Publications
33 results found
Brazeau M, Castiello M, El Fassi El Fehri A, et al., 2023, Fossil evidence for a pharyngeal origin of the vertebrate pectoral girdle, Nature, Vol: 623, Pages: 550-554, ISSN: 0028-0836
The origin of vertebrate paired appendages is one of the most investigated and debated examples of evolutionary novelty. Paired appendages are widely considered key innovations that allowed new opportunities for controlled swimming and gill ventilation and were prerequisites for the eventual transition from water to land. The last 150 years of debate has been shaped by two contentious theories: the ventrolateral fin-fold hypothesis and the archipterygium hypothesis. The latter proposes that fins and girdles evolved from an ancestral gill arch. Although tantalizing developmental evidence has revived interest in this idea, it is apparently unsupported by fossil evidence. Here we present fossil evidence of a pharyngeal basis for the vertebrate shoulder girdle. We use CT scanning to reveal details of the braincase of Kolymaspis sibirica, a placoderm fish from the Early Devonian of Siberia that suggests a pharyngeal component of the shoulder. We combine these findings with refreshed comparative anatomy of placoderms and jawless outgroups to place the origin of the shoulder girdle on the sixth branchial arch. These findings provide a novel framework for understanding the origin of the pectoral girdle. Our new evidence clarifies the location of the presumptive head-trunk interface in jawless fishes and explains the constraint on branchial arch number in gnathostomes. The results revive a key aspect of the archipterygium hypothesis, but also reconciles it with the ventrolateral fin fold model.
Lopez-Romero FA, Stumpf S, Kamminga P, et al., 2023, Shark mandible evolution reveals patterns of trophic and habitat-mediated diversification, Communications Biology, Vol: 6, ISSN: 2399-3642
Environmental controls of species diversity represent a central research focus in evolutionary biology. In the marine realm, sharks are widely distributed, occupying mainly higher trophic levels and varied dietary preferences, mirrored by several morphological traits and behaviours. Recent comparative phylogenetic studies revealed that sharks present a fairly uneven diversification across habitats, from reefs to deep-water. We show preliminary evidence that morphological diversification (disparity) in the feeding system (mandibles) follows these patterns, and we tested hypotheses linking these patterns to morphological specialisation. We conducted a 3D geometric morphometric analysis and phylogenetic comparative methods on 145 specimens representing 90 extant shark species using computed tomography models. We explored how rates of morphological evolution in the jaw correlate with habitat, size, diet, trophic level, and taxonomic order. Our findings show a relationship between disparity and environment, with higher rates of morphological evolution in reef and deep-water habitats. Deep-water species display highly divergent morphologies compared to other sharks. Strikingly, evolutionary rates of jaw disparity are associated with diversification in deep water, but not in reefs. The environmental heterogeneity of the offshore water column exposes the importance of this parameter as a driver of diversification at least in the early part of clade history.
Brazeau MDD, Yuan H, Giles S, et al., 2023, A well-preserved 'placoderm' (stem-group Gnathostomata) upper jaw from the Early Devonian of Mongolia clarifies jaw evolution, Royal Society Open Science, Vol: 10, ISSN: 2054-5703
The origin of jaws and teeth remains contentious in vertebrate evolution. ‘Placoderms’ (Silurian-Devonian armoured jawed fishes) are central to debates on the origins of these anatomical structures. ‘Acanthothoracids’ are generally considered the most primitive ‘placoderms’. However, they are so far known mainly from disarticulated skeletal elements that are typically incomplete. The structure of the jaws—particularly the jaw hinge—is poorly known, leaving open questions about their jaw function and comparison with other placoderms and modern gnathostomes. Here we describe a near-complete ‘acanthothoracid’ upper jaw, allowing us to reconstruct the likely orientation and angle of the bite and compare its morphology with that of other known ‘placoderm’ groups. We clarify that the bite position is located on the upper jaw cartilage rather than on the dermal cheek and thus show that there is a highly conserved bite morphology among most groups of ‘placoderms’, regardless of their overall cranial geometry. Incorporation of the dermal skeleton appears to provide a sound biomechanical basis for jaw origins. It appears that ‘acanthothoracid’ dentitions were fundamentally similar in location to that of arthrodire ‘placoderms’, rather than resembling bony fishes. Irrespective of current phylogenetic uncertainty, the new data here resolve the likely general condition for ‘placoderms’ as a whole, and as such, ancestral morphology of known jawed vertebrates.
