Postcranial anatomy of the extinct terrestrial sloth Simomylodon uccasamamensis (Xenarthra, Mylodontidae) from the Pliocene of the Bolivian Altiplano, and its evolutionary implications

Abstract

Extinct terrestrial sloths are common elements of the late Cenozoic South American fossil record. Among them, Mylodontinae species were particularly abundant in the Americas throughout the Pleistocene epoch, and their anatomy is relatively well known. In contrast, less information is available from the Neogene record and particularly from localities at low latitudes, with an additional and considerable bias in favour of craniodental rather than postcranial remains. In this contribution, we provide comparative descriptions of several postcranial bony elements ascribed to Simomylodon uccasamamensis, a moderate-sized extinct mylodontine from the Andean Altiplano. This species was particularly abundant during latest Miocene – late Pliocene times in the high altitudes of the Andean Cordillera, and so far represents the best known mylodontine from the Neogene of South America. Its anatomy is compared with that of several extinct terrestrial sloths, with the aim of using the observed morphologies to elucidate taxonomy, phylogeny, and locomotion. From a morphofunctional perspective, the postcranium of S. uccasamamensis is consistent with that of a terrestrial graviportal quadruped, with moderate climbing and digging capabilities.