Evaluating the origin of Cynodontia (Synapsida, Therapsida) using 3D-Imaging Technologies

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Cynodontia is the most abundant and diverse group of synapsids, as it includes mammals, which evolved from non-mammalian cynodonts in the Late Triassic. The evolution of mammals from cynodonts is one of the best-understood and well-studied major transitions in the fossil record. In contrast, the origin of cynodonts themselves from other synapsids is very poorly known. It is well-established that cynodonts are most closely related to Therocephalia, but it is not clear whether cynodonts and therocephalians are sister-taxa or whether therocephalians are paraphyletic with regards to cynodonts. Also uncertainties exist concerning the phylogenetic relationships of the earliest member of this clade. By contrast, the relationships of higher cynodonts (eucynodonts) are well understood. The main objectives of the proposed project are a re-evaluation of the relationships of Eutheriodontia (Cynodontia+Therocephalia) and an assessment of character evolution within the group based on new CT data, i.e. detailed descriptions of the endocranial anatomy of the earliest known (late Permian and Early Triassic) cynodonts and selected therocephalian relatives. Modern 3D-imaging technologies using computed tomography can make previously-unseen endocranial data readily available, which are a largely untapped resource for understanding therapsid evolution, despite their greater stability and phylogenetic utility than many functionally-variable external craniodental characters. The primary hypothesis to be tested using these data is whether Cynodontia and Therocephalia are sister-taxa or whether cynodonts evolved from within Therocephalia. Furthermore, the novel insights into the endocranial anatomy are useful to test if the origin of characteristic mammalian but also cynodont characters can be traced back deeper in eutheriodont phylogeny and allow, at the same time, to investigate the deep-time evolution of delicate endocranial structures, such as the epipterygoid or alisphenoid elements. Finally, in addition to testing questions of cynodont origins, the new data will also help to resolve the currently unstable intra- and interrelationships among early cynodonts and therocephalians using modern phylogenetic approaches.