Dearden RP, den Blaauwen JL, Sansom IJ, et al., 2021, A revision of Vernicomacanthus Miles with comments on the characters of stem-group chondrichthyans, PAPERS IN PALAEONTOLOGY, Vol: 7, Pages: 1949-1976, ISSN: 2056-2799
Brazeau MD, Giles S, Dearden RP, et al., 2020, Endochondral bone in an early devonian ‘placoderm’ from Mongolia, Nature Ecology and Evolution, Vol: 4, Pages: 1477-1484, ISSN: 2397-334X
Endochondral bone is the main internal skeletal tissue of nearly all osteichthyans—the group comprising more than 60,000 living species of bony fishes and tetrapods. Chondrichthyans (sharks and their kin) are the living sister group of osteichthyans and have primarily cartilaginous endoskeletons, long considered the ancestral condition for all jawed vertebrates (gnathostomes). The absence of bone in modern jawless fishes and the absence of endochondral ossification in early fossil gnathostomes appear to lend support to this conclusion. Here we report the discovery of extensive endochondral bone in Minjinia turgenensis, a new genus and species of ‘placoderm’-like fish from the Early Devonian (Pragian) of western Mongolia described using X-ray computed microtomography. The fossil consists of a partial skull roof and braincase with anatomical details providing strong evidence of placement in the gnathostome stem group. However, its endochondral space is filled with an extensive network of fine trabeculae resembling the endochondral bone of osteichthyans. Phylogenetic analyses place this new taxon as a proximate sister group of the gnathostome crown. These results provide direct support for theories of generalized bone loss in chondrichthyans. Furthermore, they revive theories of a phylogenetically deeper origin of endochondral bone and its absence in chondrichthyans as a secondary condition.
Castiello M, Jerve A, Burton MG, et al., 2020, Endocranial morphology of the petalichthyid placoderm Ellopetalichthys scheii from the Middle Devonian of Arctic Canada, with remarks on the inner ear and neck joint morphology of placoderms, Canadian Journal of Earth Sciences, Vol: 58, ISSN: 0008-4077
Petalichthyid and “acanthothoracid” placoderms have taken pivotal positionsin the debate on placoderm—and, by extension, jawed vertebrate—relationships owing to perceived similarities with the jawless vertebrates. Neurocranial characters are integral to current hypotheses of early gnathostome relationships. Here, we describe the three-dimensionally preserved neurocranial anatomy of the petalichthyid placoderm Ellopetalichthys scheii, from the Middle Devonian (early Eifelian) of Ellesmere Island, Canada. Using X-ray computed microtomography, we generated three-dimensional reconstructions of the endocranial surfaces, orbital walls, and cranial endocavity. These reconstructions verify the absence of a crus commune of the skeletal labyrinth and the complex shape of the petalichthyid endolympathic duct. Details of the craniothoracic joint and occipital musculature fossae help resolve the problematic comparative anatomy of the occipital surface of petalichthyids. These new data highlight similarities with arthrodire placoderms, consistent with older hypotheses of a sister-31group relationship between petalichthyids and that clade.
Brazeau M, Desjardins C, 2020, Morphy
Phylogenetic analysis of morphological characters with inapplicable data.
