusion in a formal cladistic analysis of modern scale. Moreover, classifications of many of these taxa were made phenetically, and with a marked tendency to refer new taxa to the modern taxon perceived to be most similar. Fortunately, increased use of cladistic analyses makes it likely that such records, especially those spanning the late Mesozoic and early Cenozoic, will provide an increasingly refined palaeontological dimension to avian phylogenetics.

Given the limitations of direct diagnosis (Table 2) and the phenetics of seeking the best neornithine group in which to place a fossil, what is the recommended means for evaluation of a new fossil with respect to the present data set? Two paths seem most informative at present: (i) unconstrained analysis of the present data set, appended with the codings for the fossil taxon, however incomplete (within reasonable limits of informativeness); or (ii) analysis of the fossil taxon under a backbone-constraint for modern lineages (e.g. Figs 13–18). The latter probably will prove optimal in those cases where missing data are especially numerous or where even higher-order affinities are indiscernible, and especially where both circumstances pertain. Taxonomic groups of greatest diversity and quality of preservation hold the greatest potential for such insights, and these merit special emphasis here, especially those broadly consistent with groupings inferred here and for groups having few modern members.

Diversity, aquatic and terrestrial

Fossils have been referred, although not all by phylogenetic means, to all modern families of the Pelecaniformes: Phaethontidae, Fregatidae, Fregatidae or Sulidae, Sulidae, Pelecanidae, Phalacrocoracidae and Anhingidae. In addition, the controversially referred Plotopteridae have increased in palaeodiversity. Less well justified is the putative membership of a group of widespread, fossil, pseudo-denticulate birds – Odontopterygiformes – for which a modest analysis mustered marginal support as an alternative sister-group to the Anseriformes.

The Coliiformes, Trogoniformes, Coraciiformes and Piciformes merit renewed examination as these groups (e.g. Bucconidae sensu lato, including Primobucconidae), as well as specimens of uncertain affinity, also have received multiple new fossil referrals – including Trogoniformes, Coliiformes, Coraciiformes and Piciformes. Broadly delimited zygodactyl taxa complete the apparent palaeodiversity of ‘higher’ landbirds (Fig. 18), and contrasts with modern passeriform dominance.

The Psittaciformes, at least the modern members of which are anatomically distinctive, have attracted a number of newly described fossils, some of which obscure this distinctness, and thus the order has undergone pronounced extensions of its palaeodistributional limits. The uniquely apomorphic form of the crania of some taxa in this order is so extreme as to pose challenges of comparability, and many modern members also manifest distinctly modified pectoral girdles and apomorphic pelvic skeletons. However, some fragments controversially referred to this clade are of potential relevance to the origins of modern orders and the K–T boundary ( vs. ), and merit reassessment.

Preservation and inferred distribution

A traditional referral of issues of ‘deep time’ to palaeontology evidently reflects, in part, the rapidity with which fossil evidence was conjoined with modern phylogenetics for the calibration of geological time with phylogenetic hypotheses. Palaeocalibration of ages provided by fossil records in combination with models of molecular phylogenetics predictably turns on taxonomic groups possessed of rich, accurately aged fossils and reliable phylogenies.

These cross-disciplinary works progressed (perhaps too) rapidly toward attempts at global treatments of Neornithes that were influenced by undue inclusion of fossils of unreliable identity and age. In addition, the early spate of efforts favoured classes of models (e.g. Markovian) that facilitate minimization or ‘smoothing’ of discrepancies between calibrations and branching patterns as opposed to realistic incorporation of heterogeneous evolutionary rates. The latter, often underappreciated, reality reflects the likelihood of preservation and a negative skewness of such records expected to be inversely correlated with body size and related heteroscedasticity that is directly correlated with geological age. These palaeontological issues are confounded by unrealistic assumptions of molecular trees and models in which the fossil data are incorporated. Not surprisingly, informativeness of such exercises to date has been limited – i.e. modern orders have been inferred to have very early origins (: table 1;: tables 1, 2). Nevertheless, a phylogenetic hypothesis of high support and resolution (Figs 10–18) is an essential starting point – one, however, conditional on independent testing and augmentation. Another precondition of success, aside from well-documented fossil records (e.g. ), is use of realistic assumptions regarding molecular evolution where calibration of ages of divergence events is among the objectives.

Calibration of time

Failure to verify the existence of a molecular ‘clock’ notwithstanding, an endeavour of particular interest regards bringing to bear the calibration of geological time – the ‘time axis’ of ) – through phylogenetically placed fossil taxa, thereby estimating a minimal age of corresponding nodes in a phylogeny and recavering the temporal pattern of avian diversification. Direct use of stratigraphic data for inference of trees by means of parsimony or ‘stratocladistics’ has been criticized on several methodological grounds, and is especially inappropriate for the sparse avian fossil record.

Well-supported phylogenies for molecular models are critical for extrapolations of evolutionary rates from fossil-based point-estimates of geological age. Disagreements among calibrations to date are consistent with evidence for significant variation among rates of evolution, the effects of outgroups, initial estimates of which (e.g. ) continue to be used. Other problems stem from the limited suitability of stratigraphic data in phylogenetic contexts, and effects of topological aspects of trees. The continued controversy concerning the position of the Passeriformes relative to other Neoaves (especially Fig. 10) – considered by many to reflect effects of outgroup and relative evolutionary rates of mtDNA – presents a critical issue for attempts at calibrations more precise than Mesozoic vs. Cenozoic origins.

Accordingly, the prospect of using currently available palaeontological data to calibrate evolutionary rates is disconcerting, regardless of the phylogenetic framework conjoined, principally because of a paucity of fossils that are reliably classified and of precise age. However, the existence of avian lineages in the late Mesozoic has been substantiated directly by palaeontological evidence. For example, the estimated origin of megapodiid galliforms in the Cretaceous agrees well with estimates for the comparably ancient Anseriformes.

Special attention relates to the oldest fossil record for a member of the Neornithes, increasingly with respect to hypotheses of descent relative to massive faunal upheavals following the K–T boundary. Despite considerable effort, few points of agreement among phylogenetic calibration of rates and fossil records have been achieved. In part, disagreements reflect variable reliances on assumpitions of ‘clock-like’ molecular evolution. The unrealistic assumption of ‘clock-like’ molecular change has led to diverse means of ‘correction’ or analytical adjustments, increased sampling of fossils, incorporation of multiple ‘clocks’ and relaxation of estimators through Bayesian methods.

For example, ) stated that the earliest passeriform is no older than the early Oligocene, whereas ) inferred the order to have originated prior to the K–T boundary, a discrepancy of magnitude likely to weaken associated calibrations. Recent attempts to bracket times of avian cladogenesis by: fig. 3) based on the few widely accepted higher-order relationships necessarily encompassed relatively few major lineages of birds, whereas a priority accorded expanded taxonomic samples led ) to accept calibrations based on many fossils classified from the literature, relationships derived from the phenetics of DNA hybridization, and a null model incorporating questionable assumptions concerning molecular evolution and a basal polytomy for Neoaves.

Palaeobiogeography and the spatial dimension

There is considerable optimism bestowed upon fossil taxa for the reconstruction of historical biogeography. Southern-hemispheric patterns interpreted in terms of tectonic fragmentation and movements are manifested in the literature of avian systematics. Realistic reconstructions of historical biogeography require effects of vicariance events within continents – e.g. mountainous uplifts or glaciation – as a secondary class of abiotic antecedants of phylogenetic diversification.

Of greater empirical substance for Aves, perhaps, are inferences of historical vicariance, notably those fortified by robust phylogenetic analyses and showing congruent geographical patterns. Most important of these for birds is the recurrent pattern of southern origins among many lineages, collectively suggestive of a critical role for Gondwana in early avian origins and diversification and most strikingly coincident with the K–T boundary. Patterns consistent with southern genesis are especially compelling in light of a biased tendency for migratory habit to counter northern–southern hemispheric patterns relative to those of eastern–western hemispheres. Taxa for which circumstantial evidence of this kind is consistent with southern-hemispheric origins, include: Ratitae, Anseriformes, Galliformes, Sphenisciformes, Gruiformes, Psittaciformes, Trochilidae and suboscine Passeriformes.

The Palaearctic understandably dominated palaeogeographical hypotheses in the early 20th century, especially for fossils from the late Cenozoic. The prevalence of terrestrial groups during the Palaeogene considered ‘basal’ to the Passeriformes (i.e. branching from the lineage culminating in the Passeriformes and its sister-group) prompted ) to suggest that the former taxa may have occupied ‘passeriform’ niches prior to the Oligocene. This hypothesis should be amenable to testing by morphological comparisons but is contingent on the resolution of debated dates of origin of the Passeriformes. Among the avian clades most frequently cited with respect to adaptive radiation, key innovation, ontogenetic underpinnings and sheer diversity – phenomena of prime interest – are the Apodiformes and Passeriformes. Accordingly, the Apodiformes (especially the Trochilidae) attracted substantial anatomical and phylogenetic study. The Passeriformes, however, hold a position of unique diversity – comprising 60% of extant Aves and unmatched global distribution, evolutionary success and adaptation.

Evolutionary radiations and the K-T controversy

Such palaeogeographical patterns have shed light on the theory of ‘adaptive radiation’, ‘explosive radiation’, and ‘mass extinction’ of Aves around the K–T boundary. Other biogeographical hypotheses of significance relate cladogenetic patterns and faunal diversity to tectonic movements, and trans-Gondwanan dispersal.

In particular, the Charadriiformes have been the focus of substantial, speculative scenarios regarding a special evolutionary role involving multiple avian groups and major extinctions. The notion that ‘shorebirds’ are fundamental to an understanding of avian evolution across the K–T boundary is no longer considered promising, and was based in part on a preconception of Charadriiformes as phenotypic intermediates bridging higher-order avian groups.

Quantitative estimation of rates of evolutionary change – given robust phylogenies and adequate fossil records – have fostered more detailed hypotheses of phylogenetic bottlenecks and ‘explosive’ radiation near the K–T boundary (,; but see ). However, there is growing evidence, at least based on Bayesian analyses of data largely or entirely from the mitochondrial genome, that most or all neornithine orders date from the late Cretaceous. If accurate, despite the vulnerability of such data to suboptimal rooting, this record undermines early anticipations of K–T boundary effects in modern orders and an evolutionary timespan in which major divergences of neornithine lineages would extend through the early and middle Cenozoic. Expectations for avian fossils of such antiquity are correspondingly conservative, and although fossils of such age potentially offer new calibration points for early avian lineages, there is diminished hope for points of calibration bearing on the relative antiquity of modern (super)orders of birds or precise molecular estimates of associated evolutionary rates characteristic of phylogenetic lineages.

Current points of irresolution

Based on the present analysis (Figs 1–8) and other studies during recent decades (Figs 10–18), the area of primary ignorance for avian phylogenetics is the heretofore refractory groupings within the Neoaves, with principal problems being the highest-level nodes (notably the position of the Passeriformes within this group) and the comparatively routine but significant work of phylogeny within orders and families (Fig. 11; Appendix 1). Optimism remains justified, however, with new genes and molecular signal of scale higher than simple sequences and indels under exploration (e.g. retroposons). Reliance solely on a single scale of homology, e.g. the indels upon which ) proposed largely hemisperically concordant ‘Metaves’ and ‘Coronaves’, is herein inferred to be nomina nuda (Appendix 1). This fixation on single-scale molecular analyses justifiably led: 42) to ask: ‘Can four million bases [nucleotides] resolve the [avian] tree?’ Fortunately, there are a number of anatomical fields of study that remain virtually untouched in modern phylogenetic contexts, a circumstance of hope in light of the palaeontological discoveries that will necessitate refinement of these and refined anatomical complexes coded (e.g. os palatinum of Archaeopteryx;; ).

Several episodes of avian phylogeny were incompletely resolved in the present analysis (Figs 12–18), and will require significantly intensified sampling of taxa to solve:

Positions of Aepyornithiformes and Dinornithiformes relative to extant ratites (Fig. 13).

Resolution of genera within the Phasianoidea (Fig. 13).

Resolution of the positions of the Psittaciformes and Columbiformes (Figs 16, 17).

Determination of the relationships among several poorly resolved nodes involving the traditional Charadriiformes and Gruiformes, within the ‘central’ Charadriiformes (Fig. 15), for which alternative proposals continue to appear, a task likely to require inclusion of rich suites of such integumentary characters as the natal integument for reconstruction of deeper nodes, and aspects of the definitive externum for resolution of shallower nodes.

Confirmation of relationships of the families of Caprimulgiformes (Fig. 17).

Resolution of the trichotomy among the Coraciiformes, Piciformes and Passeriformes (Figs 17, 18), and resolution of subordinal and familial phylogeny within the Passeriformes, and affirming the position of the Passeriformes relative to other Neoaves.

Make available an empirically grounded platform for finer-scale analyses of single orders or families of Neornithes as an alternative to the classical literature or the ‘tapestry’ by ), with priority accorded to comparatively old, multifamilial orders (e.g. Galliformes, Procellariiformes) or traditionally challenging groups (e.g. Pelecanimorphae).

Phylogenetic integration of well-preserved fossils into the phylogeny, both serving as additional taxa for resolution or revision of groups and as points of calibration of (minimal) ages of lineages of which these are members.

