The Neotropical giant ground sloth Ocnotherium giganteum (Xenarthra: Mylodontinae) from the Late Pleistocene of Brazil: anatomy, palaeoneurology, and phylogenetic relationships

Xenarthrans are among the more iconic endemic groups of South American mammals. We present new specimens, including a nearly complete skull and two partial skeletons, of the giant mylodontid sloth Ocnotherium giganteum, a large quadrupedal herbivorous sloth from the Late Pleistocene of the intertropical region of Brazil. The comprehensive osteological description of O. giganteum provided here sheds light on a previously very poorly known member of the mammalian assemblage from the Pleistocene of the intertropical region of Brazil. For nearly 200 years the species was known from only three isolated teeth and has long been misunderstood. Although several features suggest affinities between O. giganteum and Lestodontinae, phylogenetic analysis places this species within Mylodontinae, and the taxon is characterized by 22 autapomorphies. Ocnotherium giganteum exhibits a distinctive dentition, featuring a first upper molariform that is strongly arched posteriorly, a long diastema between the second and third upper teeth, short and robust limbs with powerful muscles, a pentadactyl manus with three clawed digits, a pes with at least four digits, and dermal ossicles. Digital endocranial studies on Ocnotherium reveal that it was characterized by large olfactory bulbs, extensive cranial ­pneumatization, and a relatively small osseous labyrinth.