Brazeau MD, Guillerme T, Smith MR, 2019, An algorithm for morphological phylogenetic analysis with inapplicable data, Systematic Biology, Vol: 68, Pages: 619-631, ISSN: 1063-5157
Morphological data play a key role in the inference of biological relationships and evolutionary history and are essential for the interpretation of the fossil record. The hierarchical interdependence of many morphological characters, however, complicates phylogenetic analysis. In particular, many characters only apply to a subset of terminal taxa. The widely used “reductive coding” approach treats taxa in which a character is inapplicable as though the character’s state is simply missing (unknown). This approach has long been known to create spurious tree length estimates on certain topologies, potentially leading to erroneous results in phylogenetic searches—but pratical solutions have yet to be proposed and implemented. Here, we present a single-character algorithm for reconstructing ancestral states in reductively coded data sets, following the theoretical guideline of minimizing homoplasy over all characters. Our algorithm uses up to three traversals to score a tree, and a fourth to fully resolve final states at each node within the tree. We use explicit criteria to resolve ambiguity in applicable/inapplicable dichotomies, and to optimize missing data. So that it can be applied to single characters, the algorithm employs local optimization; as such, the method provides a fast but approximate inference of ancestral states and tree score. The application of our method to published morphological data sets indicates that, compared to traditional methods, it identifies different trees as “optimal.” As such, the use of our algorithm to handle inapplicable data may significantly alter the outcome of tree searches, modifying the inferred placement of living and fossil taxa and potentially leading to major differences in reconstructions of evolutionary history.
Giles S, Castiello M, Dearden RP, et al., 2019, Endoskeletal Trabecular Bone in a Placoderm from the Early Devonian of Mongolia, Publisher: WILEY, Pages: S127-S127, ISSN: 0362-2525
Dearden R, Stockey C, Brazeau M, 2019, The pharynx of the stem-chondrichthyan Ptomacanthus and the early evolution of the gnathostome gill skeleton, Nature Communications, Vol: 10, Pages: 1-7, ISSN: 2041-1723
The gill apparatus of gnathostomes (jawed vertebrates) is fundamental to feeding and ventilation and a focal point of classic hypotheses on the origin of jaws and paired appendages. The gill skeletons of chondrichthyans (sharks, batoids, chimaeras) have often been assumed to reflect ancestral states. However, only a handful of early chondrichthyan gill skeletons are known and palaeontological work is increasingly challenging other pre-supposed shark-like aspects of ancestral gnathostomes. Here we use computed tomography scanning to image the three-dimensionally preserved branchial apparatus in Ptomacanthus, a 415 million year old stem-chondrichthyan. Ptomacanthus had an osteichthyan-like compact pharynx with a bony operculum helping constrain the origin of an elongate elasmobranch-like pharynx to the chondrichthyan stem-group, rather than it representing an ancestral condition of the crown-group. A mixture of chondrichthyan-like and plesiomorphic pharyngeal patterning in Ptomacanthus challenges the idea that the ancestral gnathostome pharynx conformed to a morphologically complete ancestral type.
