Digital endocranial reconstructions of the extinct scelidothere sloths (Xenarthra, Mylodontidae): emerging patterns in folivorans? evolution

BOSCAINI, ALBERTO; IURINO, DAWID A.; CARTELLE, CÁSTOR; STRAUSS, ANDRÉ; DE IULIIS, GERARDO; SARDELLA, RAFFAELE; TIRAO, GERMAN; GAUDIN, TIMOTHY J.; PUJOS, FRANÇOIS

Paris

Congreso; 5th International Palaeontological Congress; 2018

The latest CT-scanning facilities and 3D imagery techniques are greatly improving our understanding of animal morphology, revealing important aspects of the internal cranial anatomy for both extant and extinct vertebrates. This non-destructive methodology has the potential to greatly facilitate studies of adaptations and paleobiology for fossil species. Recent research on the extinct giant mylodontine sloth Glossotherium robustum allowed the documentation of many previously unknown structures, such as the inner ear, brain cavity, paranasal sinuses, and trajectory of several cranial nerves and blood vessels. It was also possible to compare these structures with their counterparts in the living arboreal sloth gen-era Bradypus and Choloepus, together with the extant anteaters and armoured cingulates. Their morphologies suggest the influence of different effects, such as phylogenetic imprint, as well as allometric and functional components, and reveal the importance of the application of these techniques for elucidating the evolutionary history of sloths. For this reason, we extended our observations, performing new CT scans on some representatives of another highly peculiar group of mylodontid sloths, the Scelidotheriinae. This new sampling includes several South American Pliocene and Pleistocene taxa that are not necessarily closely related phylogenetically. It includes small-and large-sized forms, and individuals of various ontogenetic stages, in order to encompass the different morphologies, respectively related with phylogeny, allometry, and ontogeny. Preliminary qualitative data reveal a conservative morphology of the brain casts (i.e., olfactory bulbs, cerebral hemispheres, and cerebellum) among Mylodontidae, despite their marked differences in their external cranial anatomy. On the contrary, paranasal sinuses show marked differences between Scelidotheriinae and Mylodontinae, in both shape and size. The observed morphology of the paranasal pneumatization seems to be affected also by ontogenetic development, and to be less related with allometry than previously expected. The current study represents the first exploration of the endocranial morphology of the scelidotheriine sloths through digitally-based methods, and a further step toward the comprehension of sloth anatomy and evolution.