Publications (27)213.35 Total impact
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Article: Testing inferences in developmental evolution: the forensic evidence principle.
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ABSTRACT: Developmental evolution (DE) examines the influence of developmental mechanisms on biological evolution. Here we consider the question: "what is the evidence that allows us to decide whether a certain developmental scenario for an evolutionary change is in fact "correct" or at least falsifiable?" We argue that the comparative method linked with what we call the "forensic evidence principle" (FEP) is sufficient to conduct rigorous tests of DE scenarios. The FEP states that different genetically mediated developmental causes of an evolutionary transformation will leave different signatures in the development of the derived character. Although similar inference rules have been used in practically every empirical science, we expand this approach here in two ways: (1) we justify the validity of this principle with reference to a well-known result from mathematical physics, known as the symmetry principle, and (2) propose a specific form of the FEP for DE: given two or more developmental explanations for a certain evolutionary event, say an evolutionary novelty, then the evidence discriminating between these hypotheses will be found in the most proximal internal drivers of the derived character. Hence, a detailed description of the ancestral and derived states, and their most proximal developmental drivers are necessary to discriminate between various evolutionary developmental hypotheses. We discuss how this stepwise order of testing is necessary, establishes a formal test, and how skipping this order of examination may violate a more accurate examination of DE. We illustrate the approach with an example from avian digit evolution.Journal of Experimental Zoology Part B Molecular and Developmental Evolution 05/2012; 318(6):489-500. · 2.42 Impact Factor -
Article: Assessing arboreal adaptations of bird antecedents: testing the ecological setting of the origin of the avian flight stroke.
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ABSTRACT: The origin of avian flight is a classic macroevolutionary transition with research spanning over a century. Two competing models explaining this locomotory transition have been discussed for decades: ground up versus trees down. Although it is impossible to directly test either of these theories, it is possible to test one of the requirements for the trees-down model, that of an arboreal paravian. We test for arboreality in non-avian theropods and early birds with comparisons to extant avian, mammalian, and reptilian scansors and climbers using a comprehensive set of morphological characters. Non-avian theropods, including the small, feathered deinonychosaurs, and Archaeopteryx, consistently and significantly cluster with fully terrestrial extant mammals and ground-based birds, such as ratites. Basal birds, more advanced than Archaeopteryx, cluster with extant perching ground-foraging birds. Evolutionary trends immediately prior to the origin of birds indicate skeletal adaptations opposite that expected for arboreal climbers. Results reject an arboreal capacity for the avian stem lineage, thus lending no support for the trees-down model. Support for a fully terrestrial ecology and origin of the avian flight stroke has broad implications for the origin of powered flight for this clade. A terrestrial origin for the avian flight stroke challenges the need for an intermediate gliding phase, presents the best resolved series of the evolution of vertebrate powered flight, and may differ fundamentally from the origin of bat and pterosaur flight, whose antecedents have been postulated to have been arboreal and gliding.PLoS ONE 01/2011; 6(8):e22292. · 4.09 Impact Factor -
Article: Pentadactyl ground state of the manus of Alligator mississippiensis and insights into the evolution of digital reduction in Archosauria
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ABSTRACT: The three-fingered state of the avian manus poses intriguing questions about the evolution of digit reduction. Although digit reduction in most tetrapods appears to be the product of straightforward digit loss, avian digit reduction may have occurred with a dissociation of digit position from digit identity. The three digits of birds have the ancestral identities of I, II, and III but develop from an early pentadactyl ground state from digital anlage 2, 3, and 4. A series of hypotheses have been proposed in an attempt to explain this disparity, including a recent suggestion that the anteriormost condensation visible in the avian limb bud is in fact a vestigial structure from a hexadactyl ancestral ground state. We investigated this proposal by presenting sets of compatible evolutionary developmental trajectories starting from a hexadactyl state to test hypotheses of digit reduction. The development of skeletogenic mesenchymal condensations in a crocodylian, the closest extant relative to birds, is used to identify any extra precartiloginous digital vestiges. A developmental series of Alligator mississippiensis forelimb buds reveal only five digital anlagen, supports a pentadactyl ground state for the archosaurian manus, and rejects portions of the evolutionary developmental trajectories proposed. This condition lends further support to the contribution of a homeotic transformation during digit reduction in avian ancestry to account for the dissociation between digital identity and developmental position. J. Exp. Zool. (Mol. Dev. Evol.) 314B:571–579, 2010. © 2010 Wiley-Liss, Inc.Journal of Experimental Zoology Part B Molecular and Developmental Evolution 11/2010; 314B(7):571 - 579. · 2.42 Impact Factor -
Article: Pentadactyl ground state of the manus of Alligator mississippiensis and insights into the evolution of digital reduction in Archosauria.
