ANATOMICAL AND SYSTEMATIC STUDY OF PROXIMAL TARSALS OF UNGULATES FROM THE GESTE FORMATION (NORTHWESTERN ARGENTINA)

Over the last decades, Paleogene outcrops in northwestern Argentina have been yielding abundant information about the evolution of South American mammals during the early Cenozoic. This region was an important area of early diversification for several groups of native ungulates, particularly notoungulates, during the Eocene. Although many specimens were found in association with postcranial elements, most reports describe cranial material. It is well known that these postcranial elements can provide characters for phylogenetic analyses and important clues for paleobiological inferences. This study presents a series of postcranial remains (proximal tarsals) from the Geste Formation exposed in Antofagasta de la Sierra, Catamarca Province, Argentina. Three calcanei and two astragali are herein described, compared to those of extinct ungulates and taxonomically identified. A functional analysis allows inferring the association of these bones to different types of stances. One calcaneus is assigned to Toxodontidae (Notoungulata) and exhibits some plantigrade features. Presenting digitigrade-like morphology, the other two calcanei and an incomplete astragalus are assigned to Interatheriidae (Notoungulata). Another astragalus, characterized by a configuration suggesting a digitigrade posture, is assigned to Didolontidae Ernestokokenia cf. E. yirunhor. The study of the tarsal provides a more integrative view of the Paleogene forms of the region as well.