1
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Pusch LC, Kammerer CF, Fröbisch J. The origin and evolution of Cynodontia (Synapsida, Therapsida): Reassessment of the phylogeny and systematics of the earliest members of this clade using 3D-imaging technologies. Anat Rec (Hoboken) 2024; 307:1634-1730. [PMID: 38444024 DOI: 10.1002/ar.25394] [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: 10/12/2023] [Revised: 01/13/2024] [Accepted: 01/14/2024] [Indexed: 03/07/2024]
Abstract
The origin of cynodonts, the group ancestral to and including mammals, is one of the major outstanding problems in therapsid evolution. One of the most troubling aspects of the cynodont fossil record is the lengthy Permian ghost lineage between the latest possible divergence from its sister group Therocephalia and the first appearance of definitive cynodonts in the late Permian. The absence of cynodonts and dominance of therocephalians in middle Permian strata has led some workers to argue that cynodonts evolved from within therocephalians, rendering the latter paraphyletic, but more recent analyses support the reciprocal monophyly of Cynodontia and Therocephalia. Furthermore, although a fundamental dichotomy in the derived subclade Eucynodontia is well-supported in cynodont phylogeny, the relationships of more stemward cynodonts from the late Permian and Early Triassic are unresolved. Here, we provide a re-evaluation of the phylogeny of Eutheriodontia (Cynodontia + Therocephalia) and an assessment of character evolution within the group. Using computed tomographic data derived from extensive sampling of the earliest known (late Permian and Early Triassic) cynodonts and selected exemplars of therocephalians and later (Middle Triassic onwards) cynodonts, we describe novel aspects of the endocranial anatomy of these animals. These data were incorporated into a new phylogenetic data set including a comprehensive sample of early cynodonts. Our phylogenetic analyses support some results previously recovered by other authors, but recover therocephalians as paraphyletic with regards to cynodonts, with cynodonts and eutherocephalians forming a clade to the exclusion of the "basal therocephalian" families Lycosuchidae and Scylacosauridae. Though both conservatism and homoplasy mark the endocranial anatomy of early non-mammalian cynodonts, we were able to identify several new endocranial synapomorphies for eutheriodont subclades and recovered generally better-supported topologies than previous analyses using primarily external craniodental characters.
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Affiliation(s)
- Luisa C Pusch
- Museum für Naturkunde, Leibniz-Institut füsr Evolutions- und Biodiversitätsforschung, Berlin, Germany
- Institut für Biologie, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Christian F Kammerer
- North Carolina Museum of Natural Sciences, Raleigh, North Carolina, USA
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Jörg Fröbisch
- Museum für Naturkunde, Leibniz-Institut füsr Evolutions- und Biodiversitätsforschung, Berlin, Germany
- Institut für Biologie, Humboldt-Universität zu Berlin, Berlin, Germany
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
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2
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Lund ES, Norton LA, Benoit J. First CT-assisted study of the palate and postcrania of Diarthrognathus broomi (Cynodontia, Probainognathia). Anat Rec (Hoboken) 2024; 307:1538-1558. [PMID: 38131650 DOI: 10.1002/ar.25363] [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: 07/28/2023] [Revised: 11/19/2023] [Accepted: 11/21/2023] [Indexed: 12/23/2023]
Abstract
Diarthrognathus broomi is a transitional taxon between non-mammaliaform cynodonts and Mammaliaformes that occurred during the Late Triassic to Early Jurassic. All known specimens of Diarthrognathus represent juveniles, and the postcrania have not been thoroughly described. The palatal, basicranial and postcranial elements of the referred specimen NMQR 1535 are described here for the first time using 3D reconstructions generated from X-ray micro-computed tomography (μCT) data. The presence of a large interpterygoid vacuity, open medial suture between the vomers and medially unossified secondary palate all support the interpretation that NMQR 1535 is a juvenile. In addition, Diarthrognathus uniquely possesses "suborbital" vacuities, which distinguishes it from every other known cynodont. The presence of an ossified olecranon process, among other features, suggests that Diarthrognathus may have been a scratch-digger. The postcranial skeleton of Diarthrognathus appears to be more plesiomorphic than tritylodontids, Brasilodon and other tritheledontids as, among other traits, it retains amphicoelous vertebrae. However, this taxon also displays synapomorphies with the more derived cynodonts, such as the mammalian pattern of neurocentral ossification and possible absence of an ectepicondylar foramen.