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ABSTRACT: The three-fingered state of the avian manus poses intriguing questions about the evolution of digit reduction. Although digit reduction in most tetrapods appears to be the product of straightforward digit loss, avian digit reduction may have occurred with a dissociation of digit position from digit identity. The three digits of birds have the ancestral identities of I, II, and III but develop from an early pentadactyl ground state from digital anlage 2, 3, and 4. A series of hypotheses have been proposed in an attempt to explain this disparity, including a recent suggestion that the anteriormost condensation visible in the avian limb bud is in fact a vestigial structure from a hexadactyl ancestral ground state. We investigated this proposal by presenting sets of compatible evolutionary developmental trajectories starting from a hexadactyl state to test hypotheses of digit reduction. The development of skeletogenic mesenchymal condensations in a crocodylian, the closest extant relative to birds, is used to identify any extra precartiloginous digital vestiges. A developmental series of Alligator mississippiensis forelimb buds reveal only five digital anlagen, supports a pentadactyl ground state for the archosaurian manus, and rejects portions of the evolutionary developmental trajectories proposed. This condition lends further support to the contribution of a homeotic transformation during digit reduction in avian ancestry to account for the dissociation between digital identity and developmental position. J. Exp. Zool. (Mol. Dev. Evol.) 3148, 2010. (c) 2010 Wiley-Liss, Inc.Journal of Experimental Zoology Part B Molecular and Developmental Evolution 06/2010; · 2.42 Impact Factor -
Article: Low beta diversity of Maastrichtian dinosaurs of North America.
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ABSTRACT: Beta diversity is an important component of large-scale patterns of biodiversity, but its explicit examination is more difficult than that of alpha diversity. Only recently have data sets large enough been presented to begin assessing global patterns of species turnover, especially in the fossil record. We present here an analysis of beta diversity of a Maastrichtian (71-65 million years old) assemblage of dinosaurs from the Western Interior of North America, a region that covers approximately 1.5 x 10(6) km(2), borders an epicontinental sea, and spans approximately 20 degrees of latitude. Previous qualitative analyses have suggested regional groupings of these dinosaurs and generally concluded that there were multiple distinct faunal regions. However, these studies did not directly account for sampling bias, which may artificially decrease similarity and increase turnover between regions. Our analysis used abundance-based data to account for sampling intensity and was unable to support any hypothesis of multiple distinct faunas; earlier hypothesized faunal delineations were likely a sampling artifact. Our results indicate a low beta diversity and support a single dinosaur community within the entire Western Interior region of latest Cretaceous North America. Homogeneous environments are a known driver of low modern beta diversities, and the warm equable climate of the late Cretaceous modulated by the epicontenental seaway is inferred to be an underlying influence on the low beta diversity of this ancient ecosystem.Proceedings of the National Academy of Sciences 05/2010; 107(18):8265-8. · 9.68 Impact Factor -
Article: Assessing the phylogenetic utility of sequence heterochrony: evolution of avian ossification sequences as a case study.