An especially rewarding class of study awaits optimization of life-historical attributes at the present phylogenetic scale, attributes such as sexual dimorphism, parental care and reproductive parameters as a starting point for more detailed studies in evolutionary biology. This area of study can advance only with: (i) use of well-resolved, robustly supported phylogenies, often not feasible (e.g. ); and (ii) refinement of methods for optimization a posteriori of attributes, including where phylogenies include polytomies.

An unfortunate aspect of such methods has been revealed by a number of optimizations that relied on the phenetics of ), ostensibly as it was the only hypothesis of adequate taxonomic breadth for the desired survey (e.g. ). Attributes so assessed include body mass, wing length and correlates of flightlessness. Most such published surveys have recovered significant patterns in selected morphological attributes despite the virtually universal view that the quasi-phylogeny that was used is unreliable. This incongruity indicates that apparent significance of optimizations is essentially meaningless, but more importantly provided a fortuitous insight that statistically significant patterns can emerge from inaccurate phylogenetic hypotheses and that it may be prudent to adopt more conservative critical values for tests of this nature. Until more discriminating methods are available, significance in this context should not be assessed against a null model of random change but instead against randomized evolution with varied descent or reserved for comparisons between phylogenies.

Broadened phylogenetic horizons

) entitled their paper with a challenge of undisputed cogency: ‘How good are deep phylogenetic trees?’ An expansion of phylogenetics of the Theropoda and Dinosauria is well underway, however, and will be central to a robust foundation for avian phylogeny, including significant implications for ‘global’ homology and anatomical nomenclature. This exploration should lead to phylogenetic hypotheses among Vertebrata of increasing scale, especially in light of character analyses already accomplished for non-avian Tetrapoda. Similar explorations among deep roots by molecular and morphological means also hold promise for the phylogenetic resolution of an expanded ‘super-clade’ of Reptilia and allied Tetrapoda, including (sub)fossil taxa to the degree permitted by remains and logistic limits on life-historical data available for fossil taxa. In contrast to issues of quality of the fossil record and limits on signal recoverable from fossils, potential for neontological study remains underexplored, especially that involving soft-tissue anatomical systems.

In light of the evident attraction of probabilistic reconstructions, phylogenetics may benefit most from an expansion of Bayesian methods to address problems of incomplete data, robustness of estimates and refined optimization, including (quasi-)likelihood methods, both parametric and non-parametric. In both major classes of probabilistic models, renewed attention is justified to the analytical properties of branching processes, for which statistical methods have been elaborated only recently. In a problem of this unprecedented scale, it is critical for modern systematists to exploit a diversity of sources of data as a means to effect even-handed assessments of historical pattern.

An overview of the literature (Figs 1–10) reveals that much remains to be accomplished in avian phylogenetics. Significant advances principally lie in studies of great taxonomic scale and diverse support that target nodes of ordinal and higher taxonomic scales of Neoaves, in conjunction with a solution of the persistent disputes among morphological, mitogenomic and nuclear findings. In combination with incorporation of additional, evolutionarily conservative characters of soft anatomy and karyotypes, the methods of ‘total-evidence’ analyses hold promise for phylogenetic scales and calibration of ages previously not feasible, a potential not without early tests (e.g. ) and new methodological challenges.

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    Johnson KP, Goodman SM, Lanyon SM. A phylogenetic study of the Malagasy couas with insights into cuckoo relationships. Molecular Phylogenetics and Evolution. 2000;14:436-444.

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    Johnson KP, Sorenson MD. Phylogeny and biogeography of dabbling ducks (genus Anas): a comparison of molecular and morphological characters. Auk. 1999;116:792-805.

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  529. 529.

    Lanyon SM, Hall JG. Reexamination of barbet monophyly using mitochondrial-DNA sequence data. Auk. 1994;111:389-397.

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  530. 530.

    Lanyon SM, Zink RM. Genetic variation in piciform birds: monophyly and generic and familial relationships. Auk. 1987;104:724-732.

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  539. 539.

    Lee PLM, Clayton DH, Griffiths R, Page RDM. Does behavior reflect phylogeny in swiftlets (Aves: Apodidae)? A test using cytochrome b mitochondrial DNA sequences. Proceedings of the National Academy of Science USA. 1996;93:7091-7096.

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  540. 540.

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    Lee K, Feinstein J, Cracraft J, Mindell DP. Phylogenetic relationships of the ratite birds: resolving conflicts between molecular and morphological data sets. Avian molecular evolution and systematics. 1997;173-211.

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    Lee MSY, Hugall AF. Model type, implicit weighting, and model averaging in phylogenetics. Molecular Phylogenetics and Evolution. 2005;38:847-857.

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    Leeton PRJ, Christidis L, Westerman M, Boles WE. Molecular phylogenetic affinities of the night parrot (Geopsittacus occidentalis) and the ground parrot (Pezoporus wallicus). Auk. 1994;111:833-843.

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    Leonard L, Dyke GJ, Van Tuinen M. A new specimen of the fossil palaeognath Lithornis from the Lower Eocene of Denmark. American Museum Novitates. 2005;3491:1-11.

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    Lerner HRL, Mindell DP. Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution. 2005;37:327-346.

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    Ligon JD. Relationships of the cathartid vultures. University of Michigan, Museum of Zoology Occasional Paper. 1967;651:1-26.

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    Ligon JD. The evolution of avian breeding systems. 1999.

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    Lipscomb DL. Parsimony, homology and the analysis of multistate characters. Cladistics. 1992;8:45-65.

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  551. 551.

    Livezey BC. A phylogenetic analysis of Recent anseriform genera using morphological characters. Auk. 1986;105:681-698.

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  552. 552.

    Livezey BC. Morphometrics of flightlessness in the Alcidae. Auk. 1988;105:681-698.

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  553. 553.

    Livezey BC. Morphometric patterns in Recent and fossil penguins (Aves, Sphenisciformes). Journal of Zoology (London). 1989a;219:269-307.

    Not in our library10.1111/j.1469-7998.1989.tb02582.x

  554. 554.

    Livezey BC. Flightlessness in grebes (Aves, Podicipedidae): its independent evolution in three genera. Evolution. 1989b;43:29-54.

    Not in our library10.1111/j.1558-5646.1989.tb04205.x

  555. 555.

    Livezey BC. Phylogenetic relationships and incipient flightlessness of the extinct Auckland Islands merganser. Wilson Bulletin. 1989c;101:410-435.

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  556. 556.

    Livezey BC. Evolutionary morphology of flightlessness in the Auckland Islands Teal. Condor. 1990;92:639-673.

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  557. 557.

    Livezey BC. A phylogenetic analysis and classification of Recent dabbling ducks (Tribe Anatini) based on comparative morphology. Auk. 1991;108:471-508.

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  558. 558.

    Livezey BC. Morphological corollaries and ecological implications of flightlessness in the kakapo (Psittaciformes: Strigops habroptilus). Journal of Morphology. 1992a;213:105-145.

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  559. 559.

    Livezey BC. Flightlessness in the Galápagos cormorant (Compsohalieus[Nannopterum]harrisi): heterochrony, giantism, and specialization. Zoological Journal of the Linnean Society. 1992b;105:155-224.

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  560. 560.

    Livezey BC. An ecomorphological review of the dodo (Raphus cucullatus) and solitaire (Pezophaps solitaria), flightless Columbiformes of the Mascarene Islands. Journal of Zoology (London). 1993;230:247-292.

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  561. 561.

    Livezey BC. The carpometacarpus of Aptornis[sic]. Notornis. 1994;41:51-60.

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  562. 562.

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    Livezey BC. A phylogenetic analysis of the whistling and white-backed ducks (Anatidae: Dendrocygninae) using morphological characters. Annals of Carnegie Museum. 1995b;64:65-97.

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  564. 564.

    Livezey BC. Phylogeny and evolutionary ecology of modern seaducks (Anatidae: Mergini). Condor. 1995c;97:233-255.

    Not in our library

  565. 565.

    Livezey BC. Phylogeny and comparative ecology of stiff-tailed Ducks (Anatidae: Oxyurini). Wilson Bulletin. 1995d;107:214-234.

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  566. 566.

    Livezey BC. A phylogenetic analysis of the geese and swans (Anseriformes: Anserinae), including selected fossil species. Systematic Biology. 1996a;45:415-450.

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  567. 567.

    Livezey BC. A phylogenetic reassessment of the tadornine-anatine divergence (Aves: Anseriformes, Anatidae). Annals of Carnegie Museum. 1996b;65:27-88.

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  568. 568.

    Livezey BC. A phylogenetic analysis of modern pochards (Anatidae: Aythyini). Auk. 1996c;113:74-93.

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  569. 569.

    Livezey BC. A phylogenetic analysis of basal Anseriformes, the fossil Presbyornis, and the interordinal relationships of waterfowl. Zoological Journal of the Linnean Society. 1997a;121:361-428.

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    Livezey BC. An annotated phylogenetic classification of waterfowl (Aves: Anseriformes), including selected fossil species. Annals of Carnegie Museum. 1997b;67:457-496.

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    Livezey BC. A phylogenetic analysis of modern shelducks and sheldgeese (Anatidae, Tadornini). Ibis. 1997c;139:51-66.

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    Livezey BC. Erratum – A phylogenetic analysis of basal Anseriformes, the fossil Presbyornis, and the interordinal relationships of waterfowl. Zoological Journal of the Linnean Society. 1998a;124:397-398.

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    Livezey BC. A phylogenetic analysis of the Gruiformes (Aves) based on morphological characters, with an emphasis on the rails (Rallidae). Philosophical Transactions of the Royal Society (Series B). 1998b;353:2077-2151.

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    Livezey BC. Avian spirit collections: attitudes, importance and prospects. Bulletin of the British Ornithologists’ Club. 2003a;123(Suppl.):35-51.

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  575. 575.

    Livezey BC. Evolution of flightlessness in rails (Gruiformes: Rallidae): phylogenetic, ecomorphological, and ontogenetic perspectives. Ornithological Monographs. 2003b;53:1-654.

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  576. 576.

    Livezey BC. Millenial status report as debate wanes [review]. Science. 2003c;299:1664-1665.

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  577. 577.

    Livezey BC, Humphrey PC. Flightlessness in steamer-ducks (Anatidae: Tachyeres): its morphological bases and probable evolution. Evolution. 1986;40:540-558.

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  578. 578.

    Livezey BC, Martin LD. The systematic position of the Miocene anatid Anas[?]blanchardi Milne-Edwards. Journal of Vertebrate Paleontology. 1988;8:196-211.

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    Livezey BC, Zusi RL. Higher-order phylogenetics of modern Aves based on comparative anatomy. Netherlands Journal of Zoology. 2001;51:179-206.

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    Livezey BC, Zusi RL. Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy: I. – Methods and characters. Bulletin of the Carnegie Museum of Natural History. 2006;37:1-556.

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    Lockhart PJ, Steel MA, Hendy MD, Penny D. Recovering evolutionary trees under a more realistic model of sequence evolution. Molecular Biology and Evolution. 1994;11:605-612.

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    Lowe PR. On the significance of certain characters in some charadriine genera, with a provisional classification of the order Charadriiformes. Ibis. 1922;64:475-495.

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  583. 583.

    Lowe PR. Notes on the systematic position of Ortyxelus, together with some remarks on the relationships of the turnicomorphs and the position of the seed-snipe (Thinocoridæ) and sand-grouse. Ibis. 1923;65:276-299.

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  584. 584.

    Lowe PR. On the anatomy and systematic position of the Madagascan bird Mesites (Mesœnas), with a preliminary note on the osteology of Monias. Proceedings of the Zoological Society of London. 1924;1924:1131-1152.

    Not in our library

  585. 585.

    Lowe PR. (1) On the systematic position of the Jacanidæ (Jaçanás), with some notes on a hitherto unconsidered anatomical character of apparent taxonomic value, (2) a preliminary note on the classification of the Charadriiformes (Limicolæ and Laro-Limicolæ) based on this character, viz., the morphology of the quadrato-tympanic articulation. Ibis. 1925;67:132-147.

    Not in our library

  586. 586.

    Lowe PR. Studies and observations bearing on the phylogeny of the ostrich and its allies. Proceedings of the Zoological Society of London. 1928;1928:185-247.

    Not in our library

  587. 587.

    Lowe PR. On the relationships of the Æpyornithes to the other Struthiones as revealed by a study of the pelvis of Mullerornis. Ibis. 1930;72:470-490.

    Not in our library

  588. 588.

    Lowe PR. An anatomical review of the ‘waders’ (Telmatomorphæ), with special reference to the families, subfamilies, and genera within the suborders Limicolæ, Grui-Limicolæ and Lari-Limicolæ. Ibis. 1931a;73:712-771.

    Not in our library

  589. 589.

    Lowe PR. On the relations of the Gruimorphæ to the Charadriimorphæ and Rallimorphæ, with special reference to the taxonomic position of Rostratulidæ, Jacanidæ, and Burhinidæ (Œdicnemidæ olim), with a suggested new order (Telmatomorphæ). Ibis. 1931b;73:491-534.

    Not in our library

  590. 590.