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Affiliation(s)
- Erin S Lund
- Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Luke A Norton
- Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Julien Benoit
- Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
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3
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Lautenschlager S, Fagan MJ, Luo ZX, Bird CM, Gill P, Rayfield EJ. Functional reorganisation of the cranial skeleton during the cynodont-mammaliaform transition. Commun Biol 2023; 6:367. [PMID: 37046052 PMCID: PMC10097706 DOI: 10.1038/s42003-023-04742-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Accepted: 03/21/2023] [Indexed: 04/14/2023] Open
Abstract
Skeletal simplification occurred in multiple vertebrate clades over the last 500 million years, including the evolution from premammalian cynodonts to mammals. This transition is characterised by the loss and reduction of cranial bones, the emergence of a novel jaw joint, and the rearrangement of the jaw musculature. These modifications have long been hypothesised to increase skull strength and efficiency during feeding. Here, we combine digital reconstruction and biomechanical modelling to show that there is no evidence for an increase in cranial strength and biomechanical performance. Our analyses demonstrate the selective functional reorganisation of the cranial skeleton, leading to reduced stresses in the braincase and the skull roof but increased stresses in the zygomatic region through this transition. This cranial functional reorganisation, reduction in mechanical advantage, and overall miniaturisation in body size are linked with a dietary specialisation to insectivory, permitting the subsequent morphological and ecological diversification of the mammalian lineage.
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Affiliation(s)
- Stephan Lautenschlager
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK.
| | | | - Zhe-Xi Luo
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, USA
| | - Charlotte M Bird
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Pamela Gill
- Earth Sciences Department, The Natural History Museum, London, UK
- Bristol Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol, UK
| | - Emily J Rayfield
- Bristol Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol, UK.
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4
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Abdala F, Norton LA, Jasinoski SC, Botha J, Fernandez V, Rubidge B, Gill PG, Martinelli AG. On taxonomic issues, ontogenetic series and tooth replacement. Comments on Diphyodont tooth replacement of Brasilodon-A late Triassic eucynodont that challenges the time of origin of mammals by Cabreira et al. J Anat 2023; 242:737-742. [PMID: 36715111 PMCID: PMC10008281 DOI: 10.1111/joa.13803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 11/23/2022] [Indexed: 01/31/2023] Open
Affiliation(s)
- Fernando Abdala
- Unidad Ejecutora Lillo (CONICET-Fundación Miguel Lillo), Tucumán, Argentina.,Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Luke A Norton
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Sandra C Jasinoski
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Jennifer Botha
- National Museum, Bloemfontein, South Africa.,Department of Zoology and Entomology, University of the Free State, Bloemfontein, South Africa
| | - Vincent Fernandez
- European Synchrotron Radiation Facility, Structure of Materials Department, Grenoble, France
| | - Bruce Rubidge
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Pamela G Gill
- School of Earth Sciences, University of Bristol, Bristol, UK.,Department of Earth Sciences, Natural History Museum London, London, UK
| | - Agustín G Martinelli
- Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"-Consejo Nacional de Investigaciones Científicas y Técnicas (MACN-CONICET), Ciudad Autónoma de Buenos Aires, Argentina
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5
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A complete skull of a stem mammal from the Late Triassic of Brazil illuminates the early evolution of prozostrodontian cynodonts. J MAMM EVOL 2023. [DOI: 10.1007/s10914-022-09648-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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6
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Wynd B, Abdala F, Nesbitt SJ. Ontogenetic growth in the crania of Exaeretodon argentinus (Synapsida: Cynodontia) captures a dietary shift. PeerJ 2022; 10:e14196. [PMID: 36299507 PMCID: PMC9590418 DOI: 10.7717/peerj.14196] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Accepted: 09/15/2022] [Indexed: 01/26/2023] Open
Abstract
