1
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Jobbins M, Rücklin M, Sánchez Villagra MR, Lelièvre H, Grogan E, Szrek P, Klug C. Extreme lower jaw elongation in a placoderm reflects high disparity and modularity in early vertebrate evolution. ROYAL SOCIETY OPEN SCIENCE 2024; 11:231747. [PMID: 38298398 PMCID: PMC10827443 DOI: 10.1098/rsos.231747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 01/09/2024] [Indexed: 02/02/2024]
Abstract
Jaws are a key vertebrate feature that arose early in our evolution. Placoderms are among the first jawed vertebrates; their fossils yield essential knowledge about the early diversification of gnathostome feeding strategies, diets and modularity. Modularity can be expressed through disproportional lengths of lower and upper jaws as in swordfish or halfbeaks. Alienacanthus malkowskii is an arthrodire from the Famennian of Morocco and Poland, whose most remarkable feature is its lower jaw, which is twice as long as the skull. This is the oldest record of such extreme jaw elongation and modularity in vertebrates. The gnathal plates of Alienacanthus possess sharp, posteriorly recurved teeth that continue anterior of the occlusion in the inferognathals. The dentition suggests a catching and trapping live prey function, and the jaw occlusion is unique among placoderms. This armoured 'fish' expands the morphological and ecological diversity during one of the first radiations of jawed vertebrates with a combination of features so far unrecorded for arthrodires.
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Affiliation(s)
- Melina Jobbins
- Department of Palaeontology, University of Zurich, Karl-Schmid-Strasse 4, 8004 Zurich, Switzerland
| | - Martin Rücklin
- Naturalis Biodiversity Center, Darwinweg 2, 2333 Leiden, The Netherlands
- University of Leiden, Sylviusweg 72, 2333 Leiden, The Netherlands
| | | | - Hervé Lelièvre
- 101 Muséum National d'Histoire Naturelle, 57 rue Cuvier, 75005 Paris, France
| | - Eileen Grogan
- Department of Biology, Saint Joseph's University, 5600 City Avenue, 19131 Pennsylvania, PA, USA
| | - Piotr Szrek
- Polish Geological Institute–National Research Institute, Rakowiecka 4, 00-975 Warsaw, Poland
| | - Christian Klug
- Department of Palaeontology, University of Zurich, Karl-Schmid-Strasse 4, 8004 Zurich, Switzerland
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2
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Brazeau MD, Castiello M, El Fassi El Fehri A, Hamilton L, Ivanov AO, Johanson Z, Friedman M. Fossil evidence for a pharyngeal origin of the vertebrate pectoral girdle. Nature 2023; 623:550-554. [PMID: 37914937 PMCID: PMC10651482 DOI: 10.1038/s41586-023-06702-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 10/02/2023] [Indexed: 11/03/2023]
Abstract
The origin of vertebrate paired appendages is one of the most investigated and debated examples of evolutionary novelty1-7. Paired appendages are widely considered as key innovations that enabled new opportunities for controlled swimming and gill ventilation and were prerequisites for the eventual transition from water to land. The past 150 years of debate8-10 has been shaped by two contentious theories4,5: the ventrolateral fin-fold hypothesis9,10 and the archipterygium hypothesis8. The latter proposes that fins and girdles evolved from an ancestral gill arch. Although studies in animal development have revived interest in this idea11-13, it is apparently unsupported by fossil evidence. Here we present palaeontological support for a pharyngeal basis for the vertebrate shoulder girdle. We use computed tomography scanning to reveal details of the braincase of Kolymaspis sibirica14, an Early Devonian placoderm fish from 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 evidence clarifies the location of the presumptive head-trunk interface in jawless fishes and explains the constraint on branchial arch number in gnathostomes15. The results revive a key aspect of the archipterygium hypothesis and help reconcile it with the ventrolateral fin-fold model.
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Affiliation(s)
- Martin D Brazeau
- Department of Life Sciences, Imperial College London, Ascot, UK.