    Lowe PR. On the primitive characters of the penguins, and their bearing on the phylogeny of birds. Proceedings of the Zoological Society of London. 1933;102:483-541.

    Not in our library

  591. 591.

    Lowe PR. On the relationships of the Struthiones to the dinosaurs and the rest of the avian class, with special reference to the position of Archaeopteryx. Ibis. 1935;77:298-429.

    Not in our library

  592. 592.

    Lowe PR. On the systematic position of the swifts (Suborder Cypseli) and hummingbirds (Suborder Trochili), with special reference to their relation to the order Passeriformes. Transactions of the Zoological Society of London. 1939;24:307-348.

    Not in our library

  593. 593.

    Lowe PR. Some additional anatomical factors bearing on the phylogeny of the Struthiones. Proceedings of the Zoological Society of London. 1942;112:1-20.

    Not in our library

  594. 594.

    Lowe PR. Some notes on the anatomical differences obtaining between the Cuculidæ and the Musophagidæ, with special reference to the specialization of the œsophagus in Cuculus canorus Linnæus. Ibis. 1943;85:490-515.

    Not in our library

  595. 595.

    Lowe PR. Some additional comments on the phylogeny of the Struthiones. Ibis. 1944a;86:37-42.

    Not in our library

  596. 596.

    Lowe PR. An analysis of the characters of Archæopteryx and Archæornis. Were they reptiles or birds? Ibis. 1944b;86:517-543.

    Not in our library

  597. 597.

    Lowe PR. On the systematic position of the woodpeckers (Pici), honey-guides (Indicator), hoopoes and others. Ibis. 1946;88:103-127.

    Not in our library

  598. 598.

    Lowe PR. What are the Coraciiformes? Ibis. 1948;90:572-582.

    Not in our library

  599. 599.

    Lucchini V, Hoglund J, Klaus S, Swenson J, Randi E. Historical biogeography and mitochondrial DNA phylogeny of grouse and ptarmigan. Molecular Phylogenetics and Evolution. 2001;20:149-162.

    Not in our library10.1006/mpev.2001.0943

  600. 600.

    Lyons-Weiler J, Hoelzer GA. Escaping from the Felsenstein zone by detecting long branches in phylogenetic data. Molecular Phylogenetics and Evolution. 1997;8:375-384.

    Not in our library10.1006/mpev.1997.0450

  601. 601.

    Lyons-Weiler J, Hoelzer GA, Tausch RJ. Optimal outgroup analysis. Biological Journal of the Linnean Society. 1998;64:493-511.

    Not in our library

  602. 602.

    Mabee PM, Wiens JJ. The usefulness of ontogeny in interpreting morphological characters. Phylogenetic analysis of morphological data. 2000;84-114.

    Not in our library

  603. 603.

    Maddison DR. The discovery and importance of multiple islands of most-parsimonious trees. Systematic Zoology. 1991;40:315-328.

    Not in our library

  604. 604.

    Maddison WP. Missing data versus missing characters in phylogenetic analysis. Systematic Biology. 1993;42:576-581.

    Not in our library

  605. 605.

    Maddison WP. Gene trees in species trees. Systematic Biology. 1997;46:523-536.

    Not in our library

  606. 606.

    Maddison WP, Donoghue MJ, Maddison DR. Outgroup analysis and parsimony. Systematic Zoology. 1984;33:83-103.

    Not in our library

  607. 607.

    Maddison WP, Maddison DR. MacClade. 1992.

    Not in our library

  608. 608.

    Manegold A. Zur Phylogenie und Evolution dere ‘Racken’-, Specht-, und Sperlingsvögel (‘Coraciiformes’, Piciformes und Passeriformes: Aves). 2005.

    Not in our library

  609. 609.

    Manegold A, Mayr G, Mourer-Chauviré C. Miocene songbirds and the composition of the European passeriform avifauna. Auk. 2004;121:1155-1160.

    Not in our library

  610. 610.

    Marceliano MLV. Estudo osteológico e miológico do crânio de Opisthocomus hoazin (Müller, 1776) (Aves: Opisthocomidae), comparado com algumas espécies de Cracidae, Musophagidae e Cuculidae. Boletim do Museum Paraense Emílio Goeldi (Série Zoologia). 1996;12:95-246.

    Not in our library

  611. 611.

    Mariaux J, Braun MJ. A molecular phylogenetic survey of the nightjars and allies (Caprimulgiformes) with special emphasis on the potoos (Nyctibiidae). Molecular Phylogenetics and Evolution. 1996;6:228-244.

    Not in our library10.1006/mpev.1996.0073

  612. 612.

    Marks BD, Willard DE. Phylogenetic relationships of the Madagascan pygmy kingfisher (Ispidina madagascariensis). Auk. 2005;122:1271-1280.

    Not in our library

  613. 613.

    Marques AC, Gnaspini P. The problem of characters susceptible to parallel evolution in phylogenetic reconstructions: suggestion of a practical method and its application to cave animals. Cladistics. 2001;17:371-381.

    Not in our library

  614. 614.

    Marshall JT. Relationships of certain owls around the Pacific. Natural History Bulletin of the Siam Society. 1966;21:235-242.

    Not in our library

  615. 615.

    Marshall CR. The fossil record and estimating divergence times between lineages: maximum divergence times and the importance of reliable phylogenies. Journal of Molecular Evolution. 1990;30:400-408.

    Not in our library10.1007/bf02101112

  616. 616.

    Martin LD, Brush AH, Clarke GA. Origin and early evolution of birds. Perspectives in ornithology: essays presented for the centennial of the American Ornithologists’ Union. 1983;291-353.

    Not in our library

  617. 617.

    Maryanska T, Osmólska H, Wolsan M. Avialian status for Oviraptorosauria. Acta Palaeontologica Polonica. 2002;42:361-371.

    Not in our library

  618. 618.

    Maurer BA. The evolution of body size in birds. I. Evidence for non-random diversification. Evolutionary Ecology. 1998;12:925-934.

    Not in our library

  619. 619.

    Maurer DR, Raikow RJ. Appendicular myology, phylogeny, and classification of the avian order Coraciiformes (including Trogoniformes). Annals of Carnegie Museum. 1981;50:417-434.

    Not in our library

  620. 620.

    Mayr E. The sequence of songbird families. Condor. 1958;60:194-195.

    Not in our library

  621. 621.

    Mayr G. Ein Archaeotrogon (Aves: Archaeotronidae) aus dem Mittel-Eozän der Grube Messel (Hessen, Deutschland)? Journal of Ornithology. 1998a;139:121-129.

    Not in our library

  622. 622.

    Mayr G. ‘Coraciiforme’ und ‘piciforme’ Kleinvögel aus dem Mittel-Eozän der Grube Messel (Hessen, Deutschland). Courier Forschungsinstitut Senckenberg. 1998b;205:1-101.

    Not in our library

  623. 623.

    Mayr G. A new family of Eocene zygodactyl birds. Senckenbergiana Lethaea. 1998c;78:199-209.

    Not in our library

  624. 624.

    Mayr G. A new trogon from the middle Oligocene of Céreste, France. Auk. 1999a;116:427-434.

    Not in our library

  625. 625.

    Mayr G. Caprimulgiform birds from the Middle Eocene of Messel (Hessen, Germany). Journal of Vertebrate Paleontology. 1999b;19:521-532.

    Not in our library

  626. 626.

    Mayr G. A new raptor-like bird from the lower Eocene of North America and Europe. Senckenbergiana Lethaea. 2000a;80:59-65.

    Not in our library

  627. 627.

    Mayr G. A new mousebird (Coliiformes: Coliidae) from the Oligocene of Germany. Journal of Ornithology. 2000b;141:85-92.

    Not in our library

  628. 628.

    Mayr G. New or previously unrecorded avian taxa from the middle Eocene of Messel (Hessen, Germany). Mitteilungen aus dem. Museum Naturkunde in Berlin (Geowissenschaftliche Reihe). 2000c;3:207-219.

    Not in our library

  629. 629.

    Mayr G. Tiny hoopoe-like birds from the middle Eocene of Messel (Germany). Auk. 2000d;117:964-970.

    Not in our library

  630. 630.

    Mayr G. New specimens of the middle Eocene fossil mousebird Selmes absurdipes Peters 1999. Ibis. 2001a;143:427-434.

    Not in our library

  631. 631.

    Mayr G. A second skeleton of the early Oligocene trogon Primotrogon wintersteini Mayr 1999 (Aves: Trogoniformes: Trogonidae) in an unusual state of preservation. Senckenbergiana Lethaea. 2001b;81:335-338.

    Not in our library

  632. 632.

    Mayr G. A cormorant from the late Oligocene of Enspel, Germany (Aves, Pelecaniformes, Phalacrocoracidae). Senckenbergiana Lethaea. 2001c;81:329-333.

    Not in our library

  633. 633.

    Mayr G. The earliest fossil record of a modern-type piciform from the late Oligocene of Germany. Journal of Ornithology. 2001d;142:2-6.

    Not in our library

  634. 634.

    Mayr G. A new specimen of the tiny middle Eocene bird Gracilitarsus mirabilis (New Family: Gracilitarsidae). Condor. 2001e;103:78-84.

    Not in our library

  635. 635.

    Mayr G. The relationships of fossil apodiform birds – a comment on Dyke (2001). Senckenbergiana Lethaea. 2001f;81:1-2.

    Not in our library

  636. 636.

    Mayr G. Comments on the systematic position of the putative Lower Eocene parrot Pulchrapollia gracilis. Senckenbergiana Lethaea. 2001g;81:339-341.

    Not in our library

  637. 637.

    Mayr G. Osteological evidence for paraphyly of the avian order Caprimulgiformes (nightjars and allies). Journal of Ornithology. 2002a;143:82-97.

    Not in our library

  638. 638.

    Mayr G. Comments on the osteology of Masillapodargus longipes Mayr 1999 and Paraprefica major Mayr 1999, caprimulgiform birds form the middle Eocene of Messel (Hessen, Germany). Neues Jahrbuch für Geologie und Paläontologie, Monatshefte (Stuttgart). 2002b;2001:65-76.

    Not in our library

  639. 639.

    Mayr G. On the osteology and phylogenetic affinities of the Pseudasturidae – lower Eocene stem-group representatives of parrots (Aves, Psittaciformes). Zoological Journal of the Linnean Society. 2002c;136:715-729.

    Not in our library

  640. 640.

    Mayr G. A skull of a new pelecaniform bird from the middle Eocene of Messel, Germany. Acta Palaeontologica Polonica. 2002d;47:507-512.

    Not in our library

  641. 641.

    Mayr G. The phylogenetic affinities of the shoebill (Balaeniceps rex). Journal für Ornithologie. 2003a;144:157-175.

    Not in our library

  642. 642.

    Mayr G. On the phylogenetic relationships of trogons (Aves, Trogoniformes). Journal of Avian Biology. 2003b;34:81-88.

    Not in our library

  643. 643.

    Mayr G. Phylogeny of early Tertiary swifts and hummingbirds (Aves: Apodiformes). Auk. 2003c;120:145-151.

    Not in our library

  644. 644.

    Mayr G. A partial skeleton of a new fossil loon (Aves, Gaviiformes) from the early Oligocene of Germany with preserved stomach content. Journal of Ornithology. 2004a;145:281-286.

    Not in our library

  645. 645.

    Mayr G. Tertiary plotopterids (Aves, Plotopteridae) and a novel hypothesis on the phylogenetic relationships of penguins (Spheniscidae). Journal of Zoological Systematics and Evolutionary Research. 2004b;10:1-11.

    Not in our library

  646. 646.

    Mayr G. Morphological evidence for sister group relationship between flamingos (Aves: Phoenicopteridae) and grebes (Podicipedidae). Zoological Journal of the Linnean Society. 2004c;140:157-169.

    Not in our library

  647. 647.

    Mayr G. Old World fossil record of modern-type hummingbirds. Science. 2004d;304:861-864.

    Not in our library10.1126/science.1096856

  648. 648.

    Mayr G. The phylogenetic relationships of the early Tertiary Primoscenidae and Sylphornithidae and the sister taxon of crown group piciform birds. Journal of Ornithology. 2004e;15:188-198.

    Not in our library

  649. 649.

    Mayr G. Phylogenetic relationships of the early Tertiary Messel rails (Aves Messelornithidae). Senckenbergiana Lethaea. 2004f;88:317-322.

    Not in our library

  650. 650.

    Mayr G. The Paleogene fossil record of birds in Europe. Biological Reviews (Cambridge). 2005a;80:515-542.

    Not in our library10.1017/s1464793105006779

  651. 651.

    Mayr G. The postcranial osteology and phylogenetic position of the middle Eocene Messelastur gratulator Peters, 1994 – a morphological link between owls (Strigiformes) and ‘falconiform’ birds? Journal of Vertebrate Paleontology. 2005b;25:635-645.

    Not in our library

  652. 652.

    Mayr G. A chicken-sized crane precursor from the early Oligocene of France. Naturwissenschaften. 2005c;92:389-393.

    Not in our library10.1007/s00114-005-0007-8

  653. 653.

    Mayr G. A new Eocene Chascacocolius-like mousebird (Aves: Coliiformes) with a remarkable gaping adaptation. Organisms, Diversity and Evolution. 2005d;5:167-171.

    Not in our library

  654. 654.