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ABSTRACT: The evolution of developmental sequences, or sequence heterochrony, is an emerging field of study that addresses the temporal interplay between evolution and development. Some phylogenetic signal has been found in developmental sequence data, but sampling has generally been limited to small numbers of taxa and few developmental events. Here we present the largest ossification sequence dataset to date. The sequences are composed of ossification events throughout the avian skeleton, and are used to address the evolutionary signal of ossification sequence data within this clade. The results indicate that ossification sequences are conserved in birds, and show a stronger phylogenetic signal than previous studies, perhaps due to the volume of data. Phylogenetic signal is not strong enough, however, to consider ossification sequence data to be any better at resolving phylogenetic hypotheses than other morphological data and just as prone to evolutionary convergence. There is no one-to-one correlation between ossification sequence and developmental stage. We discuss some methodological implications of our findings, as well as commonalities in avian ossification sequences such as early ossification of the long bones relative to the dermatocranium, and of the hindlimb over the forelimb.Zoology 01/2010; 113(1):57-66. · 1.50 Impact Factor -
Article: Comparative ossification sequence and skeletal development of the postcranium of palaeognathous birds (Aves: Palaeognathae)
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ABSTRACT: Palaeognaths constitute one of the most basal lineages of extant birds, and are also one of the most morphologically diverse avian orders. Their skeletal development is relatively unknown, in spite of their important phylogenetic position. Here, we compare the development of the postcranial skeleton in the emu (Dromaius novaehollandiae), ostrich (Struthio camelus), greater rhea (Rhea americana) and elegant crested-tinamou (Eudromia elegans), focusing on ossification. All of these taxa are characterized by element loss in the appendicular skeleton, but there are several developmental mechanisms through which this loss occurs, including failure to chondrify, failure to ossify and fusion of cartilages prior to ossification. Further evidence is presented here to support a reduction in size of skeletal elements resulting in a delay in the timing of ossification. This study provides an important first look at the timing and sequence of postcranial ossification in palaeognathous birds, and discusses the influence of changes in the pattern of skeletal development on morphological evolution.Zoological Journal of the Linnean Society 08/2009; 157(1):169 - 196. · 2.43 Impact Factor -
Article: FOREBRAIN ENLARGEMENT AMONG NONAVIAN THEROPOD DINOSAURS
Journal of Vertebrate Paleontology 01/2009; · 2.21 Impact Factor -
Article: THE VERTEBRATE FAUNA OF THE UPPER PERMIAN OF NIGER. V. THE PRIMITIVE TEMNOSPONDYL SAHARASTEGA MORADIENSIS
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ABSTRACT: The skull of the temnospondyl amphibian Saharastega moradiensis, from the Upper Permian Moradi Formation (Izégouandane Group, Izégouandane Basin) of northwestern Niger, is described in detail. Saharastega moradiensis is the most primitive known temnospondyl from Gondwana and possesses a combination of plesiomorphic and apomorphic character states, which suggest affinities with the Edopoidea, a clade of basal temnospondyls from the Upper Carboniferous and Lower Permian of Euramerica. These include the exclusion of the lacrimal from the orbital margin, the exclusion of the vomers and palatines from the interpterygoid vacuities, and the presence of an intertemporal ossification. Autapomorphies of the new taxon include the presence of narrow and elongated, transversely oriented nostrils; an extensive tongue-and-groove contact between the premaxillae and maxillae; tabulars that possess exceptionally large, laterally and ventrally directed ‘horns’; and an extraordinary ‘occipital plate’ that may be formed, at least in part, by a supraoccipital ossification. A phylogenetic analysis of select Paleozoic temnospondyls indicates that S. moradiensis is the sister taxon to the edopoids, represented in this analysis by Chenoprosopus and Edops. This suggests that S. moradiensis represents a late-surviving member of a clade that is the sister group of the Edopoidea. Members of this clade may have been restricted to equatorial northwest Africa during the Late Carboniferous and Early Permian, an area that was not affected by the extensive glaciation that covered much of southern Pangea.Journal of Vertebrate Paleontology 01/2009; · 2.21 Impact Factor -
Article: Corrigenda: Sereno PC, Larsson HCE (2009) Cretaceous Crocodyliforms from the Sahara. ZooKeys 28: 1–143.
ZooKeys. 01/2009; -
Article: Cretaceous Crocodyliforms from the Sahara
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ABSTRACT: Diverse crocodyliforms have been discovered in recent years in Cretaceous rocks on southern landmasses formerly composing Gondwana. We report here on six species from the Sahara with an array of trophic adaptations that significantly deepen our current understanding of African crocodyliform diversity during the Cretaceous period. We describe two of these species (Anatosuchus minor, Araripesuchus wegeneri) from nearly complete skulls and partial articulated skeletons from the Lower Cretaceous Elrhaz Formation (Aptian-Albian) of Niger. The remaining four species (Araripesuchus rattoides sp. n., Kaprosuchus saharicus gen. n. sp. n., Laganosuchus thaumastos gen. n. sp. n., Laganosuchus maghrebensis gen. n. sp. n.) come from contemporaneous Upper Cretaceous formations (Cenomanian) in Niger and Morocco.ZooKeys. 01/2009; -
Article: Estimating evolution of temporal sequence changes: a practical approach to inferring ancestral developmental sequences and sequence heterochrony.
