Comparative anatomy of intracranial osseous canals and alveolar cavities provide further clues on the relationships between glyptodonts and armadillos (Xenarthra, Cingulata)

LE VERGER, KÉVIN; GONZÁLEZ RUIZ, L.R.; BILLET, GUILLAUME

Otro; 81st Annual Meeting of the Society of Vertebrate Paleontology; 2021

The evolutionary history of the Cingulata, as for many groups, remains a highly debated topic to this day, particularly for one of their most emblematic representatives: the glyptodonts. There is currently no consensus among morphological and molecular phylogenies relative to their position within Cingulata. Recent works have shown that the study of the internal cranial anatomy constitutes a promising path for enriching morphological matrices for the phylogenetic study of armadillos, but it remains under-studied in the Cingulata. Here we explored and compared the anatomy of intracranial osseous canals and cavities in a diverse sample of extant and extinct cingulates consisting of nine extant genera and 11 fossil species including one representative of Pleistocene glyptodonts and four earliest (i.e., early Miocene) well-preserved glyptodont crania. X-ray microtomography, we virtually reconstructed in 3D the following selected canals and cavities: the nasolacrimal canal, the palatine canal, the sphenopalatine canal, the canal for the frontal diploic vein, the transverse canal, the orbitotemporal canal, the canal for the capsuloparietal emissary vein and the posttemporal canal, and alveolar cavities related to cranial vascularization, innervation or tooth insertion. Comparison of the locations, trajectories and shape of these structures allowed us to provide a wealth of new anatomical data, to discuss their potential interest for cingulate systematics, and to reconstruct evolutionary scenarios for eight selected traits on these structures.For these traits, glyptodonts generally showed a greater resemblance to pampatheres, to the eutatine genus Proeutatus and/or to chlamyphorines. For instance, we demonstrate that the position of the most dorsal point of the dorsal convexity of the tooth row and the sphenopalatine and palatine canal connection exhibit similarities between dwarf and giant armadillos. Resemblance to the latter is partly congruent with recent molecular hypotheses and would thus support a close relationship between these dwarf and giant forms among cingulates. Overall, this research highlights the systematic interest in the study of endocranial canals and alveolar cavities, which remain poorly studied in mammals, especially for fossil taxa.