Taxonomic revision and phylogeny ofPaedotheriumandTremacyllus(Pachyrukhinae, Hegetotheriidae, Notoungulata) from the Late Miocene to the Pleistocene of Argentina

Two genera of the subfamily Pachyrukhinae (Notoungulata, Hegetotheriidae), Paedotherium and Tremacyllus, are revised. The material comes from late Miocene (Chasicoan) to early Pleistocene (Marplatan) localities in Argentina and Bolivia. The genus Raulringueletia is here considered a synonym of Paedotherium. Three valid species of Paedotherium are recognized and re-characterized: P. bonaerense, P. typicum, and P. minor. Two species of Tremacyllus are recognized: T. impressus in the Pampean region, and T. incipiens in Catamarca Province. The presence of Tremacyllus sp. into the late Chasicoan extends its known temporal range. Pachyrukhos occurs slightly earlier within the Chasicoan, coexisting with Paedotherium. Paedotherium is dominant in frequency in the Pampean area (Buenos Aires and La Pampa) and extremely scarce in the Subandean region (Catamarca), while Tremacyllus has an opposite occurrence. Cladistic analysis of the subfamily shows Paedotherium as a monophyletic group, where P. bonaerense is the sister taxon of the clade P. minor plus P. typicum. Pachyrukhos is the sister group of Paedotherium, and Tremacyllus appears to be closer to Pachyrukhos or Propachyrucos than to Paedotherium.