Among the great diversity of Oligocene mammals from Quebrada Fiera (Mendoza Province, Argentina), three families of typotherian notoungulates are very abundant. Since the first paper on archaeohyracids in 2010 until the last fieldwork in 2016, numerous unpublished remains were added to the collection. The study of all these remains, together with some revised materials, allows us to provide new anatomical data and some taxonomic decisions on these groups. Within Hegetotheriidae, we present one of the most complete skulls of “Prohegetotherium schiaffinoi” known to date, providing descriptions of certain previously unknown features of the caudal cranium; MCNAM-PV 3984 is discarded as belonging to Hegetotheriopsis sulcatus, as recently suggested, and is considered as Hegetotheriinae indet., like other isolated large specimens and some teeth previously determined as Prohegetotherium sp.; and several well-preserved specimens add to the sample of the pachyrukhine Prosotherium garzoni, including a partial maxilla with erupting P2. Concerning “Archaeohyracidae”, Archaeohyrax suniensis is now better represented, recording several ontogenetic stages previously observed in the Bolivian sample of this species. Finally, within Interatheriidae, most new dental material belongs to Argyrohyrax proavus, but an isolated upper molar suggests the presence of a different Interatheriinae at Quebrada Fiera, more similar to the Bolivian Brucemacfaddenia boliviensis than to other Deseadan (late Oligocene) taxa.

Key words: Mammalia, “Archaeohyracidae”, Hegetotheriidae, Interatheriidae, Agua de la Piedra Formation, Deseadan, Mendoza Province.

Santiago Hernández Del Pino [stgo86@gmail.com] and Esperanza Cerdeño [espe@mendoza-conicet.gob.ar], Paleobiología y Paleoecología, Instituto de Nivología, Glaciología y Ciencias Ambientales, Centro Científico Tecnológico- CONICET-Mendoza. Avda, Ruiz Leal s/n, 5500 Mendoza, Argentina. Federico D. Seoane [fseoane@gl.fcen.uba.ar], Universidad de Buenos Aires, CONICET, Instituto de Estudios Andinos Don Pablo Groeber (IDEAN), Facultad de Ciencias Exactas y Naturales, Ricardo Güiraldes 2160, C1428EGA Buenos Aires, Argentina.