CONICET | Buscador de Institutos y Recursos Humanos

In the last decades, Paleogene outcrops in northwestern Argentina have provided abundant information about the evolution of South American mammals during the early Cenozoic. This region constituted an important area of early diversification for several groups of native ungulates during the Eocene, especially notoungulates. To date, most reports describe cranial material, even when in many cases specimens are found in association with postcranial elements. It is well known that these elements can provide characters for phylogenetic analyses and supply important clues for paleobiological inferences. This study presents a series of postcranial remains (proximal tarsals) from the Geste Formation, which crops out at Antofagasta de la Sierra, Catamarca Province,Argentina. Three calcanei and two astragali are described, compared with those ofextinct ungulates, and systematically determined. A functional analysis allows inferring the association of these bones with different types of stances. One calcaneus is assigned to Toxodontidae (Notoungulata) and exhibits some plantigrade features. The other two calcanei and an incomplete astragalus are referred to Interatheriidae (Notoungulata), showing digitigrade-like morphology. Another astragalus is referred to Didolontidae Ernestokokenia cf. yirunhor?; its configuration suggesting a digitigrade posture. The study of the tarsal provides, as well, a more integrative view of the Paleogene forms of the region.