    Mayr G. New trogons from the early Tertiary of Germany. Ibis. 2005e;147:512-518.

    Not in our library

  655. 655.

    Mayr G. The Paleogene Old World potoo Paraprefica Mayr, 1999 (Aves, Nyctibiidae): its osteology and affinities to the New World Preficinae Olson, 1987. Journal of Systematic Palaeontology. 2005f;3:359-370.

    Not in our library

  656. 656.

    Mayr G. A, new cypselomorph bird from the middle Eocene of Germany and the early diversification of avian aerial insectivores. Condor. 2005g;107:342-352.

    Not in our library

  657. 657.

    Mayr G. A, tiny barbet-Iike bird from the lower Oligocene of Germany: the smallest species and earliest substantial fossil record of the Pici (woodpeckers and allies). Auk. 2005h;122:1055-1063.

    Not in our library

  658. 658.

    Mayr G. Phylogenetic affinities and composition of the early Eocene Gracilitarsidae (Aves, ?Piciformes). Neues Jahrbuch für Geologie und Paläontologie Monatshefte. 2005i;2005:1-16.

    Not in our library

  659. 659.

    Mayr G. New specimens of the early Eocene stem group galliform Paraortygoides (Gallinuloididae), with comments on the evolution of a crop in the stem lineage of Galliformes. Journal of Ornithology. 2006a;147:31-37.

    Not in our library

  660. 660.

    Mayr G. The renaissance of avian paleontology and its bearing on the higher-level phylogeny of birds: Are there missing links between modern higher-level taxa [abstract]? Journal of Ornithology. 2006b;147(Suppl.):42.

    Not in our library

  661. 661.

    Mayr E, Amadon D. A classification of Recent birds. American Museum Novitates. 1951;1496:1-42.

    Not in our library

  662. 662.

    Mayr G, Clarke J. The deep divergences of neornithine birds: a phylogenetic analysis of morphological characters. Cladistics. 2003;19:527-553.

    Not in our library10.1111/j.1096-0031.2003.tb00387.x

  663. 663.

    Mayr G, Daniels M. Eocene parrots from Messel (Hessen, Germany) and the London Clay of Walton-on-the-Naze (Essex, England). Senckenbergiana Lethaea. 1998;78:157-177.

    Not in our library

  664. 664.

    Mayr G, Daniels M. A new short-legged landbird from the early Eocene of Wyoming and contemporaneous European sites. Acta Palaeontologica Polonica. 2001;46:393-402.

    Not in our library

  665. 665.

    Mayr G, Ericson PGP. Evidence for a sister group relationship between the Madagascan mesites (Mesitornithidae) and the cuckoos (Cuculidae). Senckenbergiana Biologica. 2004;84:1-17.

    Not in our library

  666. 666.

    Mayr G, Göhlich UB. A new parrot from the Miocene of Germany, with comments on the variation of hypotarsus morphology in some Psittaciformes. Belgian Journal of Zoology. 2004;134:47-54.

    Not in our library

  667. 667.

    Mayr G, Manegold A. The oldest European fossil songbird from the early Oligocene of Germany. Naturwissenshaften. 2004;91:173-177.

    Not in our library10.1007/s00114-004-0509-9

  668. 668.

    Mayr G, Manegold A, Johansson US. Monophyletic groups within ‘higher land birds’– comparison of morphological and molecular data. Journal of Zoological Systematics and Evolutionary Research. 2003;41:233-248.

    Not in our library

  669. 669.

    Mayr G, Manegold A, Johansson US. Erratum – monophyletic groups within ‘higher land birds’– comparison of morphological and molecular data. Journal of Zoological Systematics and Evolutionary Research. 2004a;42:173-174.

    Not in our library

  670. 670.

    Mayr G, Mourer-Chauviré C. Rollers (Aves: Coraciiformes s. s.) from the middle Eocene of Messel (Germany) and upper Eocene of the Quercy (France). Journal of Vertebrate Paleontology. 2000;20:533-546.

    Not in our library

  671. 671.

    Mayr G, Mourer-Chauviré C, et al. Auk. 2003;120:202-203.

    Not in our library

  672. 672.

    Mayr G, Mourer-Chauviré C. Unusual tarsometatarsus of a mousebird from the Paleogene of France and the relationships of Selmes Peters, 1999. Journal of Vertebrate Paleontology. 2004;24:366-372.

    Not in our library

  673. 673.

    Mayr G, Mourer-Chauviré C, Weidig I. Osteology and systematic position of the Eocene Primobucconidae (Aves, Coraciiformes sensu stricto), with first records from Europe. Journal of Systematic Paleontology. 2004b;2:1-12.

    Not in our library

  674. 674.

    Mayr G, Peters DS. The mousebirds (Aves: Coliiformes) from the middle Eocene of Grube Messel (Hessen, Germany). Senckenbergiana Lethaea. 1998;78:179-197.

    Not in our library

  675. 675.

    Mayr G, Pohl B, Peters DS. A well-preserved Archaeopteryx specimen with theropod features. Science. 2005;310:1483-1486.

    Not in our library10.1126/science.1120331

  676. 676.

    Mayr G, Smith R. A new record of the Prophaethontidae (Aves: Pelecaniformes) from the middle Eocene of Belgium. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique. 2002;72:135-138.

    Not in our library

  677. 677.

    Mayr G, Weidig I. The early Eocene bird Gallinuloides wyomingensis– a stem group representativve of Galliformes. Acta Palaeontologica Polonica. 2004;49:211-217.

    Not in our library

  678. 678.

    McCall RA, Nee AS, Harvey PH. The role of wing length in the evolution of avian flightlessness. Evolutionary Ecology. 1998;12:569-580.

    Not in our library

  679. 679.

    McCracken KG, Harshman J, McClellan DA, Afton AD. Data set incongruence and correlated character evolution: an example of functional convergence in the hind-limbs of stifftail diving ducks. Systematic Biology. 1999;48:683-714.

    Not in our library10.1080/106351599259979

  680. 680.
  681. 681.

    McCracken KG, Sorenson MD. Is homoplasy or lineage sorting the source of incongruent mtDNA and nuclear gene trees in the stiff-tailed ducks (Nomonyx-Oxyura). Systematic Biology. 2005;54:35-54.

    Not in our library10.1080/10635150590910249

  682. 682.

    McDowell S. The bony palate of birds. Part I, the Palaeognathæ. Auk. 1948;65:520-549.

    Not in our library

  683. 683.

    McKinney ML, McNamara KJ, Zachos LG. Heterochronic hierarchies: application and theory in evolution. Historical Biology. 1990;3:269-287.

    Not in our library

  684. 684.

    McKitrick MC. Forelimb myology of loons (Gaviiformes), with comments on the relationship of loons and tubenoses (Procellariiformes). Zoological Journal of the Linnean Society. 1991a;102:115-152.

    Not in our library

  685. 685.

    McKitrick MC. Phylogenetic analysis of avian hindlimb musculature. University of Michigan, Museum of Zoology Miscellaneous Publications. 1991b;179:1-85.

    Not in our library

  686. 686.

    McKitrick MC. Trends in the evolution of hindlimb musculature in aerial-foraging birds. Auk. 1993;110:189-206.

    Not in our library

  687. 687.

    Meekangvan P, Barhorst AA, Burton TD, Chatterjee S, Schovanec L. Nonlinear dynamical model and response of avian cranial kinesis. Journal of Theoretical Biology. 2006;240:32-47.

    Not in our library10.1016/j.jtbi.2005.08.027

  688. 688.

    Meier R. A test and review of the empirical performance of the ontogenetic criterion. Systematic Biology. 1997;46:699-721.

    Not in our library

  689. 689.

    Meier R, Richter S. Suggestions for a more precise usage of proper names of taxa – ambiguities related to the stem lineage concept. Zeitschrift für Zoologische Systematik und Evolutionsforschung. 1992;30:81-88.

    Not in our library

  690. 690.

    Meyer A, Zardoya R. Recent advances in the (molecular) phylogeny of vertebrates. Annual Review of Ecology and Systematics. 2003;34:311-338.

    Not in our library

  691. 691.

    Middleton KM, Gatesy SM. Theropod forelimb design and evolution. Zoological Journal of the Linnean Society. 2000;128:149-187.

    Not in our library

  692. 692.

    Miller AH. The syringeal structure of the Asiatic owl Phodilus. Condor. 1965;67:536-538.

    Not in our library

  693. 693.

    Milne-Edwards A. Observations sur les affinites zoologiques du genre Phodilus et description d’un nouveau genre de rapace. Nouveau Archives du Musée d’Histoire Naturelle (Série 2). 1878a;1:185-199.

    Not in our library

  694. 694.

    Milne-Edwards A. Remarques sur le genre Mesites et sure la place qu’il doit occuper dans la série ornithologique. Annales des Sciences Naturelles (Série 6, Zoologie). 1878b;7:1-13.

    Not in our library

  695. 695.

    Mindell DP. Phylogeny and classification of birds: a study in molecular evolution [review]. Systematic Biology. 1992;41:126-134.

    Not in our library

  696. 696.

    Mindell DP, Knight A, Baer C, Huddleston CJ. Slow rates of molecular evolution in birds and the metabolic rate and body temperature hypotheses. Molecular Biology and Evolution. 1996;13:422-426.

    Not in our library

  697. 697.

    Mindell DP, Sorenson MD, Dimcheff DE. Multiple independent origins of mitochondrial gene order in birds. Proceedings of the National Academy of Science USA. 1998;95:10693-10697.

    Not in our library10.1073/pnas.95.18.10693

  698. 698.

    Mindell DP, Sorenson MD, Dimcheff DE, Hasegawa M, Ast JC, Yuri T. Interordinal relationships of birds and other reptiles based on whole mitochondrial genomes. Systematic Biology. 1999;48:138-152.

    Not in our library10.1080/106351599260490

  699. 699.

    Mindell DP, Sorenson MD, Huddleston CJ, Miranda HC, Knight A, Swachuk SJ, Yuri T, Mindell DP. Phylogenetic relationships among and within select avian orders based on mitochondrial DNA. Avian molecular evolution and systematics. 1997;213-247.

    Not in our library

  700. 700.

    Minelli A. Molecules, developmental modules, and phenotypes: a combinatorial approach to homology. Molecular Phylogeny and Evolution. 1998;9:340-347.

    Not in our library10.1006/mpev.1997.0490

  701. 701.

    Mishler BD. Cladistic analysis of molecular and morphological data. American Journal of Physical Anthropology. 1994;94:143-156.

    Not in our library10.1002/ajpa.1330940111

  702. 702.

    Mishler BD, Albert VA. The logic of the data matrix in phylogenetic analysis. Parsimony, phylogeny and genomics. 2005;57-70.

    Not in our library

  703. 703.

    Mitchell PC. A contribution to the anatomy of the hoatzin (Opisthocomus cristatus). Proceedings of the Zoological Society of London. 1896;1896:618-628.

    Not in our library

  704. 704.

    Mitchell PC. Observations on the anatomy of the shoebill (Balæniceps rex) and allied birds. Proceedings of the Zoological Society of London. 1913;1913:644-703.

    Not in our library

  705. 705.

    Mitchell PC. Anatomical notes on the gruiform birds Aramus giganteus Bonap. & Rhinochetos kagu. Proceedings of the Zoological Society of London. 1915;1915:413-423.

    Not in our library

  706. 706.

    Mitsiadis TA, Caton J, Cobourne M. Waking-up the Sleeping Beauty: recovery of the ancestral bird ontogeneic program. Journal of Experimental Zoology (Series B). 2006;306:1-7.

    Not in our library10.1002/jez.b.21094

  707. 707.

    Miyaki CY, Matioli SR, Burke T, Wajntal A. Parrot evolution and paleographical events: mitochondrial DNA evidence. Molecular Biology and Evolution. 1998;15:544-551.

    Not in our library

  708. 708.

    Monroe BL. Response to E. Mayr [review]. Auk. 1989;106:515-516.

    Not in our library

  709. 709.

    Mooers AØ, Cotgreave P. Sibley and Ahlquist’s tapestry dusted off. Trends in Ecology and Evolution. 1994;9:458-459.

    Not in our library

  710. 710.

    Mooers AØ, Harvey PH. Metabolic rate, generation time, and the rate of molecular evolution in birds. Molecular Phylogenetics and Evolution. 1994;3:344-350.

    Not in our library10.1006/mpev.1994.1040

  711. 711.

    Moore WS. Inferring phylogenies from mtDNA variation: mitochondrial gene trees versus nuclear gene trees. Evolution. 1995;49:718-726.

    Not in our library10.1111/j.1558-5646.1995.tb02308.x

  712. 712.

    Moore WS, deFilippis VR, Mindell DP. The window of taxonomic resolution for phylogenies based on mitochondrial cytochrome b. Avian molecular evolution and systematics. 1997;83-119.

    Not in our library

  713. 713.

    Mort M, Soltis PS, Soltis DE, Mabry ML. Comparison of three methods for estimating internal support on phylogenetic trees. Systematic Biology. 2000;49:160-171.

    Not in our library10.1080/10635150050207456

  714. 714.

