Microcomputed tomography analysis of the basicranial axis of emydopoid dicynodonts and an investigation of their adaptations to fossorial behaviour

Macungo, Zanildo Augusto
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Emydopoidea form one of the few clades among dicynodonts that contains fossorial species, although their basicranial adaptations to this lifestyle have been poorly studied. Various cranial and postcranial anatomical features specialized for fossoriality have been identified for a long time in cistecephalid emydopoids. Here, using X-ray micro-computed and synchrotron tomography, I provide detailed anatomical descriptions of the basicranial axis of three emydopoids, Myosaurus, Kawingasaurus, and a Malawian cistecephalid (PK-16-1), and compare them to the basal dicynodont Pristerodon. Notable features include the presence of divergent crests on the posterior aspect of the opisthotic and a nuchal crest on the occipital plate of various emydopoids, particularly cistecephalids, which contrasts with the relative featureless occipital plate of other dicynodonts (with the exception of Myosaurus). These depressions and crests increase the muscular attachment area for the atlantooccipital and may represent an adaptation to head-digging in cistecephalids, analogous to some extant fossorial taxa. Kawingasaurus has a highly derived basicranium, with a vast network of trabecular spaces and highly coossified basicranium, which is probably linked to the auditory system. I propose that cistecephalids, in addition to being forelimb-diggers, were likely head-diggers, and highlight some derived adaptations consistent with a quasi-obligate fossorial lifestyle. I also propose new basicranial phylogenetic characters and, reevaluate the intra-and interrelationships among emydopoids accordingly. My analysis recovers Rastodon as a basal emydopoid, Thliptosaurus as a non-kingoriid emydopoid, and Sauroscaptor, Kembawacela and the new Malawian cistecephalid PK-16-1 forming a polytomy among cistecephalids
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science, 2021