Background An ontogenetic niche shift in vertebrates is a common occurrence where ecology shifts with morphological changes throughout growth. How ecology shifts over a vertebrate's lifetime is often reconstructed in extant species-by combining observational and skeletal data from growth series of the same species-because interactions between organisms and their environment can be observed directly. However, reconstructing shifts using extinct vertebrates is difficult and requires well-sampled growth series, specimens with relatively complete preservation, and easily observable skeletal traits associated with ecologies suspected to change throughout growth, such as diet. Methods To reconstruct ecological changes throughout the growth of a stem-mammal, we describe changes associated with dietary ecology in a growth series of crania of the large-bodied (∼2 m in length) and herbivorous form, Exaeretodon argentinus (Cynodontia: Traversodontidae) from the Late Triassic Ischigualasto Formation, San Juan, Argentina. Nearly all specimens were deformed by taphonomic processes, so we reconstructed allometric slope using a generalized linear mixed effects model with distortion as a random effect. Results Under a mixed effects model, we find that throughout growth, E. argentinus reduced the relative length of the palate, postcanine series, orbits, and basicranium, and expanded the relative length of the temporal region and the height of the zygomatic arch. The allometric relationship between the zygomatic arch and temporal region with the total length of the skull approximate the rate of growth for feeding musculature. Based on a higher allometric slope, the zygoma height is growing relatively faster than the length of the temporal region. The higher rate of change in the zygoma may suggest that smaller individuals had a crushing-dominated feeding style that transitioned into a chewing-dominated feeding style in larger individuals, suggesting a dietary shift from possible faunivory to a more plant-dominated diet. Dietary differentiation throughout development is further supported by an increase in sutural complexity and a shift in the orientation of microwear anisotropy between small and large individuals of E. argentinus. A developmental transition in the feeding ecology of E. argentinus is reflective of the reconstructed dietary transition across Gomphodontia, wherein the earliest-diverging species are inferred as omnivorous and the well-nested traversodontids are inferred as herbivorous, potentially suggesting that faunivory in immature individuals of the herbivorous Traversodontidae may be plesiomorphic for the clade.
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Affiliation(s)
- Brenen Wynd
- Department of Geosciences, Virginia Tech, Blacksburg, VA, United States of America
| | - Fernando Abdala
- CONICET-Fundación Miguel Lillo, Unidad Ejecutora Lillo, San Miguel de Tucumán, Tucumán, Argentina
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Sterling J. Nesbitt
- Department of Geosciences, Virginia Tech, Blacksburg, VA, United States of America
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7
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Duhamel A, Benoit J, Day M, Rubidge B, Fernandez V. Computed Tomography elucidates ontogeny within the basal therapsid clade Biarmosuchia. PeerJ 2021; 9:e11866. [PMID: 34527434 PMCID: PMC8403480 DOI: 10.7717/peerj.11866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Accepted: 07/05/2021] [Indexed: 11/20/2022] Open
Abstract
Biarmosuchia is a clade of basal therapsids that includes forms possessing plesiomorphic ‘pelycosaurian’ cranial characters as well as the highly derived Burnetiamorpha which are characterised by cranial pachyostosis and a variety of cranial bosses. Potential ontogenetic variation in these structures has been suggested based on growth series of other therapsids with pachyostosed crania, which complicates burnetiamorph taxonomic distinction and thus it is essential to better understand cranial ontogeny of the Burnetiamorpha. Here, three new juvenile biarmosuchian skulls from the late Permian of South Africa are described using X-ray micro computed tomography (CT). We found that juvenile biarmosuchians are distinguished from adults by their relatively large orbits, open cranial sutures, and incomplete ossification of the braincase and bony labyrinth. Also, they manifest multiple centres of ossification within the parietal and preparietal bones. CT examination reveals that the holotype of Lemurosaurus pricei (BP/1/816), previously alleged to be a juvenile, shows no evidence of juvenility and is thus probably an adult. This suggests that the larger skull NMQR 1702, previously considered to be an adult L. pricei, may represent a new taxon. This study provides, for the first time, a list of characters by which to recognise juvenile biarmosuchians.