    Moum T, Arnason U, Arnason E. Mitochondrial DNA sequence evolution and phylogeny of the Atlantic Alcidae, including the extinct great auk (Pinguinus impennis). Molecular Biology and Evolution. 2002;19:1434-1439.

    Not in our library10.1093/oxfordjournals.molbev.a004206

  715. 715.

    Moum T, Johansen S, Erikstad KE, Piatt JF. Phylogeny and evolution of the auks (subfamily Alcinae) based on mitochondial DNA sequences. Proceedings of the National Academy of Sciences USA. 1994;91:7912-7916.

    Not in our library10.1073/pnas.91.17.7912

  716. 716.

    Mourer-Chauviré C. The Archaeotrogonidae of the Eocene and Oligocene Phosphorites du Quercy (France). Contributions to Science of the Natural History Museum of Los Angeles County. 1980;330:17-31.

    Not in our library

  717. 717.

    Mourer-Chauviré C. Les Todidae (Aves, Coraciiformes) des Phosphorites du Quercy (France). Verhandlungen der Koninklijke Nederlandse Akademie Van Wetenschappen (Série B). 1985;88:407-414.

    Not in our library

  718. 718.

    Mourer-Chauviré C. Une nouvelle famille de perroquets (Aves: Psittaciformes dans l’Éocène Supérieur des phosphorites du Quercy, France. Geobios Mémoire Spéciale. 1992;14:169-177.

    Not in our library

  719. 719.

    Mourer-Chauviré C. A new species of Ameripodius (Aves: Galliformes: Quercymegapodiidae) from the lower Miocene of France. Palaeontology. 2000;43:481-493.

    Not in our library

  720. 720.

    Mourer-Chauviré C, Balouet JC, Alcover JA, Bover P. Description of the skull of the genus Sylviornis Polin, 1980 (Galliformes, Sylviornithidae new family), a giant extinct bird from the Holocene of New Caledonia. Insular vertebrate evolution: the paleontological approach. Monografies de la Societat d’Història Natural de les Balears. 2005;12:205-118.

    Not in our library

  721. 721.

    Mourer-Chauviré C, Bertjet D, Hugueney M. The late Oligocene birds of the Créchy quarry (Allier, France), with a description of two new genera (Aves: Pelecaniformes: Phalacrocoracidae, and Anseriformes: Anseranatidae). Senckenbergiana Lethaea. 2004;84:303-315.

    Not in our library

  722. 722.

    Moyle RG. Phylogenetics of barbets (Aves: Piciformes) based on nuclear and mitochondrial DNA sequence data. Molecular Phylogenetics and Evolution. 2004;30:187-200.

    Not in our library10.1016/s1055-7903(03)00179-9

  723. 723.

    Moyle RG. Phylogeny and biogeographical history of Trogoniformes, a pantropical bird order. Biological Journal of the Linnean Society. 2005;84:725-738.

    Not in our library

  724. 724.

    Moyle RG. A molecular phylogeny of kingfishers (Alcedinidae) with insights into early biogeographic history. Auk. 2006;123:487-499.

    Not in our library

  725. 725.

    Müller HJ. Die Morphologie und Entwicklung des Craniums von Rhea americana Linné. I. Das knorpelige Neurocranium. Zeitschrift für Wissenschaftliche Zoologie. 1961a;165:221-319.

    Not in our library

  726. 726.

    Müller HJ. Über strukturelle Ähnlichkeiten der Ohr- und Occipitalregion bei Vogel und Säuger. Zoologischer Anzeiger. 1961b;166:391-402.

    Not in our library

  727. 727.

    Müller HJ. Die Morphologie und Entwicklung des Craniums von Rhea americana Linné. II. Viszeralskelett, Mittelohr und Osteocranium. Zeitschrift für Wissenschaftliche Zoologie. 1963;168:35-118.

    Not in our library

  728. 728.

    Müller K. PRAP – computation of Bremer support for large data sets. Molecular Phylogenetics and Evolution. 2004;31:780-782.

    Not in our library10.1016/j.ympev.2003.12.006

  729. 729.

    Müller K. The efficiency of different search strategies for estimating parsimony jackknife, bootstrap, and Bremer support. BMC (Biomed Central) Evolutionary Biology. 2005;5(57):1-10.

    Not in our library10.1186/1471-2148-5-58

  730. 730.

    Müller GB, Newman SA, Bock GR, Cardew G. Generation, integration, autonomy. Three steps in the evolution of homology. Homology. 1999;65-79.

    Not in our library10.1002/9780470515655.ch5

  731. 731.

    Murie J. On the dermal and visceral structures of the kagu, sun-bittern, and boatbill. Transactions of the Zoological Society of London. 1871;7:465-492.

    Not in our library

  732. 732.

    Murie J. On the genus Colius, its structure and systematic position. Ibis. 1872a;14:262-280.

    Not in our library

  733. 733.

    Murie J. On the motmots and their affinities. Ibis. 1872b;14:383-412.

    Not in our library

  734. 734.

    Murie J. On the skeleton of Todus, with remarks as to its allies. Proceedings of the Zoological Society of London. 1872c;1872:664-680.

    Not in our library

  735. 735.

    Murie J. On the Upupidæ and their relationships. Ibis. 1873;15:181-211.

    Not in our library

  736. 736.

    Murray PR, Megirian D. The skull of dromornithid birds: anatomical evidence for their relationship to Anseriformes. Records of the South Australian Museum. 1998;31:51-97.

    Not in our library

  737. 737.

    Murray PR, Vickers-Rich P. Magnificent Mihirungs: the colossal flightless birds of the Australian dreamtime. 2004.

    Not in our library

  738. 738.

    Neff NA. A rational basis for a priori character weighting. Systematic Zoology. 1986;35:110-123.

    Not in our library

  739. 739.

    Nelson G, Hall BK. Homology and systematics. Homology: the hierarchical basis of comparative biology. 1994;101-149.

    Not in our library

  740. 740.

    Nielsen C. Animal evolution: interrelationships of the living phyla. 1995.

    Not in our library

  741. 741.

    Nielsen KK, Arctander P. Recombination among multiple mitochondrial pseudogenes from a passerine genus. Molecular Phylogenetics and Evolution. 2001;18:362-369.

    Not in our library10.1006/mpev.2000.0885

  742. 742.

    Nixon KC. The parsimony ratchet, a new method for rapid parsimony analysis. Cladistics. 1999;15:407-414.

    Not in our library10.1111/j.1096-0031.1999.tb00277.x

  743. 743.

    Norell MA, Novacek MJ, Wheeler QD. Taxic origin and temporal diversity: the effect of phylogeny. Extinction and phylogeny. 1992;89-118.

    Not in our library

  744. 744.

    Norell MA, Clark JN, Dasheveg D, Barsbold R, Chiappe LM, Davidson AR, McKenna MC, Perle A, Novacek MJ. A theropod dinosaur embryo and the affinities of the Flaming Cliffs dinosaur eggs. Science. 1994;266:779-782.

    Not in our library10.1126/science.266.5186.779

  745. 745.

    Norell MA, Clarke JA. Fossil that fills a critical gap in avian evolution. Nature. 2001;409:181-184.

    Not in our library10.1038/35051563

  746. 746.

    Norell MA, Wheeler W. Missing entry replacement data analysis: a replacement approach to dealing with missing data in paleontological and total evidence data sets. Journal of Vertebrate Paleontology. 2003;23:275-283.

    Not in our library

  747. 747.

    Noriega JI, Tambussi CO. A late Cretaceous Presbyornithidae (Aves: Anseriformes) from Vega Island, Antarctic peninsula: paleobiogeographic implications. Ameghiniana. 1995;32:57-61.

    Not in our library

  748. 748.

    Nudds RL, Rayner JMV. Scaling of body frontal area and body width in birds. Journal of Morphology. 2006;267:341-346.

    Not in our library10.1002/jmor.10409

  749. 749.

    Nunn GB, Cooper J, Jouventin P, Robertson CJR, Robertson GG. Evolutionary relationships among extant albatrosses (Procellariiformes: Diomedeidae) established from complete cytochrome-b gene sequences. Auk. 1996;113:784-801.

    Not in our library

  750. 750.

    Nunn GB, Cracraft J. Phylogenetic relationships among major lineages of the birds-of-paradise (Paradisaeidae) using mitochondrial DNA gene sequences. Molecular Phylogenetics and Evolution. 1996;5:445-459.

    Not in our library10.1006/mpev.1996.0041

  751. 751.

    Nunn GB, Stanley SE. Body size effects and rates of cytochrome b evolution in tube-nosed seabirds. Molecular Biology and Evolution. 1998;15:1360-1371.

    Not in our library10.1093/oxfordjournals.molbev.a025864

  752. 752.

    Ödeen A, Håstad O. Complex distribution of avian color vision systems revealed by sequencing the SWS1 opsin from total DNA. Molecular Biology and Evolution. 2003;20:855-861.

    Not in our library10.1093/molbev/msg108

  753. 753.

    Ogilvie-Grant WR. On the genus Turnix. Ibis. 1889;31:446-475.

    Not in our library

  754. 754.

    Oliveira CA, Silva RM, Santos MM, Mahecha GAB. Location of the uretal openings in the cloacas of tinamous, some ratite birds, and crocodilians: a primitive character. Journal of Morphology. 2004;260:234-246.

    Not in our library10.1002/jmor.10217

  755. 755.

    Olson SL. Taxonomic comments on the Eurylaimidae. Ibis. 1971;113:507-516.

    Not in our library

  756. 756.

    Olson SL. Oligocene fossils bearing on the origins of the Todidae and the Momotidae (Aves: Coraciiformes). Smithsonian Contributions to Paleobiology. 1976;27:111-119.

    Not in our library

  757. 757.

    Olson SL. A lower Eocene frigatebird from the Green River Formation of Wyoming (Pelecaniformes, Fregatidae). Smithsonian Contributions to Paleobiology. 1977;35:1-33.

    Not in our library

  758. 758.

    Olson SL. Multiple origins of the Ciconiiformes. Proceedings of Conference of the Colonial Waterbird Group. 1978;1978:165-170.

    Not in our library

  759. 759.

    Olson SL. A new genus of penguin-like pelecaniform bird from the Oligocene of Washington (Pelecaniformes: Plotopteridae). Natural History Museum of Los Angeles County Contributions in Science. 1980;330:51-57.

    Not in our library

  760. 760.

    Olson SL. A critique of Cracraft’s classification of birds. Auk. 1982;99:737-759.

    Not in our library

  761. 761.

    Olson SL. Evidence for a polyphyletic origin of the Piciformes. Auk. 1983a;100:126-133.

    Not in our library

  762. 762.

    Olson SL. A new genus of tropicbird (Pelecaniformes: Phaethontidae) from the middle Miocene Calvert Formation of Maryland. Proceedings of the Biological Society of Washington. 1983b;98:851-855.

    Not in our library

  763. 763.

    Olson SL, Farner DS, King JR, Parkes KC. The fossil record of birds. Avian biology. 1985;8:79-238.

    Not in our library

  764. 764.

    Olson SL. An early Eocene oilbird from the Green River Formation of Wyoming (Caprimulgiformes: Steatornithidae). Documents des Laboratoires de Géologie de Lyon. 1987;99:57-99.

    Not in our library

  765. 765.

    Olson SL. Neogaeornis wetzeli Lambrecht, a Cretaceous loon from Chile (Aves: Gaviidae). Journal of Vertebrate Paleontology. 1992a;12:122-124.

    Not in our library

  766. 766.

    Olson SL. A new family of primitive landbirds from the lower Eocene Green River Formation of Wyoming. Natural History Museum of Los Angeles County, Science Series. 1992b;36:127-136.

    Not in our library

  767. 767.

    Olson SL. A giant Presbyornis (Aves: Anseriformes) from the Palaeocene Aquia Formation of Maryland. Proceedings of the Biological Society of Washington. 1994;107:429-435.

    Not in our library

  768. 768.

    Olson SL. A new species of pelican (Aves: Pelecanidae) from the lower Pliocene of North Carolina and Florida. Proceedings of the Biological Society of Washington. 1999a;112:503-509.

    Not in our library

  769. 769.

    Olson SL. The anseriform relationships of Anatalavis Olson and Parris (Anseranatidae), with a new species of the London Clay. Smithsonian Contributions to Paleobiology. 1999b;89:231-243.

    Not in our library

  770. 770.

    Olson SL. Why so many kinds of passerine birds? Bioscience. 2001;51:268-269.

    Not in our library

  771. 771.

    Olson SL, Feduccia A. Presbyornis and the origin of the Anseriformes (Aves: Charadriomorphae). Smithsonian Contributions to Zoology. 1980a;323:1-24.

    Not in our library

  772. 772.

    Olson SL, Feduccia A. Relationships and evolution of flamingos (Aves: Phoenicopteridae). Smithsonian Contributions to Zoology. 1980b;316:1-73.

    Not in our library

  773. 773.

    Olson SL, Hasegawa Y. Fossil counterparts of giant penguins from the North Pacific. Science. 1979;206:688-689.

    Not in our library10.1126/science.206.4419.688

  774. 774.

    Olson SL, Hasegawa Y. A new genus and two new species of gigantic Plotopteridae from Japan (Aves: Pelecaniformes). Journal of Vertebrate Paleontology. 1996;16:742-751.

