Morphological and histological characterization of the osteoderms of Priodontes maximus and Cabassous tatouay (Xenarthra, Tolypeutinae)

BARASOAIN, DANIEL; LUNA, CARLOS; ZARACHO, ELBA M.; SUPERINA, MARIELLA

Congreso; XXXIII Jornadas Argentinas de Mastozoología; 2022

The Tolypeutinae Priodontes maximus (Kerr, 1792) and Cabassous tatouay (Desmarest, 1804) are among the most fossorial armadillos. According to molecular data, Tolypeutinae is one of the latest lineages of armadillos to diverge (ca. 25 Ma.), which is consistent with morphologicalphylogenetic analyses including extinct and extant taxa. In this framework, we performed a morphological and histological analysis of the osteoderms of the dorsal carapace of P. maximus and C. tatouay. Contrary to expected given the late divergence of Tolypeutinae, both show a highly plesiomorphic external morphology of the osteoderms, including a very rough dorsal surface and alack of ornamentation pattern in the bony surface (while it is preserved in the horny scales covering the osteoderms). Histologically, the osteoderms of these taxa present major differences. Cabassous osteoderms are similar to most extant armadillos, including a diploe-like structure,with cancellous bone occupying one third of the osteoderms’ thickness. In turn, Priodontes has mainly compact osteoderms with few resorption spaces, being in some aspects (i.e., presence of thick bundles of structural fibers reinforcing these dermal structures) more similar to theosteoderms of the extinct Glyptodontidae and Pampatheriidae. These plesiomorphic characters are restricted to the dorsal carapace, and not observed in early-divergent tolypeutines such as the Miocene genus Vetelia (Ameghino, 1891). Interestingly, a similar process has beenobserved in the Chlamyphorinae (fairy armadillos) whose modern representatives manifest more plesiomorphic osteoderm morphologies than their Miocene relatives. In this context, this “phenotypic regression” would have simultaneously occurred in the carapace of two distinctlineages. These changes may be related to a progressive adaptation to a more fossorial life habit from the Miocene to the present. Additionally, given that the mainly insectivorous diet of both C. tatouay and P. maximus implies a low energy intake, developing less complex osteodermsmay represent an important energy saving.