- The Natural History Museum, London, UK.
| | - Marco Castiello
- Department of Life Sciences, Imperial College London, Ascot, UK
- London Academy of Excellence, London, United Kingdom
| | - Amin El Fassi El Fehri
- Department of Life Sciences, Imperial College London, Ascot, UK
- Paläontologisches Institut und Museum, Universität Zürich, Zurich, Switzerland
| | - Louis Hamilton
- Department of Life Sciences, Imperial College London, Ascot, UK
| | - Alexander O Ivanov
- Department of Sedimentary Geology, Institute of Earth Sciences, St Petersburg State University, St Petersburg, Russia
- Institute of Geology and Petroleum Technologies, Kazan Federal University, Kazan, Russia
| | | | - Matt Friedman
- The Natural History Museum, London, UK
- Museum of Paleontology, University of Michigan, Ann Arbor, MI, USA
- Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA
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3
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Gueriau P, Parry LA, Rabet N. Gilsonicaris from the Lower Devonian Hunsrück slate is a eunicidan annelid and not the oldest crown anostracan crustacean. Biol Lett 2023; 19:20230312. [PMID: 37643644 PMCID: PMC10465189 DOI: 10.1098/rsbl.2023.0312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Accepted: 08/14/2023] [Indexed: 08/31/2023] Open
Abstract
The Lower Devonian (Lower Emsian, -400 Myr) roof slates of the Hunsrück in southeastern Germany have delivered a highly diverse and exceptionally preserved marine fauna that provides a unique snapshot into the anatomy and ecology of a wide range of Palaeozoic animals. Several of the described taxa, however, remain enigmatic in their affinity, at least until new pyritized features hidden under the surface of the slate are revealed using X-ray radiography or micro-computed tomography (µCT). Here, we redescribe such an enigmatic fossil, the putative anostracan crustacean Gilsonicaris rhenanus Van Straelen, 1943. Using µCT scanning, we unveil unprecedented details of its anatomy, including a ventral oral opening and four pairs of recalcitrant jaw elements. These jaws are morphologically consistent with the scolecodonts of eunicidan polychaetes, which along with the gross anatomy of the body and head unambiguously identifies G. rhenanus as a polychaete rather than an arthropod. While this discovery firmly discards the Early Devonian record of crown anostracans in the fossil record, it adds a new record of eunicidan soft tissues, which are surprisingly rare considering the abundant microfossil record of scolecodonts.
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Affiliation(s)
- P. Gueriau
- Université Paris-Saclay, CNRS, ministère de la Culture, UVSQ, MNHN, Institut photonique d'analyse non-destructive européen des matériaux anciens, 91192 Saint-Aubin, France
- Institute of Earth Sciences, University of Lausanne, Lausanne, Switzerland
| | - L. A. Parry
- Centre for Life's Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, UK
| | - N. Rabet
- BOREA, Sorbonne Université, Muséum national d'Histoire naturelle, Paris, France
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4
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Sellers KC, Nieto MN, Degrange FJ, Pol D, Clark JM, Middleton KM, Holliday CM. The effects of skull flattening on suchian jaw muscle evolution. Anat Rec (Hoboken) 2022; 305:2791-2822. [PMID: 35661427 DOI: 10.1002/ar.24912] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Revised: 02/28/2022] [Accepted: 03/02/2022] [Indexed: 12/20/2022]
Abstract
Jaw muscles are key features of the vertebrate feeding apparatus. The jaw musculature is housed in the skull whose morphology reflects a compromise between multiple functions, including feeding, housing sensory structures, and defense, and the skull constrains jaw muscle geometry. Thus, jaw muscle anatomy may be suboptimally oriented for the production of bite force. Crocodylians are a group of vertebrates that generate the highest bite forces ever measured with a flat skull suited to their aquatic ambush predatory style. However, basal members of the crocodylian line (e.g., Prestosuchus) were terrestrial predators with plesiomorphically tall skulls, and thus the origin of modern crocodylians involved a substantial reorganization of the feeding apparatus and its jaw muscles. Here, we reconstruct jaw muscles across a phylogenetic range of crocodylians and fossil suchians to investigate the impact of skull flattening on muscle anatomy. We used imaging data to create 3D models of extant and fossil suchians that demonstrate the evolution of the crocodylian skull, using osteological correlates to reconstruct muscle attachment sites. We found that jaw muscle anatomy in early fossil suchians reflected the ancestral archosaur condition but experienced progressive shifts in the lineage leading to Metasuchia. In early fossil suchians, musculus adductor mandibulae posterior and musculus pterygoideus (mPT) were of comparable size, but by Metasuchia, the jaw musculature is dominated by mPT. As predicted, we found that taxa with flatter skulls have less efficient muscle orientations for the production of high bite force. This study highlights the diversity and evolution of jaw muscles in one of the great transformations in vertebrate evolution.