Brazeau M, Guillerme T, Smith MR, 2018, Inapp: Reconstruction of Inapplicable Discrete Characters on Phylogenetic Trees
Inapp v0.4.1 (2018/11/13) NEW FEATURESGraphical options greatly improvedTest coverage greatly improvedMINOR IMPROVEMENTSCorrected various typos in the vignette
Chen D, Alavi Y, Brazeau MD, et al., 2018, A partial lower jaw of a tetrapod from "Romer's Gap", EARTH AND ENVIRONMENTAL SCIENCE TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH, Vol: 108, Pages: 55-65, ISSN: 1755-6910
Castiello M, Brazeau MD, 2018, Neurocranial anatomy of the petalichthyid placoderm Shearsbyaspis oepiki Young revealed by X-ray computed microtomography, Palaeontology, Vol: 61, Pages: 369-389, ISSN: 0031-0239
Stem‐group gnathostomes reveal the sequence of character acquisition in the origin of modern jawed vertebrates. The petalichthyids are placoderm‐grade stem‐group gnathostomes known from both isolated skeletal material and rarer articulated specimens of one genus. They are of particular interest because of anatomical resemblances with osteostracans, the jawless sister group of jawed vertebrates. Because of this, they have become central to debates on the relationships of placoderms and the primitive cranial architecture of gnathostomes. However, among petalichthyids, only the braincase of Macropetalichthys has been studied in detail, and the diversity of neurocranial morphology in this group remains poorly documented. Using X‐ray computed microtomography, we investigated the endocranial morphology of Shearsbyaspis oepiki Young, a three‐dimensionally preserved petalichthyid from the Early Devonian of Taemas‐Wee Jasper, Australia. We generated virtual reconstructions of the external endocranial surfaces, orbital walls and cranial endocavity, including canals for major nerves and blood vessels. The neurocranium of Shearsbyaspis resembles that of Macropetalichthys, particularly in the morphology of the brain cavity, nerves and blood vessels. Many characters, including the morphology of the pituitary vein canal and the course of the trigeminal nerve, recall the morphology of osteostracans. Additionally, the presence of a parasphenoid in Shearsbyaspis (previously not known with confidence outside of arthrodires and osteichthyans) raises some questions about current proposals of placoderm paraphyly. Our detailed description of this specimen adds to the known morphological diversity of petalichthyids, and invites critical reappraisal of the phylogenetic relationships of placoderms.
Brazeau MD, Friedman M, Jerve A, et al., 2017, A three-dimensional placoderm (stem-group gnathostome) pharyngeal skeleton and its implications for primitive gnathostome pharyngeal architecture, Journal of Morphology, Vol: 278, Pages: 1220-1228, ISSN: 0362-2525
The pharyngeal skeleton is a key vertebrate anatomical system in debates on the origin of jaws and gnathostome (jawed vertebrate) feeding. Furthermore, it offers considerable potential as a source of phylogenetic data. Well‐preserved examples of pharyngeal skeletons from stem‐group gnathostomes remain poorly known. Here, we describe an articulated, nearly complete pharyngeal skeleton in an Early Devonian placoderm fish, Paraplesiobatis heinrichsi Broili, from Hunsrück Slate of Germany. Using synchrotron light tomography, we resolve and reconstruct the three‐dimensional gill arch architecture of Paraplesiobatis and compare it with other gnathostomes. The preserved pharyngeal skeleton comprises elements of the hyoid arch (probable ceratohyal) and a series of branchial arches. Limited resolution in the tomography scan causes some uncertainty in interpreting the exact number of arches preserved. However, at least four branchial arches are present. The final and penultimate arches are connected as in osteichthyans. A single median basihyal is present as in chondrichthyans. No dorsal (epibranchial or pharyngobranchial) elements are observed. The structure of the pharyngeal skeleton of Paraplesiobatis agrees well with Pseudopetalichthys from the same deposit, allowing an alternative interpretation of the latter taxon. The phylogenetic significance of Paraplesiobatis is considered. A median basihyal is likely an ancestral gnathostome character, probably with some connection to both the hyoid and the first branchial arch pair. Unpaired basibranchial bones may be independently derived in chondrichthyans and osteichthyans.
Kamminga P, De Bruin PW, Geleijns J, et al., 2017, X-ray computed tomography library of shark anatomy and lower jaw surface models, Scientific Data, Vol: 4, ISSN: 2052-4463
The cranial diversity of sharks reflects disparate biomechanical adaptations to feeding. In order to be able to investigate and better understand the ecomorphology of extant shark feeding systems, we created a x-ray computed tomography (CT) library of shark cranial anatomy with three-dimensional (3D) lower jaw reconstructions. This is used to examine and quantify lower jaw disparity in extant shark species in a separate study. The library is divided in a dataset comprised of medical CT scans of 122 sharks (Selachimorpha, Chondrichthyes) representing 73 extant species, including digitized morphology of entire shark specimens. This CT dataset and additional data provided by other researchers was used to reconstruct a second dataset containing 3D models of the left lower jaw for 153 individuals representing 94 extant shark species. These datasets form an extensive anatomical record of shark skeletal anatomy, necessary for comparative morphological, biomechanical, ecological and phylogenetic studies.