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Affiliation(s)
- Aliénor Duhamel
- ENS de Lyon, CNRS, UMR 5276, LGL-TPE, Université Claude Bernard (Lyon I), Lyon, France.,Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.,School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Julien Benoit
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.,School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Michael Day
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.,Department of Earth Sciences, Natural History Museum, London, United Kingdom
| | - Bruce Rubidge
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.,School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Vincent Fernandez
- Department of Earth Sciences, Natural History Museum, London, United Kingdom.,European Synchrotron Radiation Facility, Grenoble, France
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8
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Norton LA, Abdala F, Rubidge BS, Botha J. Tooth replacement patterns in the Early Triassic epicynodont Galesaurus planiceps (Therapsida, Cynodontia). PLoS One 2020; 15:e0243985. [PMID: 33378326 PMCID: PMC7773207 DOI: 10.1371/journal.pone.0243985] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Accepted: 12/02/2020] [Indexed: 01/13/2023] Open
Abstract
Sixteen specimens of the Early Triassic cynodont Galesaurus planiceps (including eight that were scanned using micro-computed tomography) representing different ontogenetic stages were assembled to study the dental replacement in the species. The growth series shows that the incisors and postcanines continue to develop and replace, even in the largest (presumably oldest) specimen. In contrast, replacement of the canines ceased with the attainment of skeletal maturity, at a basal skull length of ~90 mm, suggesting that Galesaurus had a finite number of canine replacement cycles. Additionally, the functional canine root morphology of these larger specimens showed a tendency to be open-rooted, a condition not previously reported in Mesozoic theriodonts. An alternating pattern of tooth replacement was documented in the maxillary and mandibular postcanine series. Both postcanine series increased in tooth number as the skull lengthened, with the mandibular postcanine series containing more teeth than the maxillary series. In the maxilla, the first postcanine is consistently the smallest tooth, showing a proportional reduction in size as skull length increased. The longer retention of a tooth in this first locus is a key difference between Galesaurus and Thrinaxodon, in which the mesial-most postcanines are lost after replacement. This difference has contributed to the lengthening of the postcanine series in Galesaurus, as teeth continued to be added to the distal end of the tooth row through ontogeny. Overall, there are considerable differences between Galesaurus and Thrinaxodon relating to the replacement and development of their teeth.
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Affiliation(s)
- Luke A. Norton
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
- School of Geosciences, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
- * E-mail:
| | - Fernando Abdala
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
- Unidad Ejecutora Lillo (CONICET-Fundación Miguel Lillo), Tucumán, Argentina
| | - Bruce S. Rubidge
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
- School of Geosciences, University of the Witwatersrand, Johannesburg, Gauteng, South Africa
| | - Jennifer Botha
- Karoo Palaeontology, National Museum, Bloemfontein, Free State, South Africa
- Department of Zoology and Entomology, University of the Free State, Bloemfontein, Free State, South Africa
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9
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Kammerer CF, Deutsch M, Lungmus JK, Angielczyk KD. Effects of taphonomic deformation on geometric morphometric analysis of fossils: a study using the dicynodont Diictodon feliceps (Therapsida, Anomodontia). PeerJ 2020; 8:e9925. [PMID: 33083110 PMCID: PMC7547620 DOI: 10.7717/peerj.9925] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 08/21/2020] [Indexed: 01/06/2023] Open
Abstract
Taphonomic deformation, the distortion of fossils as a result of geological processes, poses problems for the use of geometric morphometrics in addressing paleobiological questions. Signal from biological variation, such as ontogenetic trends and sexual dimorphism, may be lost if variation from deformation is too high. Here, we investigate the effects of taphonomic deformation on geometric morphometric analyses of the abundant, well known Permian therapsid Diictodon feliceps. Distorted Diictodon crania can be categorized into seven typical styles of deformation: lateral compression, dorsoventral compression, anteroposterior compression, “saddle-shape” deformation (localized collapse at cranial mid-length), anterodorsal shear, anteroventral shear, and right/left shear. In simulated morphometric datasets incorporating known “biological” signals and subjected to uniform shear, deformation was typically the main source of variance but accurate “biological” information could be recovered in most cases. However, in empirical datasets, not only was deformation the dominant source of variance, but little structure associated with allometry and sexual dimorphism was apparent, suggesting that the more varied deformation styles suffered by actual fossils overprint biological variation. In a principal component analysis of all anomodont therapsids, deformed Diictodon specimens exhibit significant dispersion around the “true” position of this taxon in morphospace based on undistorted specimens. The overall variance associated with deformation for Anomodontia as a whole is minor, and the major axes of variation in the study sample show a strong phylogenetic signal instead. Although extremely problematic for studying variation in fossil taxa at lower taxonomic levels, the cumulative effects of deformation in this study are shown to be random, and inclusion of deformed specimens in higher-level analyses of morphological disparity are warranted. Mean morphologies of distorted specimens are found to approximate the morphology of undistorted specimens, so we recommend use of species-level means in higher-level analyses when possible.