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ABSTRACT: Developmental biology often yields data in a temporal context. Temporal data in phylogenetic systematics has important uses in the field of evolutionary developmental biology and, in general, comparative biology. The evolution of temporal sequences, specifically developmental sequences, has proven difficult to examine due to the highly variable temporal progression of development. Issues concerning the analysis of temporal sequences and problems with current methods of analysis are discussed. We present here an algorithm to infer ancestral temporal sequences, quantify sequence heterochronies, and estimate pseudoreplicate consensus support for sequence changes using Parsimov-based genetic inference [PGi]. Real temporal developmental sequence data sets are used to compare PGi with currently used approaches, and PGi is shown to be the most efficient, accurate, and practical method to examine biological data and infer ancestral states on a phylogeny. The method is also expandable to address further issues in developmental evolution, namely modularity.Systematic Biology 07/2008; 57(3):378-87. · 10.23 Impact Factor -
Article: Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina.
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ABSTRACT: Living birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence. We describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia ("stomach ribs"), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax. We present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds: (1) Phase I-Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic. (2) Phase II-Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation. (3) Phase III-Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic. (4) Phase IV-Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic. In addition, we conclude: (5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation. (6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.PLoS ONE 02/2008; 3(9):e3303. · 4.09 Impact Factor -
Article: Osteology and myology of the wing of the Emu (Dromaius novaehollandiae), and its bearing on the evolution of vestigial structures.
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ABSTRACT: Emus have reduced their wing skeleton to only a single functional digit, but the myological changes associated with this reduction have never been properly described. Moreover, the intraspecific variability associated with these changes has not previously been examined, dissections having been restricted in the past to only one or two individuals. In this paper, the myology and osteology of the Emu wing is described for a sample of five female birds. The Emu showed a marked reduction in the number of muscles in the wing, even compared with other ratites. Many wing muscles showed diversity in structure, origin and insertion sites, number of heads, as well as presence-absence variation. This variability dramatically exceeds that found in flying birds. Evolutionary theory predicts that relaxed selection on vestigial organs should allow more variation to persist in the population, and corresponds to what is observed here. A large amount of fluctuating asymmetry was also detected, indicating reduced canalization of the wing during development.Journal of Morphology 05/2007; 268(5):423-41. · 1.54 Impact Factor -
Article: Osteology and myology of the wing of the Emu (Dromaius novaehollandiae), and its bearing on the evolution of vestigial structures
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ABSTRACT: Emus have reduced their wing skeleton to only a single functional digit, but the myological changes associated with this reduction have never been properly described. Moreover, the intraspecific variability associated with these changes has not previously been examined, dissections having been restricted in the past to only one or two individuals. In this paper, the myology and osteology of the Emu wing is described for a sample of five female birds. The Emu showed a marked reduction in the number of muscles in the wing, even compared with other ratites. Many wing muscles showed diversity in structure, origin and insertion sites, number of heads, as well as presence–absence variation. This variability dramatically exceeds that found in flying birds. Evolutionary theory predicts that relaxed selection on vestigial organs should allow more variation to persist in the population, and corresponds to what is observed here. A large amount of fluctuating asymmetry was also detected, indicating reduced canalization of the wing during development. J. Morphol. © 2007 Wiley-Liss, Inc.Journal of Morphology 04/2007; 268(5):423 - 441. · 1.54 Impact Factor -
Article: Evolution and homology of the astragalus in early amniotes: new fossils, new perspectives.
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ABSTRACT: The reorganization of the ankle in basal amniotes has long been considered a key innovation allowing the evolution of more terrestrial and cursorial behavior. Understanding how this key innovation arose is a complex problem that largely concerns the homologizing of the amniote astragalus with the various ossifications in the anamniote tarsus. Over the last century, several hypotheses have been advanced homologizing the amniote astragalus with the many ossifications in the ankle of amphibian-grade tetrapods. There is an emerging consensus that the amniote astragalus is a complex structure emerging via the co-ossification of several originally separate elements, but the identities of these elements remain unclear. Here we present new fossil evidence bearing on this contentious question. A poorly ossified, juvenile astragalus of the large captorhinid Moradisaurus grandis shows clear evidence of four ossification centers, rather than of three centers or one center as posited in previous models of astragalus homology. Comparative material of the captorhinid Captorhinikos chozaensis is also interpretable as demonstrating four ossification centers. A new, four-center model for the homology of the amniote astragalus is advanced, and is discussed in the context of the phylogeny of the Captorhinidae in an attempt to identify the developmental transitions responsible for the observed pattern of ossification within this clade. Lastly, the broader implications for amniote phylogeny are discussed, concluding that the neomorphic pattern of astragalus ossification seen in all extant reptiles (including turtles) arose within the clade Diapsida.Journal of Morphology 05/2006; 267(4):415-25. · 1.54 Impact Factor -