    Not in our library

  775. 775.

    Olson SL, Houde P, Ouellet H. Small arboreal nonpasserine birds from the Early Tertiary of western North America. Acta XIX Congressua Internationalia Ornithologici. 1989;2030-2036.

    Not in our library

  776. 776.

    Olson SL, Matsuoka H. New specimens of the early Eocene frigatebirds Limnofregata (Pelecaniformes: Fregatidae), with the description of a new species. Zootaxa. 2005;1046:1-15.

    Not in our library

  777. 777.

    Olson SL, Parris DC. The Cretaceous birds of New Jersey. Smithsonian Contributions to Paleobiology. 1987;63:1-22.

    Not in our library

  778. 778.

    Olson SL, Rasmussen PC. Miocene and Pliocene birds from the Lee Creek Mine, North Carolina. Smithsonian Contributions to Paleobiology. 2001;90:233-365.

    Not in our library

  779. 779.

    Olson SL, Steadman DW. The relationships of the Pedionomidae (Aves: Charadriiformes). Smithsonian Contributions to Zoology. 1981;337:1-25.

    Not in our library

  780. 780.

    Omland KE. Correlated rates of molecular and morphological evolution. Evolution. 1997a;51:1381-1393.

    Not in our library10.1111/j.1558-5646.1997.tb01461.x

  781. 781.

    Omland KE. Examining two standard assumptions of ancestral reconstructions: repeated loss of dichromatism in dabbling ducks (Anatini). Evolution. 1997b;51:1636-1646.

    Not in our library10.1111/j.1558-5646.1997.tb01486.x

  782. 782.

    Ovenden JR, Mackinlay AG, Crozier RH. Systematics and mitochondrial genome evolution of Australian rosellas (Aves: Platycercidae). Molecular Biology and Evolution. 1987;4:526-543.

    Not in our library

  783. 783.

    Overton LC, Rhoads DD. Molecular phylogenetic relationships based on mitochondrial and nuclear gene sequences for the todies (Todus, Todidae) of the Caribbean. Molecular Phylogenetics and Evolution. 2004;32:524-538.

    Not in our library10.1016/j.ympev.2004.01.004

  784. 784.

    Owen R. Description of the skull of a dentigerous bird (Odontopteryx toliapicus, Ow.) from the London Clay of Sheppey. Quarterly Journal of the Geological Society of London. 1873;29:511-522.

    Not in our library

  785. 785.

    Padian K, Chiappe LM. The origin and early evolution of birds. Biological Reviews (Cambridge). 1998;73:1-42.

    Not in our library

  786. 786.

    Page RDM. On islands of trees and efficacy of different methods of branch swapping in finding most-parsimonious trees. Systematic Biology. 1993;42:200-209.

    Not in our library

  787. 787.

    Page RDM, Charleston M. From gene to organismal phylogeny: reconciled trees and the gene tree/species tree problem. Molecular Phylogenetics and Evolution. 1997;7:231-240.

    Not in our library10.1006/mpev.1996.0390

  788. 788.

    Page RDM, Lee PLM, Becher SA, Griffiths R, Clayton DH. A different tempo of mitochondrial DNA evolution in birds and their parasitic lice. Molecular Phylogenetics and Evolution. 1998;9:276-293.

    Not in our library10.1006/mpev.1997.0458

  789. 789.

    Pamilo P, Nei M. Relationships between gene trees and species trees. Molecular Biology and Evolution. 1988;5:568-583.

    Not in our library10.1093/oxfordjournals.molbev.a040517

  790. 790.

    Parker WK. Abstract of notes on the osteology of Balæniceps rex. Proceedings of the Zoological Society of London. 1860;1860:324-330.

    Not in our library

  791. 791.

    Parker WK. On the osteology of Balæniceps rex (Gould). Transactions of the Zoological Society of London. 1861;4:269-351.

    Not in our library

  792. 792.

    Parker WK. Abstract of a memoir on the osteology of the genera Pterocles, Syrrhaptes, Hemopodius, and Tinamus. Proceedings of the Zoological Society of London. 1862;1862:253-260.

    Not in our library

  793. 793.

    Parker WK. On the osteology of the kagu (Rhinochetus jubatus). Transactions of the Zoological Society of London. 1869;8:501-521.

    Not in our library

  794. 794.

    Parker WK. On the ‘manus’ of Phœnicopterus. Ibis. 1889a;31:183-185.

    Not in our library

  795. 795.

    Parker WK. On the osteology of Steatornis caripensis. Proceedings of the Zoological Society of London. 1889b;1889:161-190.

    Not in our library

  796. 796.

    Parker WK. On the morphology of a reptilian bird, Opisthocomus cristatus. Transactions of the Zoological Society of London. 1891;13:43-85.

    Not in our library

  797. 797.

    Parsons CW. Note on the embryonic development of the hoatzin (Opisthocomus hoazin). Proceedings of the Royal Society of Edinburgh (Series B). 1954;65:205-212.

    Not in our library

  798. 798.

    Patak AE, Baldwin J. Pelvic limb musculature in the emu Dromaius novaehollandiae (Aves: Struthioniformes: Dromaiidae): adaptations to high-speed running. Journal of Morphology. 1998;238:23-37.

    Not in our library10.1002/(sici)1097-4687(199810)238:1<23::aid-jmor2>3.0.co;2-o

  799. 799.

    Paterson AM, Gray RD, Clayton DH, Moore J. Analytical tests of host/parasite cospeciation. Coevolutionary biology of birds and parasites. 1996;236-259.

    Not in our library

  800. 800.

    Paterson AM, Gray RD, Wallis GP. Parasites, petrels and penguins: Does louse presence reflect seabird phylogeny? International Journal of Parasitology. 1993;23:515-526.

    Not in our library

  801. 801.

    Paterson AM, Wallis GP, Gray RD. Penguins, petrels, and parsimony: Does cladistic analysis of behavior reflect seabird phylogeny? Evolution. 1995;49:974-989.

    Not in our library10.1111/j.1558-5646.1995.tb02332.x

  802. 802.

    Paton TA, Baker AJ. Sequences from 14 mitochondrial genes provide a well-supported phylogeny of the charadriiform birds congruent with the nuclear RAG-1 tree. Molecular Phylogenetics and Evolution. 2006;39:657-667.

    Not in our library10.1016/j.ympev.2006.01.011

  803. 803.

    Paton TA, Baker AJ, Groth JG, Barrowclough GF. RAG−1 sequences resolve phylogenetic relationships within charadriiform birds. Molecular Phylogenetics and Evolution. 2003;29:268-278.

    Not in our library10.1016/s1055-7903(03)00098-8

  804. 804.

    Paton TA, Haddrath O, Baker AJ. Complete mitochondrial DNA genome sequences show that modern birds are not descended from transitional shorebirds. Proceedings of the Royal Society of London (Series B). 2002;269:839-846.

    Not in our library10.1098/rspb.2002.1961

  805. 805.

    Patterson C, Williams DM, Humphries CJ. Congruence between molecular and morphological phylogenies. Annual Review of Ecology and Systematics. 1993;24:153-188.

    Not in our library

  806. 806.

    Paxinos EE, James HF, Olson SL, Sorenson MD, Jackson J, Fleischer RC. mtDNA from fossils reveals of radiation of Hawaiian geese recently derived from the Canada goose (Branta canadensis). Proceedings of the National Academy of Science USA. 2002;99:1399-1404.

    Not in our library10.1073/pnas.032166399

  807. 807.

    Pereira SL, Baker AJ. Vicariant speciation of curassows (Aves, Cracidae): a hypothesis based on mitochondrial DNA phylogeny. Auk. 2004;121:682-694.

    Not in our library

  808. 808.

    Pereira SL, Baker AJ. Multiple gene evidence for parallel evolution and retention of ancestral morphological states in the shanks (Charadriiformes: Scolopacidae). Condor. 2005;107:514-526.

    Not in our library

  809. 809.

    Pereira SL, Baker AJ. A molecular timescale for galliform birds accounting for uncertainty in time estimate and heterogeneity of rates of DNA substitutions across lineages and sites. Molecular Phylogenetics and Evolution. 2006a;38:499-509.

    Not in our library10.1016/j.ympev.2005.07.007

  810. 810.

    Pereira SL, Baker AJ. A mitogenomic timescale for birds detects variable phylogenetic rates of molecular evolution and refutes the standard molecular clock. Molecular Biology and Evolution. 2006b;23:1731-1740.

    Not in our library10.1093/molbev/msl038

  811. 811.

    Pereira SL, Baker AJ, Wajntal A. Combined nuclear and mitochondrial DNA sequences resolve generic relationships within the Cracidae (Galliformes, Aves). Systematic Biology. 2002;51:94-958.

    Not in our library10.1080/10635150290102519

  812. 812.

    Perrin JB. On the myology of Opisthocomus cristatus. Transactions of the Zoological Society of London. 1875;9:353-370.

    Not in our library

  813. 813.

    Peters JL. Check-list of birds of the world. 1934;II.

    Not in our library

  814. 814.

    Philippe H, Laurent J. How good are deep phylogenetic trees? Current Opinions on Genetic Development. 1998;8:616-623.

    Not in our library10.1016/s0959-437x(98)80028-2

  815. 815.

    Philippe H, Lecointre G, Vân Lê HL, Guyader JL. A critical study of homoplasy in molecular data with the use of a morphologically based cladogram, and its consequences for character weighting. Molecular Biology and Evolution. 1996;13:1174-1186.

    Not in our library

  816. 816.
  817. 817.

    Phillips A, Janies D, Wheeler W. Multiple sequence alignment in phylogenetic analysis. Molecular Phylogenetics and Evolution. 2000;16:317-330.

    Not in our library10.1006/mpev.2000.0785

  818. 818.

    Pickett KM, Randle CP. Strange Bayes indeed: uniform topological priors imply non-uniform clade priors. Molecular Phylogenetics and Evolution. 2005;34:203-211.

    Not in our library10.1016/j.ympev.2004.09.001

  819. 819.

    Pickett KM, Tolman GL, Wheeler WC, Wenzel JW. Parsimony overcomes statistical inconsistency with the addition of more data from the same gene. Cladistics. 2005;21:438-445.

    Not in our library10.1111/j.1096-0031.2005.00076.x

  820. 820.

    Pisani D, Yates AM, Langer MC, Benton MJ. A genus-level supertree of the Dinosauria. Proceedings of the Royal Society of London (Series B). 2002;269:915-921.

    Not in our library10.1098/rspb.2001.1942

  821. 821.

    Pitra C, Lieckfeldt D, Frahnert S, Fickel J. Phylogenetic relationships and ancestral areas of the bustards (Gruiformes: Otididae), inferred from mitochondrial DNA and nuclear intron sequences. Molecular Phylogenetics and Evolution. 2002;23:63-74.

    Not in our library10.1006/mpev.2001.1078

  822. 822.

    Ploeger PL. Geographical differentiation in arctic Anatidae as a result of isolation during the last glacial. Ardea. 1968;56:1-159.

    Not in our library

  823. 823.

    Poe S, Chubb AL. Birds in a bush: five genes indicate explosive evolution of avian orders. Evolution. 2004;58:404-415.

    Not in our library

  824. 824.

    Pol D, Norell MA, Siddall ME. Measures of stratigraphic fit to phylogeny and their sensitivity to tree size, tree shape, and scale. Cladistics. 2004;20:64-75.

    Not in our library10.1111/j.1096-0031.2003.00002.x

  825. 825.

    Pollock DD, Zwickl DJ, McGuire JA, Hillis DM. Increased taxon sampling is advantageous for phylogenetic inference. Systematic Biology. 2002;51:664-671.

    Not in our library10.1080/10635150290102357

  826. 826.

    Pons J-M, Hassanin A, Crochet P-A. Phylogenetic relationships within the Laridae (Charadriiformes: Aves) inferred from mitochondrial markers. Molecular Phylogenetics and Evolution. 2005;37:686-699.

    Not in our library10.1016/j.ympev.2005.05.011

  827. 827.

    Poplin F, Mourer-Chauviré C. Sylviornis neocaledoniae (Aves, Galliformes, Megapodidae), oiseau géant éteint de l’Ile des Pins (Nouvelle-Calédonie). Geobios. 1985;18:73-97.

    Not in our library

  828. 828.

    Posso SR, Donatelli RJ. Cranial osteology and systematic implications in Crotophaginae (Aves, Cuculidae). Journal of Zoological Systematics and Evolutionary Research. 2001;39:247-256.

    Not in our library

  829. 829.

    Prager EM, Wilson AC. Slow evolutionary loss of the potential for interspecific hybridization in birds: a manifestation of slow regulatory evolution. Proceedings of the National Academy of Science USA. 1975;72:200-204.

    Not in our library10.1073/pnas.72.1.200

  830. 830.

    Prager EM, Wilson AC. Congruency of phylogenies derived from different proteins: a molecular analysis of the phylogenetic position of cracid birds. Journal of Molecular Evolution. 1976;9:45-57.

    Not in our library10.1007/bf01796122

  831. 831.

    Prager EM, Wilson AC, Osuga DT, Feeney RE. Evolution of flightless land birds on southern continents: transferrin comparison shows monophyletic origin of ratites. Journal of Molecular Evolution. 1976;8:283-294.