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Affiliation(s)
| | | | - Jacqueline K Lungmus
- Field Museum of Natural History, Chicago, IL, USA.,University of Chicago, Chicago, IL, USA
| | - Kenneth D Angielczyk
- Field Museum of Natural History, Chicago, IL, USA.,University of Chicago, Chicago, IL, USA
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10
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Abdala F, Gaetano LC, Smith RMH, Rubidge BS. A new large cynodont from the Late Permian (Lopingian) of the South African Karoo Basin and its phylogenetic significance. Zool J Linn Soc 2019. [DOI: 10.1093/zoolinnean/zlz004] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Abstract
The Karoo Basin of South Africa has the best global record of Lopingian (Late Permian) non-mammaliaform cynodonts, currently represented by five species. We describe Vetusodon elikhulu gen. et sp. nov., documented by four specimens from the Daptocephalus Assemblage Zone. With a basal skull length of ~18 cm, it is the largest Lopingian cynodont and is also larger than Induan representatives of the group. Vetusodon elikhulu has a cranial morphology that departs notably from that previously documented for Permo-Triassic cynodonts. It features a short and extremely wide snout, resembling that of the contemporaneous therocephalian Moschorhinus, and has large incisors and canines that contrast with the small unicusped postcanines, suggesting a more important role of the anterior dentition for feeding. The dentary is extremely long and robust, with the posterior margin located closer to the craniomandibular joint than in other Lopingian and Induan cynodonts (e.g. Thrinaxodon). The secondary palate morphology of V. elikhulu is unique, being short and incomplete and with the posterior portion of the maxilla partly covering the vomer. A phylogenetic analysis suggests that V. elikhulu is the sister taxon of Eucynodontia and thus the most derived of the Lopingian to Induan cynodonts yet discovered.
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Affiliation(s)
- Fernando Abdala
- Unidad Ejecutora Lillo, Conicet-Fundación Miguel Lillo, Tucumán, Argentina
- Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Leandro C Gaetano
- Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
- Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Instituto de Estudios Andinos ‘Don Pablo Groeber’, IDEAN (Universidad de Buenos Aires, CONICET), Intendente Güiraldes, Ciudad Universitaria – Pabellón II, C1428EGA, Ciudad Autónoma de Buenos Aires, Argentina
| | - Roger M H Smith
- Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
- Department of Karoo Palaeontology, Iziko South African Museum, Cape Town, South Africa
| | - Bruce S Rubidge
- Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
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11
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Navarro-Díaz A, Esteve-Altava B, Rasskin-Gutman D. Disconnecting bones within the jaw-otic network modules underlies mammalian middle ear evolution. J Anat 2019; 235:15-33. [PMID: 30977522 DOI: 10.1111/joa.12992] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/06/2019] [Indexed: 01/08/2023] Open
Abstract
The origin of the mammalian middle ear ossicles from the craniomandibular articulation of their synapsid ancestors is a key event in the evolution of vertebrates. The richness of the fossil record and the multitude of developmental studies have provided a stepwise reconstruction of this evolutionary innovation, highlighting the homology between the quadrate, articular, pre-articular and angular bones of early synapsids with the incus, malleus, gonial and ectotympanic bones of derived mammals, respectively. There are several aspects involved in this functional exaptation: (i) an increase of the masticatory musculature; (ii) the separation of the quadrate bone from the cranium; and (iii) the disconnection of the post-dentary bones from the dentary. Here, we compared the jaw-otic complex for 43 synapsid taxa using anatomical network analysis, showing that the disconnection of mandibular bones was a key step in the mammalian middle ear evolution, changing the skull anatomical modularity concomitant to the acquisition of new functions. Furthermore, our analysis allows the identification of three types of anatomical modules evolving through five evolutionary stages during the anatomical transformation of the jawbones into middle ear bones, with the ossification and degradation of Meckel's cartilage in mammals as the key ontogenetic event leading the change of anatomical modularity.