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Affiliation(s)
- Kaleb C Sellers
- Department of Pathology and Anatomical Sciences, University of Missouri, Columbia, Missouri, USA.,Department of Clinical Anatomy and Osteopathic Principles and Practice, Rocky Vista University, Parker, Colorado, USA
| | - Mauro Nicolas Nieto
- Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), UNC, CONICET, Córdoba, Argentina
| | - Federico J Degrange
- Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), UNC, CONICET, Córdoba, Argentina
| | - Diego Pol
- CONICET, Museo Paleontológico Egidio Feruglio, Trelew, Argentina
| | - James M Clark
- Department of Biological Sciences, The George Washington University, Washington, District of Columbia, USA
| | - Kevin M Middleton
- Department of Pathology and Anatomical Sciences, University of Missouri, Columbia, Missouri, USA
| | - Casey M Holliday
- Department of Pathology and Anatomical Sciences, University of Missouri, Columbia, Missouri, USA
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5
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Huysseune A, Cerny R, Witten PE. The conundrum of pharyngeal teeth origin: the role of germ layers, pouches, and gill slits. Biol Rev Camb Philos Soc 2021; 97:414-447. [PMID: 34647411 PMCID: PMC9293187 DOI: 10.1111/brv.12805] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Revised: 09/27/2021] [Accepted: 09/29/2021] [Indexed: 12/15/2022]
Abstract
There are several competing hypotheses on tooth origins, with discussions eventually settling in favour of an 'outside-in' scenario, in which internal odontodes (teeth) derived from external odontodes (skin denticles) in jawless vertebrates. The evolution of oral teeth from skin denticles can be intuitively understood from their location at the mouth entrance. However, the basal condition for jawed vertebrates is arguably to possess teeth distributed throughout the oropharynx (i.e. oral and pharyngeal teeth). As skin denticle development requires the presence of ectoderm-derived epithelium and of mesenchyme, it remains to be answered how odontode-forming skin epithelium, or its competence, were 'transferred' deep into the endoderm-covered oropharynx. The 'modified outside-in' hypothesis for tooth origins proposed that this transfer was accomplished through displacement of odontogenic epithelium, that is ectoderm, not only through the mouth, but also via any opening (e.g. gill slits) that connects the ectoderm to the epithelial lining of the pharynx (endoderm). This review explores from an evolutionary and from a developmental perspective whether ectoderm plays a role in (pharyngeal) tooth and denticle formation. Historic and recent studies on tooth development show that the odontogenic epithelium (enamel organ) of oral or pharyngeal teeth can be of ectodermal, endodermal, or of mixed ecto-endodermal origin. Comprehensive data are, however, only available for a few taxa. Interestingly, in these taxa, the enamel organ always develops from the basal layer of a stratified epithelium that is at least bilayered. In zebrafish, a miniaturised teleost that only retains pharyngeal teeth, an epithelial surface layer with ectoderm-like characters is required to initiate the formation of an enamel organ from the basal, endodermal epithelium. In urodele amphibians, the bilayered epithelium is endodermal, but the surface layer acquires ectodermal characters, here termed 'epidermalised endoderm'. Furthermore, ectoderm-endoderm contacts at pouch-cleft boundaries (i.e. the prospective gill slits) are important for pharyngeal tooth initiation, even if the influx of ectoderm via these routes is limited. A balance between sonic hedgehog and retinoic acid signalling could operate to assign tooth-initiating competence to the endoderm at the level of any particular pouch. In summary, three characters are identified as being required for pharyngeal tooth formation: (i) pouch-cleft contact, (ii) a stratified epithelium, of which (iii) the apical layer adopts ectodermal features. These characters delimit the area in which teeth can form, yet cannot alone explain the distribution of teeth over the different pharyngeal arches. The review concludes with a hypothetical evolutionary scenario regarding the persisting influence of ectoderm on pharyngeal tooth formation. Studies on basal osteichthyans with less-specialised types of early embryonic development will provide a crucial test for the potential role of ectoderm in pharyngeal tooth formation and for the 'modified outside-in' hypothesis of tooth origins.