    Not in our library10.1007/bf01731001

  832. 832.

    Prendini L. Species or supraspecific taxa as terminals in cladistic analysis? Groundplans versus exemplars revisted. Systematic Biology. 2003;50:290-300.

    Not in our library10.1080/10635150118650

  833. 833.

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    Prum RO. Phylogenetic interrelationships of the barbets (Capitonidae) and toucans (Ramphastidae) based on morphology with comparisons to DNA-DNA hybridization. Zoological Journal of the Linnean Society. 1988;92:313-343.

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    Prum RO. Phylogeny, biogeography, and evolution of the broadbills (Eurylaimidae) and asites (Philepittidae) based on morphology. Auk. 1993;110:304-324.

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    Prychitko TM, Moore WS. The utility of DNA sequences of an intron from the β-fibrinogen gene in phylogenetic analysis of woodpeckers (Aves: Picidae). Molecular Phylogenetics and Evolution. 1997;8:193-204.

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    Prychitko TM, Moore WS. Alignment and phylogenetic analysis of β-fibrinogen intron 7 sequences among avian orders reveal conserved regions within the intron. Molecular Biology and Evolution. 2003;20:762-771.

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  839. 839.

    Quinn TW. The genetic legacy of Mother Goose – phylogeographic patterns of lesser snow goose Chen caerulescens caerulescens maternal lineages. Molecular Ecology. 1992;1:1-5–711.

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    Raff RA, Parr BA, Parks AL, Wray GA, Nitecki MH. Heterochrony and other mechanisms of radical evolutionary change in early development. Evolutionary innovations. 1990;71-98.

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  844. 844.

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  845. 845.

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    Raikow RJ. A phylogeny of the woodcreepers (Dendrocolaptinae). Auk. 1994a;111:104-114.

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    Raikow RJ. Climbing adaptations in the hindlimb musculature of the woodcreepers (Dendrocolaptinae). Condor. 1994b;96:1103-1106.

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    Raikow RJ, Bledsoe AH. Phylogeny and evolution of passerine birds. Bioscience. 2000;50:487-499.

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    Raikow RJ, Borecky SR, Berman SL. The evolutionary reestablishment of a lost ancestral muscle in the bowerbird assemblage. Condor. 1980;81:203-206.

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    Randi E, Fusco G, Lorenzini R, Spina F. Allozyme divergence and phylogenetic-relationships within the Strigiformes. Condor. 1991;93:295-301.

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    Rawal UM, Bhatt PL. Comparative morphology of the feeding apparatus in a few representative birds from order Coraciiformes. Vidya (Series B). 1974;17:1-21.

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    Rea AM, Wilbur SR, Jackson JA. Cathartid affinities: a brief overview. Vulture biology and management. 1983;26-54.

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    Redelings BD, Suchard MA. Joint Bayesian estimation of alignment and phylogeny. Systematic Biology. 2005;54:401-408.

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    Ree RH, Donoghue MJ. Step matrices and the interpretation of homoplasy. Systematic Biology. 1998;47:582-588.

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    Rees J, Lindgren J. Aquatic birds from the upper Cretaceous (lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology. 2005;48:1321-1329.

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    Reinhardt J. On the affinities of Balæniceps. Proceedings of the Zoological Society of London. 1860;1860:377-380.

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    Rice KA, Donoghue MJ, Olmstead RG. Analyzing large data sets: rbcL 500 revisited. Systematic Biology. 1997;46:554-563.

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  864. 864.

    Rich PV. The Dromornithidae, an extinct family of large ground birds endemic to Australia. Bulletin of Bureau of Natural Resources, Geology and Geophysics. 1979;184:1-196.

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    Rich PV. The Australian Dromornithidae: a group of large extinct ratites. Los Angeles County Natural History Museum Contributions to Science. 1980;330:93-103.

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    Rieppel O, Hall BK. Homology, topology, and typology: the history of modern debates. Homology: the hierarchical basis of comparative biology. 1994;63-100.

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    Rotthowe K, Starck JM. Evidence for a phylogenetic position of button quails (Turnicidae: Aves) among the Gruiformes. Journal of Zoological Systematics and Evolutionary Research. 1998;36:39-51.

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    Roulin A. The evolution, maintenance and adaptive function of genetic colour polymorphism in birds. Biological Reviews (Cambridge). 2004;79:815-848.

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    Russello MA, Amato G. A molecular phylogeny of Amazona: implications for Neotropical parrot biogeography, taxonomy, and conservation. Molecular Phylogenetics and Evolution. 2004;30:421-477.

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    Ruta M, Coates MI, Quicke DLJ. Early tetrapod relationships revisited. Biological Reviews (Cambridge). 2003;78:251-345.

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  876. 876.

    Salter LA. Complexity of the likelihood surface for a large DNA dataset. Systematic Biology. 2001;50:970-978.

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    Sanderson MJ. In search of homoplastic tendencies: statistical inference of topological patterns in homoplasy. Evolution. 1991;45:351-358.

    Not in our library10.1111/j.1558-5646.1991.tb04409.x

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    Sanderson MJ. Objections to bootstrapping phylogenies: a critique. Systematic Biology. 1995;44:299-320.

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  879. 879.

    Sanderson MJ. A nonparametric approach to estimating divergence times in the absence of rate constancy. Molecular Biology and Evolution. 1997;14:1218-1231.

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  880. 880.

    Sanderson MJ, Donoghue MJ. Patterns of variation in levels of homoplasy. Evolution. 1989;43:1781-1795.

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    Sanderson MJ, Donoghue MJ, Sanderson MJ, Hufford L. The relationship between homoplasy and confidence in a phylogenetic tree. Homoplasy: the recurrence of similarity in evolution. 1996;67-89.

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  883. 883.

    Santini F, Stellwag EJ. Phylogeny, fossils, and model systems in the study of evolutionary developmental biology. Molecular Phylogenetics and Evolution. 2002;24:379-383.

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  885. 885.

    Saunders DA, Smith GT, Campbell NA. The relationship between body weight, egg weight, incubation period, nestling period and nest site in the Psittaciformes, Falconiformes, Strigiformes, and Columbiformes. Australian Journal of Zoology. 1984;32:57-67.

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  886. 886.

    Scherer S, Hilsberg T. Hybridisierung und Verwandtschaftsgrade innerhalb der Anatidae – eine systematische und evolutionstheoretische Betrachtung. Journal für Ornithologie. 1982;123:357-380.

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    Schluter D. The ecology of adaptive radiation. 2000.

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    Schulmeister S, Wheeler WC. Comparative and phylogenetic analysis of developmental sequences. Evolution and Development. 2004;6:50-57.

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  889. 889.

    Schweitzer MH, Jackson FD, Chiappe LM, Schmitt JG. Late Cretaceous avian eggs with embryos from Argentina. Journal of Vertebrae Paleontology. 2002;22:191-195.

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  890. 890.

    Scotland RW, Olmstead RG, Bennett JR. Phylogeny reconstruction: the role of morphology. Systematic Biology. 2003;52:539-548.

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  891. 891.

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    Seebohm H. An attempt to diagnose the suborders of the ancient Ardeino-Anserine assemblage of birds by the aid of osteological characters alone. Ibis. 1889;31:92-104.

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    Seebohm H. An attempt to diagnose the subclass Coraciiformes and the orders, suborders, and families comprised therein. Ibis. 1890a;32:200-205.

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    Seebohm H. The classification of birds: an attempt to classify the subclasses, orders, suborders, and some of the families of existing birds. 1890b.

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  895. 895.

    Seebohm H. An attempt to diagnose the Pico-Passerine group of birds and the suborders of which it consists. Ibis. 1890c;32:29-37.

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    Seebohm H. Classification of birds: an attempt to classify the subclasses, orders, suborders, and some of the families of existing birds (Supplement). 1895.

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  897. 897.

    Seibel DE. A phylogenetic analysis of the Cuculiformes and Opisthocomus, based on postcranial skeletal characters. 1988.

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  898. 898.

    Seibold I, Helbig AJ. Evolutionary history of New and Old world vultures inferred from nucleotide sequences of the mitochondrial cytochrome b gene. Philosophical Transactions of the Royal Society of London (Series B). 1995;150:163-178.

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  899. 899.

    Seibold I, Helbig AJ. Phylogenetic relationships of the sea eagles (genus Haliaetus): reconstruction based on morphology, allozymes, and mitochondrial DNA sequences. Journal of Zoological Systematics and Evolutionary Research. 1996;34:103-112.

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  900. 900.

    Semple C, Steel M. Phylogenetics. 2003.

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  901. 901.

    Sepkowski JJ, Magurran AE, May RM. Rates of speciation in the fossil record. Evolution of biological diversity. 1999;260-282.

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  902. 902.

    Sereno PC. The pectoral girdle and forelimb of the basal theropod Herrerasaurus ischigualastensis. Journal of Vertebrate Paleontology. 1994;13(1993):425-450.

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  903. 903.

    Sereno PC, Gauthier J, Gall LF. Alvarezsaurids: birds or ornithomimosaurs? New perspectives on the origin and early evolution of birds. 2001;69-98.

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  904. 904.

    Sereno PC, Novas FE. The skull and neck of the basal theropod Herrerasaurus ischigualastensis. Journal of Vertebrate Paleontology. 1994;13(1993):451-476.

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  905. 905.

    Shafer HB, Clark JM, Kraus F. When molecules and morphology clash: a phylogenetic analysis of the North American ambystomatid salamanders (Caudata: Ambystomatidae). Systematic Zoology. 1991;40:284-305.

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  906. 906.

    Shapiro B, Sibthorpe D, Rambaut A, Austin J, Wragg GM, Bininda-Emonds ORP, Lee PLM, Cooper A. Flight of the dodo. Science. 2002;295:1683.

    Not in our library10.1126/science.295.5560.1683

  907. 907.

    Sharkey MJ. A hypothesis-independent method of character weighting for cladistic analysis. Cladistics. 1989;5:63-86.

    Not in our library10.1111/j.1096-0031.1989.tb00483.x

  908. 908.

    Sheehan PM, Fastovsky DE. Major extinctions of land-dwelling vertebrates at the Cretaceous–Tertiary boundary, eastern Montana. Geology. 1992;20:556-570.

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  909. 909.

    Sheldon FH, Jones CE, McCracken KG. Relative patterns and rates of evolution in heron nuclear and mitochondrial DNA. Molecular Biology and Evolution. 2000;17:437-450.

    Not in our library10.1093/oxfordjournals.molbev.a026323

  910. 910.

    Shetty S, Griffin DK, Graves JAM. Comparative painting reveals strong chromosome homology over 80 million years of bird evolution. Chromosome Research. 1999;7:289-295.

    Not in our library10.1023/a:1009278914829

  911. 911.

    Shields GF, Wilson AC. Calibration of mitochondrial DNA evolution in geese. Journal of Molecular Evolution. 1987;24:212-217.

    Not in our library10.1007/bf02111234

  912. 912.

    Shpak M, Churchill GA. The information content of a character under a Markov model of evolution. Molecular Phylogenetics and Evolution. 2000;17:231-243.

    Not in our library10.1006/mpev.2000.0846

  913. 913.

    Shubin NH, Grande L, Rieppel O. The phylogeny of development and the origin of homology. Interpreting the hierarchy of nature: from systematic patterns to evolutionary process theories. 210-225.

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  914. 914.

    Shufeldt RW. Contribution to the comparative osteology of the Trochilidæ, Caprimulgidæ, and Cypselidæ. Proceedings of the Zoological Society of London. 1885;1885:886-915.

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  915. 915.

    Shufeldt RW. Note on the anserine affinities of the flamingoes. Science. 1889a;14:224-225.

    Not in our library10.1126/science.ns-14.347.224-b

  916. 916.

    Shufeldt RW. Studies of the Macrochires, morphological and otherwise, with the view of indicating their relationships and defining their several positions in the system. Journal of the Linnean Society of London. 1889b;20:299-394.

    Not in our library

  917. 917.

    Shufeldt RW. On the osteology of the Striges (Strigidæ and Bubonidæ). Proceedings of the American Philosophical Society. 1900;39:665-722.

    Not in our library

  918. 918.

    Shufeldt RW. Notes on the osteology of Scopus umbretta and Balaeniceps rex. Journal of Anatomy (Series 2). 1901a;15:405-412.

    Not in our library

  919. 919.

    Shufeldt RW. Osteology of the flamingoes (Odontoglossæ). Family: Phoenicopteridæ, sp. P. ruber. Annals of Carnegie Museum. 1901b;1:295-324.

    Not in our library

  920. 920.

    Shufeldt RW. On the systematic position of the sand-grouse (Pterocles; Syrrhaptes). American Naturalist. 1901c;35:11-16.

    Not in our library

  921. 921.

    Shufeldt RW. Notes on the osteology of the young of the hoatzin (Opisthocomus cristatus) and other points on its morphology. Journal of Morphology. 1918;31:599-606.

    Not in our library

  922. 922.

    Sibley CG. The evolutionary and taxonomic significance of sexual dimorphism and hybridization in birds. Condor. 1957;59:166-191.

    Not in our library

  923. 923.

    Sibley CG. The relationships of the lyrebirds. Emu. 1974;74:65-79.

