New metatherians from Collon Cura Formation at Cerro Zeballos (Middle Miocene), Chubut province, Argentina

Abstract

High latitude metatherians from the Middle Miocene of Patagonia (Argentina and Chile) are only known from medium-sized Sparassodonta, and undescribed taxa collected in several fossil localities of Collon Cura (Argentina) and Río Frías (Chile) Formations, although the latter has several species reported and mostly recognised for the slightly older Santa Cruz Formation. In this contribution we describe five new genera and six new species of metatherians from Collon Cura Formation at Cerro Zeballos, Chubut province (Argentina), based on 11 specimens that notably increased the diversity of Collon Cura Formation. The specimens were assigned to the orders Paucituberculata (Palaeothentoidea), Sparassodonta (Hathliacynidae), and Polydolopimorphia (Argyrolagidae), and are taxa of small size, including the smallest palaeothentoids known to date. Also, the Palaeothentoidea of Cerro Zeballos are amongst the youngest of the superfamily in Patagonia. The new specimens described herein show morphological differences with other metatherian associations already known, probably related to adaptive changes coincident with the Middle Miocene Climatic Transition and the beginning of a faunal turnover.