Brazeau MD, de Winter V, 2015, The hyoid arch and braincase anatomy of Acanthodes support chondrichthyan affinity of ‘acanthodians’, Proceedings of the Royal Society B: Biological Sciences, ISSN: 0962-8452
Solving the evolutionary relationships of the acanthodians is one of the key problems in reconstructing ancestral anatomical conditions for the jawed vertebrates (gnathostomes). Current debate concerns whether acanthodians are an assemblage of stem chondrichthyans, or a more generalized grade encom- passing some early stem osteichthyans. The skull anatomy of Acanthodes bronni has been pivotal in these debates, owing to tension between chondrichthyan- and osteichthyan-like models of reconstruction. We use computed tomography scanning and traditional palaeontological techniques to resolve the long- standing debate about the anatomy of the jaw suspension. We establish the correct length of the hyomandibula and show that it attaches to a process on the ventrolateral angle of the braincase below the jugular vein groove. This condition corresponds precisely to that in chondrichthyans. This character represents an unambiguously optimized synapomorphy with chondrichthyans given current gnathostome phylogenies, corroborating the growing consensus of the chondrichthyan affinity of acanthodians.
Giles S, Coates MI, Garwood RJ, et al., 2015, Endoskeletal structure in Cheirolepis (Osteichthyes, Actinopterygii), An early ray-finned fish, Palaeontology, Vol: 58, Pages: 849-870, ISSN: 1475-4983
As the sister lineage of all other actinopterygians, the Middle to Late Devonian (Eifelian–Frasnian) Cheirolepis occupies a pivotal position in vertebrate phylogeny. Although the dermal skeleton of this taxon has been exhaustively described, very little of its endoskeleton is known, leaving questions of neurocranial and fin evolution in early ray-finned fishes unresolved. The model for early actinopterygian anatomy has instead been based largely on the Late Devonian (Frasnian) Mimipiscis, preserved in stunning detail from the Gogo Formation of Australia. Here, we present re-examinations of existing museum specimens through the use of high-resolution laboratory- and synchrotron-based computed tomography scanning, revealing new details of the neuro-cranium, hyomandibula and pectoral fin endoskeleton for the Eifelian Cheirolepis trailli. These new data highlight traits considered uncharacteristic of early actinopterygians, including an uninvested dorsal aorta and imperforate propterygium, and corroborate the early divergence of Cheirolepis within actinopterygian phylogeny. These traits represent conspicuous differences between the endoskeletal structure of Cheirolepis and Mimipiscis. Additionally, we describe new aspects of the parasphenoid, vomer and scales, most notably that the scales display peg-and-socket articulation and a distinct neck. Collectively, these new data help clarify primitive conditions within ray-finned fishes, which in turn have important implications for understanding features likely present in the last common ancestor of living osteichthyans.