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Affiliation(s)
- Aitor Navarro-Díaz
- Paleobiology and Theoretical biology (Theoretical Biology), Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain
| | - Borja Esteve-Altava
- Institute of Evolutionary Biology (UPF-CSIC), Department of Experimental and Health Sciences, University Pompeu Fabra, Barcelona, Spain
| | - Diego Rasskin-Gutman
- Paleobiology and Theoretical biology (Theoretical Biology), Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain
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12
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Pusch LC, Kammerer CF, Fröbisch J. Cranial anatomy of the early cynodont Galesaurus planiceps and the origin of mammalian endocranial characters. J Anat 2019; 234:592-621. [PMID: 30772942 DOI: 10.1111/joa.12958] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/16/2019] [Indexed: 12/19/2022] Open
Abstract
The cranial anatomy of the early non-mammalian cynodont Galesaurus planiceps from the South African Karoo Basin is redescribed on the basis of a computed tomographic reconstruction of the skull. Previously, little was known about internal skull morphology and the nervous and sensory system of this taxon. The endocranial anatomy of various cynodonts has been intensively studied in recent years to understand the origin of mammalian characters in the nasal capsule, brain and ear. However, these studies have focused on only a few taxa, the earliest of which is another Early Triassic cynodont, Thrinaxodon liorhinus. Galesaurus is phylogenetically stemward of Thrinaxodon and thus provides a useful test of whether the mammal-like features observed in Thrinaxodon were present even more basally in cynodont evolution. The cranial anatomy of G. planiceps is characterized by an intriguing mosaic of primitive and derived features within cynodonts. In contrast to the very similar internal nasal and braincase morphology of Galesaurus and Thrinaxodon, parts of the skull that seem to be fairly conservative in non-prozostrodont cynodonts, the morphology of the maxillary canal differs markedly between these taxa. Unusually, the maxillary canal of Galesaurus has relatively few ramifications, more similar to those of probainognathian cynodonts than that of Thrinaxodon. However, its caudal section is very short, a primitive feature shared with gorgonopsians and therocephalians. The otic labyrinth of Galesaurus is generally similar to that of Thrinaxodon, but differs in some notable features (e.g. proportional size of the anterior semicircular canal). An extremely large, protruding paraflocculus of the brain and a distinct medioventrally located notch on the anterior surface of the tabular, which forms the dorsal border of the large parafloccular lobe, are unique to Galesaurus among therapsids with reconstructed endocasts. These features may represent autapomorphies of Galesaurus, but additional sampling is needed at the base of Cynodontia to test this.
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Affiliation(s)
- Luisa C Pusch
- Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany.,Institut für Biologie, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Christian F Kammerer
- North Carolina Museum of Natural Sciences, Raleigh, NC, USA.,Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Jörg Fröbisch
- Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany.,Institut für Biologie, Humboldt-Universität zu Berlin, Berlin, Germany.,Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
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LeBlanc ARH, Brink KS, Whitney MR, Abdala F, Reisz RR. Dental ontogeny in extinct synapsids reveals a complex evolutionary history of the mammalian tooth attachment system. Proc Biol Sci 2018; 285:20181792. [PMID: 30404877 PMCID: PMC6235047 DOI: 10.1098/rspb.2018.1792] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Accepted: 10/12/2018] [Indexed: 12/23/2022] Open
Abstract
The mammalian dentition is uniquely characterized by a combination of precise occlusion, permanent adult teeth and a unique tooth attachment system. Unlike the ankylosed teeth in most reptiles, mammal teeth are supported by a ligamentous tissue that suspends each tooth in its socket, providing flexible and compliant tooth attachment that prolongs the life of each tooth and maintains occlusal relationships. Here we investigate dental ontogeny through histological examination of a wide range of extinct synapsid lineages to assess whether the ligamentous tooth attachment system is unique to mammals and to determine how it evolved. This study shows for the first time that the ligamentous tooth attachment system is not unique to crown mammals within Synapsida, having arisen in several non-mammalian therapsid clades as a result of neoteny and progenesis in dental ontogeny. Mammalian tooth attachment is here re-interpreted as a paedomorphic condition relative to the ancestral synapsid form of tooth attachment.
