The Scelidotheriine Proscelidoxon (Xenartha: Mylododontidae) from the Late Miocene of Maimara (Northwestern Argentina)

PUJOS, F., CANDELA, A., GALLI, C., COIRA, B., REGUERO, M., DE LOS REYES, M., ABELLO, M.A.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2012 vol. 49 p. 668 - 674

0002-7014

Xenarthra constitutes one of the most peculiar clades of the South American mammalian fauna and includes sloths (Tardigrada), anteaters (Vermilingua), and armored xenarthrans (Cingulata). Its phylogenetic affinities among placental mammals and their origins remain doubtful (Asher andHelgen, 2010). Xenarthrans first appear in the Itaboraian age (late Paleocene?early Eocene; Oliveira and Goin, 2011) represented by the Dasypodidae in the locality of Itaboraí, Brazil. Sloths are first recorded from the early Oligocene (Tinguirirican age) of Chile and became abundant during the late Oligocene (Deseadan age), mainly in Argentina and Bolivia with representation of Mylodontidae and Megalonychidae (Pujos et al., 2012).The mylodontid clade is divided into two subfamilies: Mylodontinae and Scelidotheriinae following Gaudin (2004) and St-André et al. (2010). The Scelidotheriinae includes some of the most spectacular of the giant tardigrades, with several medium- to large-sized Quaternary forms. For example, Scelidotherium leptocephalum Owen, 1839, attained the size of a cow; it was a selective browser (Bargo et al., 2006a), capable of digging and excavated extensive burrows (Vizcaíno et al., 2001). These ground sloths were mainly characterized by an extremely specialized, elongated, and tubular skull, increasing number of lobes on the distal lower molariforms, pentadactyl manusand pes, flattened femur, and a concave cuboidal facet in the astragalus.Proscelidodon Bordas, 1935 appeared during the Huayquerian in Argentina and survived until the Chapadmalalan.The Quaternary witnessed the taxonomic diversification of the Scelidotheriinae, with four species belonging to the genera Scelidodon Ameghino, 1881, Catonyx Ameghino, 1891, and Scelidotherium Owen, 1840, which ranged across more than half of southern South America.Pre-Quaternary Scelidotheriinae are uncommon. The discovery of a nearly complete maxilla of Proscelidodon from the Maimará Formation (late Miocene), Jujuy Province (Fig. 1), provides new data on the plesiomorphic condition of the clade, the biogeographic history of the group during theMio?Pliocene, and on the Maimará faunal assemblage.