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Affiliation(s)
- Ann Huysseune
- Research Group Evolutionary Developmental Biology, Biology Department, Ghent University, K.L. Ledeganckstraat 35, Ghent, B-9000, Belgium
| | - Robert Cerny
- Department of Zoology, Faculty of Science, Charles University, Vinicna 7, Prague, 128 44, Czech Republic
| | - P Eckhard Witten
- Research Group Evolutionary Developmental Biology, Biology Department, Ghent University, K.L. Ledeganckstraat 35, Ghent, B-9000, Belgium
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6
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Coatham SJ, Vinther J, Rayfield EJ, Klug C. Was the Devonian placoderm Titanichthys a suspension feeder? ROYAL SOCIETY OPEN SCIENCE 2020; 7:200272. [PMID: 32537223 PMCID: PMC7277245 DOI: 10.1098/rsos.200272] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 04/23/2020] [Indexed: 05/08/2023]
Abstract
Large nektonic suspension feeders have evolved multiple times. The apparent trend among apex predators for some evolving into feeding on small zooplankton is of interest for understanding the associated shifts in anatomy and behaviour, while the spatial and temporal distribution gives clues to an inherent relationship with ocean primary productivity and how past and future perturbations to these may impact on the different tiers of the food web. The evolution of large nektonic suspension feeders-'gentle giants'-occurred four times among chondrichthyan fishes (e.g. whale sharks, basking sharks and manta rays), as well as in baleen whales (mysticetes), the Mesozoic pachycormid fishes and at least twice in radiodontan stem group arthropods (Anomalocaridids) during the Cambrian explosion. The Late Devonian placoderm Titanichthys has tentatively been considered to have been a megaplanktivore, primarily due to its gigantic size and narrow, edentulous jaws while no suspension-feeding apparatus have ever been reported. Here, the potential for microphagy and other feeding behaviours in Titanichthys is assessed via a comparative study of jaw mechanics in Titanichthys and other placoderms with presumably differing feeding habits (macrophagy and durophagy). Finite-element models of the lower jaws of Titanichthys termieri in comparison to Dunkleosteus terrelli and Tafilalichthys lavocati reveal considerably less resistance to von Mises stress in this taxon. Comparisons with a selection of large-bodied extant taxa of similar ecological diversity reveal similar disparities in jaw stress resistance. Our results, therefore, conform to the hypothesis that Titanichthys was a suspension feeder with jaws ill-suited for biting and crushing but well suited for gaping ram feeding.
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Affiliation(s)
- Samuel J. Coatham
- Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol, UK
- Author for correspondence: Samuel J. Coatham e-mail:
| | - Jakob Vinther
- Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol, UK
| | - Emily J. Rayfield
- Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol, UK
| | - Christian Klug
- Paläontologisches Institut und Museum, Universität Zürich, Karl-Schmid-Strasse 4, 8006Zürich, Switzerland
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7
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Zhu YA, Lu J, Zhu M. Reappraisal of the Silurian placoderm Silurolepis and insights into the dermal neck joint evolution. ROYAL SOCIETY OPEN SCIENCE 2019; 6:191181. [PMID: 31598327 PMCID: PMC6774982 DOI: 10.1098/rsos.191181] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Accepted: 08/20/2019] [Indexed: 05/15/2023]
Abstract
Silurolepis platydorsalis, a Silurian jawed vertebrate originally identified as an antiarch, is here redescribed as a maxillate placoderm close to Qilinyu and is anteroposteriorly reversed as opposed to the original description. The cuboid trunk shield possesses three longitudinal cristae, obstanic grooves on the trunk shield and three median dorsal plates, all uniquely shared with Qilinyu. Further preparation reveals the morphology of the dermal neck joint, with slot-shaped articular fossae on the trunk shield similar to Qilinyu and antiarchs. However, new tomographic data reveal that Qilinyu uniquely bears a dual articulation between the skull roof and trunk shield, which does not fit into the traditional 'ginglymoid' and 'reverse ginglymoid' categories. An extended comparison in early jawed vertebrates confirms that a sliding-type dermal neck joint is widely distributed and other types are elaborated in different lineages by developing various laminae. Nine new characters related to the dermal neck joint are proposed for a new phylogenetic analysis, in which Silurolepis forms a clade with Qilinyu. The current phylogenetic framework conflicts with the parsimonious evolution of dermal neck joints in suggesting that the shared trunk shield characters between antiarchs and Qilinyu are independently acquired, and the sliding-type joint in Entelognathus is reversely evolved from the dual articulation in Qilinyu.