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Affiliation(s)
- Aaron R H LeBlanc
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6
- Department of Biological Sciences, Faculty of Science, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
| | - Kirstin S Brink
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6
- Department of Oral Health Sciences, Faculty of Dentistry, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada
| | - Megan R Whitney
- Department of Biology and Burke Museum, University of Washington, Seattle, WA, USA
| | - Fernando Abdala
- Unidad Ejecutora Lillo, Conicet, Tucumán, Argentina
- Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
- National Research Foundation, Centre of Excellence: Palaeosciences, Pretoria, South Africa
| | - Robert R Reisz
- Department of Biology, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6
- Institute of Oral Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan, Republic of China
- DERC, Jilin University, Changchun, Jilin Province, People's Republic of China
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Jasinoski SC, Abdala F. Aggregations and parental care in the Early Triassic basal cynodonts Galesaurus planiceps and Thrinaxodon liorhinus. PeerJ 2017; 5:e2875. [PMID: 28097072 PMCID: PMC5228509 DOI: 10.7717/peerj.2875] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 12/06/2016] [Indexed: 12/01/2022] Open
Abstract
Non-mammaliaform cynodonts gave rise to mammals but the reproductive biology of this extinct group is still poorly known. Two exceptional fossils of Galesaurus planiceps and Thrinaxodon liorhinus, consisting of juveniles closely associated with an adult, were briefly described more than 50 years ago as examples of parental care in non-mammaliaform cynodonts. However, these two Early Triassic fossils have largely been excluded from recent discussions of parental care in the fossil record. Here we re-analyse these fossils in the context of an extensive survey of other aggregations found in these two basal cynodont taxa. Our analysis revealed six other unequivocal cases of aggregations in Thrinaxodon, with examples of same-age aggregations among immature or adult individuals as well as mixed-age aggregations between subadult and adult individuals. In contrast, only one additional aggregation of Galesauruswas identified. Taking this comprehensive survey into account, the two previously described cases of parental care in Galesaurus and Thrinaxodon are substantiated. The juveniles are the smallest specimens known for each taxon, and the size difference between the adult and the two associated juveniles is the largest found for any of the aggregations. The juveniles of Thrinaxodon are approximately only 37% of the associated adult size; whereas in Galesaurus, the young are at least 60% of the associated adult size. In each case, the two juvenile individuals are similar in size, suggesting they were from the same clutch. Even though parental care was present in both Galesaurus and Thrinaxodon, intraspecific aggregations were much more common in Thrinaxodon, suggesting it regularly lived in aggregations consisting of both similar and different aged individuals.
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Affiliation(s)
- Sandra C Jasinoski
- Evolutionary Studies Institute, University of the Witwatersrand , Johannesburg , South Africa
| | - Fernando Abdala
- Evolutionary Studies Institute, University of the Witwatersrand , Johannesburg , South Africa
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Benoit J, Manger PR, Fernandez V, Rubidge BS. Cranial Bosses of Choerosaurus dejageri (Therapsida, Therocephalia): Earliest Evidence of Cranial Display Structures in Eutheriodonts. PLoS One 2016; 11:e0161457. [PMID: 27548428 PMCID: PMC4993441 DOI: 10.1371/journal.pone.0161457] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Accepted: 08/05/2016] [Indexed: 01/08/2023] Open
Abstract
Choerosaurus dejageri, a non-mammalian eutheriodont therapsid from the South African late Permian (~259 Ma), has conspicuous hemispheric cranial bosses on the maxilla and the mandible. These bosses, the earliest of this nature in a eutheriodont, potentially make C. dejageri a key species for understanding the evolutionary origins of sexually selective behaviours (intraspecific competition, ritualized sexual and intimidation displays) associated with cranial outgrowths at the root of the clade that eventually led to extant mammals. Comparison with the tapinocephalid dinocephalian Moschops capensis, a therapsid in which head butting is strongly supported, shows that the delicate structure of the cranial bosses and the gracile structure of the skull of Choerosaurus would be more suitable for display and low energy combat than vigorous head butting. Thus, despite the fact that Choerosaurus is represented by only one skull (which makes it impossible to address the question of sexual dimorphism), its cranial bosses are better interpreted as structures involved in intraspecific selection, i.e. low-energy fighting or display. Display structures, such as enlarged canines and cranial bosses, are widespread among basal therapsid clades and are also present in the putative basal therapsid Tetraceratops insignis. This suggests that sexual selection may have played a more important role in the distant origin and evolution of mammals earlier than previously thought. Sexual selection may explain the subsequent independent evolution of cranial outgrowths and pachyostosis in different therapsid lineages (Biarmosuchia, Dinocephalia, Gorgonopsia and Dicynodontia).
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Affiliation(s)
- Julien Benoit
- Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Braamfontein, 2050, Johannesburg, South Africa
- School of Anatomical Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
- * E-mail:
| | - Paul R. Manger
- School of Anatomical Sciences, University of the Witwatersrand, 7 York Road, Parktown, 2193, Johannesburg, South Africa
| | - Vincent Fernandez
- European Synchrotron Radiation Facility, 71 rue des Martyrs, 38000, Grenoble, France
| | - Bruce S. Rubidge
- Evolutionary Studies Institute (ESI), School of Geosciences, University of the Witwatersrand, Braamfontein, 2050, Johannesburg, South Africa
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