Brazeau MD, Friedman M, 2015, The origin and early phylogenetic history of jawed vertebrates, NATURE, Vol: 520, Pages: 490-497, ISSN: 0028-0836
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- Citations: 116
Giles S, Friedman M, Brazeau MD, 2015, Osteichthyan-like cranial conditions in an Early Devonian stem gnathostome, Nature, Vol: 520, Pages: 82-U175, ISSN: 0028-0836
The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates). A central question concerns the morphology of the last common ancestor of living jawed vertebrates, with competing hypotheses advancing either a chondrichthyan-1,2,3 or osteichthyan-like4,5 model. Here we present Janusiscus schultzei gen. et sp. nov., an Early Devonian (approximately 415 Myr ago) gnathostome from Siberia previously interpreted as a ray-finned fish6, which provides important new information about cranial anatomy near the last common ancestor of chondrichthyans and osteichthyans. The skull roof of Janusiscus resembles that of early osteichthyans, with large plates bearing vermiform ridges and partially enclosed sensory canals. High-resolution computed tomography (CT) reveals a braincase bearing characters typically associated with either chondrichthyans (large hypophyseal opening accommodating the internal carotid arteries) or osteichthyans (facial nerve exiting through jugular canal, endolymphatic ducts exiting posterior to the skull roof) but lacking a ventral cranial fissure, the presence of which is considered a derived feature of crown gnathostomes7,8. A conjunction of well-developed cranial processes in Janusiscus helps unify the comparative anatomy of early jawed vertebrate neurocrania, clarifying primary homologies in ‘placoderms’, osteichthyans and chondrichthyans. Phylogenetic analysis further supports the chondrichthyan affinities of ‘acanthodians’, and places Janusiscus and the enigmatic Ramirosuarezia9 in a polytomy with crown gnathostomes. The close correspondence between the skull roof of Janusiscus and that of osteichthyans suggests that an extensive dermal skeleton was present in the last common ancestor of jawed vertebrates4, but ambiguities arise from uncertainties in the anatomy of Ramirosuarezia. The unexpected contrast betw
Brazeau MD, Friedman M, 2014, The characters of Palaeozoic jawed vertebrates, ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Vol: 170, Pages: 779-821, ISSN: 0024-4082
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- Citations: 55
Friedman M, Brazeau MD, 2013, PALAEONTOLOGY A jaw-dropping fossil fish, NATURE, Vol: 502, Pages: 175-177, ISSN: 0028-0836
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- Citations: 7
Brazeau MD, 2013, Taking a step back: computational problems for morphological data revisited, Annual Meeting of the Society-for-Integrative-and-Comparative-Biology (SICB), Publisher: OXFORD UNIV PRESS INC, Pages: E23-E23, ISSN: 1540-7063
Brazeau MD, 2012, A revision of the anatomy of the Early Devonian jawed vertebrate Ptomacanthus anglicus Miles, PALAEONTOLOGY, Vol: 55, Pages: 355-367, ISSN: 0031-0239
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- Citations: 27
Giles S, Brazeau MD, Atwood RC, et al., 2012, ENDOSKELETAL ANATOMY OF THE STEM ACTINOPTERYGIAN <i>CHEIROLEPIS</i> REVEALED BY HIGH-RESOLUTION COMPUTED TOMOGRAPHY, 72nd Annual Meeting of the Society-of-Vertebrate-Paleontology, Publisher: TAYLOR & FRANCIS INC, Pages: 101-101, ISSN: 0272-4634
Brazeau MD, 2011, Problematic character coding methods in morphology and their effects, BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Vol: 104, Pages: 489-498, ISSN: 0024-4066
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- Citations: 126
Anderson PSL, Friedman M, Brazeau MD, et al., 2011, Initial radiation of jaws demonstrated stability despite faunal and environmental change, NATURE, Vol: 476, Pages: 206-209, ISSN: 0028-0836
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- Citations: 107
Brazeau MD, 2011, Before and beyond congruence: using phylogenetic homology to infer evolutionary process, Annual Meeting of the Society-for-Integrative-and-Comparative-Biology, Publisher: OXFORD UNIV PRESS INC, Pages: E16-E16, ISSN: 1540-7063
Friedman M, Brazeau MD, 2011, Sequences, stratigraphy and scenarios: what can we say about the fossil record of the earliest tetrapods?, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 278, Pages: 432-439, ISSN: 0962-8452
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- Citations: 22
Friedman M, Brazeau MD, 2010, A REAPPRAISAL OF THE ORIGIN AND BASAL RADIATION OF THE OSTEICHTHYES, JOURNAL OF VERTEBRATE PALEONTOLOGY, Vol: 30, Pages: 36-56, ISSN: 0272-4634
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- Citations: 81
Brazeau MD, 2009, The braincase and jaws of a Devonian 'acanthodian' and modern gnathostome origins, NATURE, Vol: 457, Pages: 305-308, ISSN: 0028-0836
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- Citations: 182
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