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Affiliation(s)
- You-an Zhu
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), 142 Xi-zhi-men-wai Street, Beijing 100044, People's Republic of China
- CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, People's Republic of China
- Subdepartment of Evolution and Development, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden
| | - Jing Lu
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), 142 Xi-zhi-men-wai Street, Beijing 100044, People's Republic of China
- CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, People's Republic of China
| | - Min Zhu
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), 142 Xi-zhi-men-wai Street, Beijing 100044, People's Republic of China
- CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, People's Republic of China
- College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
- Author for correspondence: Min Zhu e-mail:
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8
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The pharynx of the stem-chondrichthyan Ptomacanthus and the early evolution of the gnathostome gill skeleton. Nat Commun 2019; 10:2050. [PMID: 31053719 PMCID: PMC6499890 DOI: 10.1038/s41467-019-10032-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Accepted: 04/10/2019] [Indexed: 11/25/2022] Open
Abstract
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. Our understanding of the origin of jaws is hampered by the poor fossil preservation of pharyngeal morphology. Here, Dearden et al. provide insight into the skull conditions of early jawed vertebrates through three-dimensional computed tomography imaging of a 415 million year old stem-chondrichthyan.
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9
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Coates MI, Finarelli JA, Sansom IJ, Andreev PS, Criswell KE, Tietjen K, Rivers ML, La Riviere PJ. An early chondrichthyan and the evolutionary assembly of a shark body plan. Proc Biol Sci 2019; 285:rspb.2017.2418. [PMID: 29298937 DOI: 10.1098/rspb.2017.2418] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Accepted: 11/29/2017] [Indexed: 11/12/2022] Open
Abstract
Although relationships among the major groups of living gnathostomes are well established, the relatedness of early jawed vertebrates to modern clades is intensely debated. Here, we provide a new description of Gladbachus, a Middle Devonian (Givetian approx. 385-million-year-old) stem chondrichthyan from Germany, and one of the very few early chondrichthyans in which substantial portions of the endoskeleton are preserved. Tomographic and histological techniques reveal new details of the gill skeleton, hyoid arch and jaws, neurocranium, cartilage, scales and teeth. Despite many features resembling placoderm or osteichthyan conditions, phylogenetic analysis confirms Gladbachus as a stem chondrichthyan and corroborates hypotheses that all acanthodians are stem chondrichthyans. The unfamiliar character combination displayed by Gladbachus, alongside conditions observed in acanthodians, implies that pre-Devonian stem chondrichthyans are severely under-sampled and strongly supports indications from isolated scales that the gnathostome crown group originated at the latest by the early Silurian (approx. 440 Ma). Moreover, phylogenetic results highlight the likely convergent evolution of conventional chondrichthyan conditions among earliest members of this primary gnathostome division, while skeletal morphology points towards the likely suspension feeding habits of Gladbachus, suggesting a functional origin of the gill slit condition characteristic of the vast majority of living and fossil chondrichthyans.
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Affiliation(s)
- Michael I Coates
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637-1508, USA
| | - John A Finarelli
- UCD School of Biology and Environmental Science, UCD Science Education and Research Centre (West), UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland
| | - Ivan J Sansom
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Plamen S Andreev
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Katharine E Criswell
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637-1508, USA.,Department of Zoology, Cambridge University, Cambridge CB2 3EJ, UK
| | - Kristen Tietjen
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637-1508, USA
| | - Mark L Rivers
- Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637-1508, USA
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10
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Brazeau MD, Friedman M, Jerve A, Atwood RC. A three-dimensional placoderm (stem-group gnathostome) pharyngeal skeleton and its implications for primitive gnathostome pharyngeal architecture. J Morphol 2017; 278:1220-1228. [PMID: 28543631 PMCID: PMC5575467 DOI: 10.1002/jmor.20706] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2017] [Revised: 04/22/2017] [Accepted: 04/26/2017] [Indexed: 11/30/2022]
Abstract
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.
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Affiliation(s)
- Martin D Brazeau
- Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, SL5 7PY, United Kingdom.,Department of Earth Sciences, Natural History Museum, London, SW7 5BD, United Kingdom
| | - Matt Friedman
- Museum of Paleontology and Department of Earth and Environmental Sciences, University of Michigan, 1109 Geddes Ave, Ann Arbor, Michigan, 48109-1079
| | - Anna Jerve
- Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, SL5 7PY, United Kingdom
| | - Robert C Atwood
- Beamline I12-JEEP, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire, UK, OX11 0DE
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