    Not in our library

  924. 924.

    Sibley CG, Ahlquist JE. A comparative study of the egg white proteins of passerine birds. Peabody Museum of Natural History Bulletin. 1970;32:1-131.

    Not in our library

  925. 925.

    Sibley CG, Ahlquist JE. A comparative study of the egg white proteins of non-passerine birds. Peabody Museum of Natural History Bulletin. 1972;39:1-276.

    Not in our library

  926. 926.

    Sibley CG, Ahlquist JE. The relationships of the hoatzin. Auk. 1973;90:1-13.

    Not in our library

  927. 927.

    Sibley CG, Ahlquist JE, Scudder GGE, Reveal JL. The phylogeny and relationships of the ratite birds as indicated by DNA-DNA hybridization. Evolution today. 1981;301-335.

    Not in our library

  928. 928.

    Sibley CG, Ahlquist JE, Paterson C. Avian phylogeny reconstructed from comparisons of the genetic material, DNA. Molecules and morphology in evolution: conflict or compromise? 1987;95-121.

    Not in our library

  929. 929.

    Sibley CG, Ahlquist JE. Phylogeny and classification of birds: a study in molecular evolution. 1990.

    Not in our library

  930. 930.

    Sibley CG, Ahlquist JE, Monroe BL. A classification of the living birds of the world based on DNA–DNA hybridization studies. Auk. 1988;105:409-423.

    Not in our library

  931. 931.

    Sibley CG, Ahlquist JE, Monroe BL. Distribution and taxonomy of birds of the world. 1990.

    Not in our library

  932. 932.

    Sibley CG, Ahlquist JE, DeBenedictus P. The phylogenetic relationships of the rails, based on DNA comnparisons. Journal of the Yamashina Institute of Ornithology. 1993;25:1-11.

    Not in our library

  933. 933.

    Sibley CG, Frelin C. The egg white protein evidence for ratite affinities. Ibis. 1972;114:377-387.

    Not in our library

  934. 934.

    Siegel-Causey D. Phylogeny of the Phalacrocoracidae. Condor. 1988;90:885-905.

    Not in our library

  935. 935.

    Siegel-Causey D, Mindell DP. Phylogeny of the Pelecaniformes: molecular systematics of a privative group. Avian molecular evolution and systematics. 1997;159-171.

    Not in our library

  936. 936.

    Simmons NB. Misleading results from the use of ambiguity coding to score polymorphisms in higher-level taxa. Systematic Biology. 2001;50:613-620.

    Not in our library10.1080/10635150120578

  937. 937.

    Simmons MP, Pickett KM, Miya M. How meaningful are Bayesian support values? Molecular Biology and Evolution. 2004;21:188-199.

    Not in our library10.1093/molbev/msh014

  938. 938.

    Simmons MP, Reeves A, Davis JI. Character-states space versus rates of evolution in phylogenetic inferences. Cladistics. 2004;20:191-204.

    Not in our library10.1111/j.1096-0031.2004.00014.x

  939. 939.

    Simon J, Laurent S, Grolleau G, Thoraval P, Soubieux D, Rasschaert D. Evolution of preproinsulin gene in birds. Molecular Phylogenetics and Evolution. 2004;30:755-766.

    Not in our library10.1016/s1055-7903(03)00254-9

  940. 940.

    Simon C, Nigro L, Sullivan J, Holsinger K, Martin A, Grapputo A, Franke A, McIntosh C. Large differences in substitutional pattern and evolutionary rate of 12S ribosomal RNA genes. Molecular Biology and Evolution. 1996;13:923-932.

    Not in our library10.1093/oxfordjournals.molbev.a025660

  941. 941.

    Simonetta AM. Cinesi e morfologiea del cranio negli uccelli non passeriformi. Studio su varie tendenze evolutive. Parte Ia. Archivio Zoologico Italiano (Torino). 1963;48:53-135.

    Not in our library

  942. 942.

    Simpson GG. Tempo and mode in evolution. 1944.

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  943. 943.

    Simpson SF, Cracraft J. The phylogenetic relationships of the Piciformes (Class Aves). Auk. 1981;98:481-494.

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  944. 944.

    Slack KE, Delsuc F, McLenachan PA, Arnason U, Penny D. Resolving the root of avian mitogenomic tree by breaking up long branches. Molecular Phylogenetics and Evolution. 2006a;42:1-13.

    Not in our library10.1016/j.ympev.2006.06.002

  945. 945.

    Slack KE, Janke A, Penny D, Amason U. Two new avian mitochondrial genomes (penguin and goose) and a summary of bird and reptile mitogenomic features. Gene. 2003;302:43-52.

    Not in our library10.1016/s0378111902010533

  946. 946.

    Slack KE, Jones CM, Ando T, Harrison GL, Fordyce RE, Arnason U, Penny D. Early penguin fossils, plus mitochondrial genomes, calibrate avian evolution. Molecular Biology and Evolution. 2006b;23:1144-1155.

    Not in our library10.1093/molbev/msj124

  947. 947.

    Slikas B. Phylogeny of the avian family Ciconiidae (storks) based on cytochrome b sequences and DNA-DNA hybridization distances. Molecular Phylogenetics and Evolution. 1997;8:275-300.

    Not in our library10.1006/mpev.1997.0431

  948. 948.

    Slikas B. Recognizing and testing homology of courtship displays in storks (Aves: Ciconiiformes: Ciconiidae). Evolution. 1998;52:884-893.

    Not in our library10.1111/j.1558-5646.1998.tb03713.x

  949. 949.

    Smith GA. Systematics of parrots. Ibis. 1975;117:18-68.

    Not in our library

  950. 950.

    Smith AB. Systematics and the fossil record: documenting evolutionary patterns. 1994.

    Not in our library

  951. 951.

    Smith AB. What does palaeontology contribute to systematics in a molecular world? Molecular Phylogenetics and Evolution. 1998;9:437-447.

    Not in our library10.1006/mpev.1998.0488

  952. 952.

    Smith EJ, Li S, Zhijian T. Gallus gallus aggrecan gene-based phylogenetic analysis of selected avian taxonomic groups. Genetica. 2005;124:23-32.

    Not in our library10.1007/s10709-004-5184-4

  953. 953.

    Smith VS, Page RDM, Johnson KP. Data incongruence and the problem of avian louse phylogeny. Zoologica Scripta. 2004;33:239-259.

    Not in our library

  954. 954.

    Smith AB, Peterson KJ. Dating the time of origin of major clades: molecular clocks and the fossil record. Annual Review of Earth and Planetary Science. 2002;30:65-88.

    Not in our library

  955. 955.

    Snively E, Russell AP, Powell GL. Evolutionary morphology of the coelurosaurian arctometatarsus: descriptive, morphometric and phylogenetic approaches. Zoological Journal of the Linnean Society. 2004;142:525-553.

    Not in our library

  956. 956.

    Sober E, Platnick NI, Funk VA. Parsimony methods in systematics. Advances in cladistics. 1982;2:37-48.

    Not in our library

  957. 957.

    Sober E, Albert VA. Parsimony and its presuppositions. Parsimony, phylogeny, and genomics. 2005;43-56.

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  958. 958.

    Sommer RJ. Convergence and the interplay of evolution and development. Evolution and Development. 1999;1:8-10.

    Not in our library10.1046/j.1525-142x.1999.99022.x

  959. 959.

    Sorenson MD. TreeRot. 1999.

    Not in our library

  960. 960.

    Sorenson MD, Cooper A, Paxinos EE, Quinn TW, James HF, Olson SL, Fleischer RC. Relationships of the extinct moa-nalos, flightless Hawaiian waterfowl, based on ancient DNA. Proceedings of the Royal Society of London (Series B). 1999;266:2187-2194.

    Not in our library10.1098/rspb.1999.0907

  961. 961.

    Sorenson MD, O’Neal E, García-Moreno J, Mindell DP. More taxa, more characters: the hoatzin problem is still unresolved. Molecular Biology and Evolution. 2003;20:1484-1499.

    Not in our library10.1093/molbev/msg157

  962. 962.

    Sorenson MD, Payne RB, Payne RB. Molecular systematics: cuckoo phylogeny inferred from mitochondrial DNA sequences. Bird families of the world: cuckoos. 2003;68-108.

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    Sraml M, Christidis L, Easteal S, Horn P, Collet C. Molecular relationships between Australian waterfowl (Anseriformes). Australian Journal of Zoology. 1996;44:47-58.

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    Stanley SE, Harrison RG. Cytochrome b evolution in birds and mammals: an evaluation of the avian constraint hypothesis. Molecular Biology and Evolution. 1999;16:1575-1585.

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    Stapel SO, Leunissen JA, Versteeg M, Wattel J, de Jong W. Ratites as oldest offshoot of avian stem – evidence from α-crystallin A sequences. Nature. 1984;311:257-259.

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  969. 969.

    Starck D. Die endocraniale Morphologie der Ratiten, besonders der Apterygidae und Dinornithidae. Gegenbaurs Morphologisches Jahrbuch. 1955;96:14-72.

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    Starck D. Parallel development and specialisation during the evolution of the bird skull. Annale Universiteit Van Stellenbosch (Série A). 1969;44:217-228.

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    Steel M, Penny D, Albert VA. Maximum parsimony and the phylogenetic information in multistate characters. Parsimony, phylogeny, and genomics. 2005;163-180.

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    Steel M, Pickett KM. On the impossibility of uniform priors on clades. Molecular Phylogenetics and Evolution. 2006;38:585-586.

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    Stegmann BK. [Über die Eigenheiten des Fluges der Pterocliden]. Zoologichesky Zhurnal. 1957;36:1521-1529.

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  975. 975.

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    Steinbacher J. Bemerkungen zur Brutbiologie, Morphologie und Anatomie von Kagu-Jungen (Rhynochetos jubatus Verreaux & Des Murs). Bonner Zoologische Beiträge. 1968;19:198-205.

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    Stidham TA. A lower jaw from a Cretaceous parrot. Nature. 1998;396:29-30.

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    Stolpe M. Colymbus, Hesperornis, Podiceps: ein Vergleich ihrer hinteren Extremität. Journal für Ornithologie. 1935;83:115-128.

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    Stonor CR. Some features of the variation of the birds of paradise. Proceedings of the Zoological Society of London. 1938;108:417-481.

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    Storer RW. The fossil loon, Colymboides minutus. Condor. 1956;58:413-426.

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    Storer RW, Marshall AJ. The classification of birds. Biology and comparative physiology of birds. 1960a;1:57-93.

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    Storer RW, Bergman G, Donner KO, von Haartman L. Evolution in the diving birds. Proceedings of the XII International Ornithological Congress. 1960b;2:694-707.

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    Storer RW, Farner DS, King JR. Adaptive radiation of birds. Avian biology. 1971a;1:149-188.

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    Storer RW. The Metazoan parasite fauna of loons (Aves: Gaviiformes), its relationship to the birds’ evolutionary history and biology, and a comparison with the parasite fauna of grebes. University of Michigan Museum of Zoology Miscellanious Publications. 2002;191:1-36.

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    Storer RW. The grebe-flamingo connection: a rebuttal. Auk. 2006;123:1183-1184.

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    Strauch JG. The phylogeny of the Charadriiformes (Aves): a new estimate using the method of character compatibility analysis. Transactions of the Zoological Society of London. 1978;34:263-345.

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    Strauch JG. The phylogeny of the Alcidae. Auk. 1985;102:520-539.

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    Suzuki N, Laskowski M, Lee YC. Phylogenetic expression of Galα1–4Gal on avian glycoproteins: glycan differentiation inscribed in the early history of modern birds. Proceedings of the National Academy of Science USA. 2004;101:9023-9028.

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  997. 997.

    Swierczewski EV, Raikow RJ. Hindlimb morphology, phylogeny, and classification of the Piciformes. Auk. 1981;98:466-480.

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  999. 999.

    Swofford DL. PAUP*: phylogenetic analysis using parsimony (*and other methods). 2002.

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    Tavares ES, Baker AJ, Pereira SL, Miyaki CY. Phylogenetic relationships and historical biogeography of Neotropical parrots (Psittaciformes: Psittacidae: Arini) inferred from mitochondrial and nuclear DNA sequences. Systematic Biology. 2006;55:454-470.

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    Taylor PG. Reproducibility of ancient DNA sequences from extinct Pleistocene fauna. Molecular Biology and Evolution. 1996;13:283-285.

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    Telford MJ. Turning Hox‘signatures’ into synapomorphies. Evolution and Development. 2000;2:360-364.

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  1023. 1023.

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  1026. 1026.

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  1029. 1029.

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  1030. 1030.

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  1031. 1031.

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  1046. 1046.

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  1049. 1049.

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    Wake DB, Bock GR, Cardew G. Homoplasy, homology, and the problem of ‘sameness’ in biology. Homology. 1999;24-46.

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  1078. 1078.

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    Wink M, Heidrich P, König C, Wieck F, Becking JH. Molecular evolution and systematics of the owls (Strigiformes). Owls: a guide to the owls of the world. 1999;39-57.

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    Winkler DW, Sheldon FH. Evolution of nest construction in swallows (Hirundinidae): a molecular phylogenetic perspective. Proceedings of the National Academy of Science USA. 1993;90:5705-5707.

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