Article: Evolution and homology of the astragalus in early amniotes: New fossils, new perspectives
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ABSTRACT: The reorganization of the ankle in basal amniotes has long been considered a key innovation allowing the evolution of more terrestrial and cursorial behavior. Understanding how this key innovation arose is a complex problem that largely concerns the homologizing of the amniote astragalus with the various ossifications in the anamniote tarsus. Over the last century, several hypotheses have been advanced homologizing the amniote astragalus with the many ossifications in the ankle of amphibian-grade tetrapods. There is an emerging consensus that the amniote astragalus is a complex structure emerging via the co-ossification of several originally separate elements, but the identities of these elements remain unclear. Here we present new fossil evidence bearing on this contentious question. A poorly ossified, juvenile astragalus of the large captorhinid Moradisaurus grandis shows clear evidence of four ossification centers, rather than of three centers or one center as posited in previous models of astragalus homology. Comparative material of the captorhinid Captorhinikos chozaensis is also interpretable as demonstrating four ossification centers. A new, four-center model for the homology of the amniote astragalus is advanced, and is discussed in the context of the phylogeny of the Captorhinidae in an attempt to identify the developmental transitions responsible for the observed pattern of ossification within this clade. Lastly, the broader implications for amniote phylogeny are discussed, concluding that the neomorphic pattern of astragalus ossification seen in all extant reptiles (including turtles) arose within the clade Diapsida. J. Morphol. © 2006 Wiley-Liss, Inc.Journal of Morphology 03/2006; 267(4):415 - 425. · 1.54 Impact Factor -
Article: Permian tetrapods from the Sahara show climate-controlled endemism in Pangaea.
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ABSTRACT: New fossils from the Upper Permian Moradi Formation of northern Niger provide an insight into the faunas that inhabited low-latitude, xeric environments near the end of the Palaeozoic era (approximately 251 million years ago). We describe here two new temnospondyl amphibians, the cochleosaurid Nigerpeton ricqlesi gen. et sp. nov. and the stem edopoid Saharastega moradiensis gen. et sp. nov., as relicts of Carboniferous lineages that diverged 40-90 million years earlier. Coupled with a scarcity of therapsids, the new finds suggest that faunas from the poorly sampled xeric belt that straddled the Equator during the Permian period differed markedly from well-sampled faunas that dominated tropical-to-temperate zones to the north and south. Our results show that long-standing theories of Late Permian faunal homogeneity are probably oversimplified as the result of uneven latitudinal sampling.Nature 05/2005; 434(7035):886-9. · 36.28 Impact Factor -
Article: What is the promise of developmental evolution? III. The crucible of developmental evolution.
Journal of Experimental Zoology Part B Molecular and Developmental Evolution 01/2004; 300(1):1-4. · 2.42 Impact Factor -
Article: Pentadactyl ground state of the avian wing.
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ABSTRACT: The issue of the homology of bird fingers with those of pentadactyl amniotes has been a topic of contention for nearly 200 years. Data from the fossil record and phylogenetic systematics ascribe bird digit homologies to digits I, II, and III of pentadactyl amniotes while embryological evidence supports digital homologies of II, III, and IV. Using a molecular marker specific for condensation competent mesenchymal cells, we describe a pentadactyl arrangement of prechondrogenic digital anlagen in the wings of stage 29 chick embryos. Only the middle three anlagen develop into mature fingers. This pattern supports the hypothesis that bird fingers develop from digital anlagen II, III, and IV of pentadactylous amniotes. In addition, this result rejects a model assuming a shift in the primary axis in bird digit development and shows that a prechondrogenic digital anlage has been maintained in the bird lineage for at least 220 million years since the last known pentadactylous ancestor of the lineage. Such a vestige suggests that strong constraints are maintaining a pentadactyl ground state in amniotes.Journal of Experimental Zoology 09/2002; 294(2):146-51.
Top co-authors
Top Journals
Institutions
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2006–2012
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McGill University
- Redpath Museum
Montréal, Quebec, Canada -
New York College of Osteopathic Medicine
New York City, NY, USA
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2009–2010
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University of Alberta
- Department of Biological Sciences
Edmonton, Alberta, Canada -
Concordia University–Ann Arbor
Ann Arbor, MI, USA
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1999–2009
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University of Chicago
- Department of Organismal Biology & Anatomy
Chicago, IL, USA
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2004
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Yale University
- Department of Ecology and Evolutionary Biology
New Haven, CT, USA
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2002
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University of Toronto
Toronto, Ontario, Canada
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