The Xenarthra (Mammalia) of São José de Itaboraí Basin (upper Paleocene, Itaboraian), Rio de Janeiro, Brazil

Here we present new information on the oldest Xenarthra remains. We conducted a comparative morphological analysis of the osteoderms and postcranial bones from the Itaboraian (upper Paleocene) of Brazil. Several osteoderms and isolated humeri, astragali, and an ulna, belonging to at least two species, compose the assemblage. The bone osteoderms were assigned to Riostegotherium yanei Oliveira & Bergqvist, 1998, for which a revised diagnosis is presented. The appendicular bones share features with some “edentate” taxa. Many of these characters may be ambiguous, however, and comparison with early Tertiary Palaeanodonta reveals several detailed, derived resemblances in limb anatomy. This suggests that in appendicular morphology, one of the Itaboraí Xenarthra may be the sister-taxon or part of the ancestral stock of Palaeanodonta.