CONICET | Buscador de Institutos y Recursos Humanos

Hegetotheriidae is one of the most advanced clades within the endemic South American placental Order Notoungulata. Thespecies Hegetotheriopsis sulcatus Kramarz & Paz, 2013 differs from all other known hegetotheriids in having a peculiarcombination of cranial and dental features, some of them shared with Archaeohyracidae (sister group of Hegetotheriidae).A previous cladistic analysis supported H. sulcatus as the earliest diverging hegetotheriid. Nevertheless, a more recentanalysis, based on a different data matrix, concluded that this species is an advanced form within the family, with the littleknownProhegetotherium sculptum Ameghino, 1897 (late Oligocene) being the most basal taxon. Here we present arevision of the concept and the content of P. sculptum based on a re-examination of the type specimens. We find that thismaterial exhibits several dental and cranial characters not recognized in all previous studies; we conclude that no specimenother than the types can be assigned to P. sculptum, and that all the synonymies previously proposed (i.e. P. shumwayi andP. crassus) are unfounded. A new cladistic analysis, combining characters from the two aforementioned analyses, confirmsthe position of H. sulcatus as the earliest diverging hegetotheriid. The taxon was originally described based on remainsfrom early Miocene deposits in central and northern Patagonia (Sarmiento, Chichinales and Cerro Bandera formations).Here we report new material from the late Oligocene of Cabeza Blanca (central Patagonia), and reassign other materialpreviously attributed to Prohegetotherium from presumably equivalent levels at Quebrada Fiera (central West Argentina).These remains extend the occurrence of H. sulcatus back to the late Oligocene, and fill an important gap of the early recordof Hegetotheriidae.