On the revision of Octodontotherium: the oldest mylodontoid sloth

FRANÇOIS, PUJOS

Paris, Francia

Congreso; 8th International Congress of Vertebrate Morphology; 2007

Society of Vertebrate Morphology

    Oligocene sloths are not common. The Deseadan SALMA records the first appearance of mylodontid and megalonychid lineages. Octodontotherium, from the Deseadan of Patagonia, was first discussed by F. Ameghino at the end of XIXth century. The detailed description by R. Hoffstetter over 50 years ago is the last work on this genus, which is the only Oligocene sloth known from cranial and postcranial elements. A revision of the material assigned to Octodontotherium, collected by E. Riggs at the beginning of the XXth century and deposited in natural history museums in Chicago, Paris, La Plata, and Buenos Aires, allow the study of numerous postcranial elements (e.g. tibia and astragalus), as well as mandibles and a well-preserved skull. A preliminary revision of this material suggests the existence of a single species, O. grande Ameghino, 1895 (of which O. crassidens Ameghino, 1895 is a synonym). The discovery in Salla (Deseadan SALMA of Bolivia) of several remains closely related to Octodontotherium (probably a second smaller species) markedly increases the geographical distribution of the genus during the Deseadan SALMA. The recent discovery in late Miocene of the Peruvian Amazon of an M5 similar to O. grande suggests, in contrast with Hoffstetter’s opinion, that this lineage survived the Oligocene-Miocene transition. A phylogenetic analysis of Tardigrada, including Octodontotherium and based on cranial and postcranial characters, is in process and will test Gaudin’s (2004) hypothesis of mylodontine affinities of Octodontotherium.