Synchrotron and µCT scanning reveal a hitherto undescribed bone in the braincase of basal Cynodontia (Therapsida).

BENOIT, J; JASINOSKI, S. C.; FERNANDEZ, V; ABDALA, F.

Johannesburgo

Conferencia; 3rd National Conference on imaging with radiation (imgrad); 2017

Evolutionary Studies Institute

Cynosaurus, Galesaurus, and Thrinaxodon are among the basal most non-mammaliaform cynodonts (Cynodontia, Therapsida), and are therefore important for understanding the evolutionary origin of mammals. Detailed knowledge of their anatomy is critical for phylogenetic assessment and paleobiological reconstructions. Hence they are among the most thoroughly studied therapsids, especially the abundant Thrinaxodon, which has been researched using all possible techniques (e.g. serial sectioning, acid preparation, CT scanning, synchrotron scanning). Here, using µCT and synchrotron study of 51 non-mammaliaform therapsid skull, we report the presence of previously undescribed paired bones in the inter-orbital vacuity of the skulls in these basal Cynodontia. These bones contribute to the wall of the anterior part of the braincase and correspond to the orbitosphenoid. These findings demonstrates, the presence of a reduced but yet visible ossification of the anterior part of the braincase in these taxa, which fills a gap in our knowledge of the evolution of the orbitosphenoid in the root of the mammalian lineage. These findings also illustrates the importance of non-destructive µCT investigation prior to physical preparation and shows that even a well-known taxa like Thrinaxodon can still reveal new anatomical details using innovative imaging techniques.