Beurteilung des Ursprungs der Cynodontia (Synapsida, Therapsida) mit Hilfe von 3D-Bildtechnologien
Zusammenfassung der Projektergebnisse
Computed tomography (CT) is a non-destructive imaging technique that has been widely used on fossil vertebrate crania in recent years and allowed paleontologists to investigate previously-obscure endocranial data. The latter have been instrumental in elucidating patterns of inner ear and brain evolution, facial innervation, tooth replacement and the origin of endothermy along the mammalian stem lineage (Synapsida). Although endocranial characters have been described for various synapsids in recent years, they remain understudied compared to the well-known external craniodental features in synapsids and have been largely ignored in phylogenetic analyses. In this project we provided a re-evaluation of the phylogeny of Eutheriodontia (the synapsid subclade consisting of Cynodontia+Therocephalia) and an assessment of character evolution within the group. The origin of cynodonts, the group ancestral to (and including) mammals, is one of the major outstanding problems in therapsid evolution. It is well-established that cynodonts are most closely related to Therocephalia among the major synapsid groups, but the exact nature of this relationship was uncertain. Furthermore, although a fundamental dichotomy in the derived Triassic subclade Eucynodontia is well-supported in cynodont phylogeny, the relationships of more stemward cynodonts are currently unresolved. Using CT 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 (eucynodonts), we described novel aspects of the endocranial anatomy of these animals. These data were incorporated into a new, taxonomically comprehensive phylogenetic dataset of the group, providing new information on endocranial variation and the assembly of mammalian characters in eutheriodont evolution. Furthermore, the new CT data obtained from investigating the endocranial anatomy of the earliest known cynodont taxa could be integrated with the already well understood data from crownward cynodonts for a more holistic view of the early evolution of the clade. The results of our phylogenetic analyses support some relationships 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. The combination of homoplasy and conservatism in various parts of the endocranium of early cynodonts though is shown to limit the utility of endocranial characters for resolving lower-level relationships in this grade. Nevertheless, our inclusion of these characters did result in a better resolved phylogeny of early cynodonts compared to what has been recovered in Pusch et al. (2021) and (2023), and previous phylogenetic analyses using almost exclusively external craniomandibular characters. Furthermore, there are clear trends in endocranial character evolution at higher taxonomic levels (such as between therocephalians and cynodonts and between early and later cynodonts), suggesting considerable utility in these characters for resolving the phylogeny of synapsid groups more broadly (e.g., in resolving the contentious relationships of the major therapsid clades). This is clearly indicated based on our results, in which we recovered the therocephalian paraphyly with strong support in the performed analyses. Thus, we can clearly refute our first hypothesis that Cynodontia and Therocephalia are reciprocally-monophyletic clades in a sister-taxon relationship. As such, we still strongly support additional sampling and adding endocranial characters to future analyses of synapsid evolution. Even where homoplasy complicates phylogenetic analysis, it is telling us important information on the evolutionary history of the group, with potential functional implications for morphologies that evolved multiple times in therapsid evolution. All in all, this project presents novel data in particular on the endocranial anatomy of early eutheriodonts, as well as their intra- and interrelationships and character evolution within the clade, leading to new advances in our understanding of the origin of cynodonts. Our results support some and refute others from our initial hypotheses and lay the groundwork for future macroevolutionary studies surrounding the origin of Cynodontia (including mammals).
Projektbezogene Publikationen (Auswahl)
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Cranial anatomy of the early cynodont Galesaurus planiceps and the origin of mammalian endocranial characters. 12th International Congress of Vertebrate Morphology (ICVM), Prague, Czech Republic.
Pusch, L.C., Kammerer, C.F. & Fröbisch, J.
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Revisiting the Cranial Anatomy of Lycosuchus vanderrieti (Therapsida: Therocephalia) from the middle Permian of South Africa, based on CT-reconstruction. 12th International Congress of Vertebrate Morphology (ICVM), Prague, Czech Republic.
Ponstein, J., Pusch L.C., Kammerer, C.F. & Fröbisch, J.
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Novel Endocranial Data on the Early Therocephalian Lycosuchus vanderrieti Underpin High Character Variability in Early Theriodont Evolution. Frontiers in Ecology and Evolution, 7.
Pusch, Luisa C.; Ponstein, Jasper; Kammerer, Christian F. & Fröbisch, Jörg
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Cranial anatomy of Bolotridon frerensis , an enigmatic cynodont from the Middle Triassic of South Africa, and its phylogenetic significance. PeerJ, 9, e11542.
Pusch, Luisa C.; Kammerer, Christian F. & Fröbisch, Jörg
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Cranial anatomy of Nythosaurus larvatus Owen, 1876, an Early Triassic cynodont preserving a natural endocast. Journal of Vertebrate Paleontology, 42(3).
Pusch, Luisa C.; Kammerer, Christian F.; Fernandez, Vincent & Fröbisch, Jörg
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Craniomandibular anatomy of the akidnognathid therocephalian Olivierosuchus parringtoni from the Early Triassic Karoo Basin of South Africa. Palaeontologia africana 56:142–170.
Gigliotti, A., Pusch, L. C., Kammerer, C. F., Benoit, J. & Fröbisch, J.
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Redescription of the of the holotype of Olivierosuchus parringtoni (BP/1/3849). 94. Jahrestagung Paläontologische Gesellschaft, Jena, Deutschland.
Gigliotti, A., Pusch, L.C., Kammerer, C.F., Benoit, J. & Fröbisch, J.
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Endocranial anatomy of Olivierosuchus parringtoni (Synapsida, Therocephalia). 21th European Association of Vertebrate Palaeontologists (EAVP), Longyearbyen, Svalbard, Norway.
Gigliotti, A., Pusch, L.C., Kammerer, C.F., Benoit, J. & Fröbisch, J.
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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. The Anatomical Record, 307(4), 1634-1730.
Pusch, Luisa C.; Kammerer, Christian F. & Fröbisch, Jörg
