A new turtle from the Palaeogene of Patagonia (Argentina) sheds new light on the diversity and evolution of the bizarre clade of horned turtles (Meiolaniidae, Testudinata)

In this contribution we present a new species of horned turtle, Gaffneylania auricularis gen. et sp. nov., from the Paleogene of Patagonia. The specimens come from the lower section of the Sarmiento Formation (Middle Eocene) at Cerro Verde (Canadon Hondo area, Province of Chubut, Argentina). The level containing turtles and crocodyliforrmes is located at the base of the section and it consists of laminated, fine tuffs interpreted as shallow pond sediments. It underlies another fossiliferous level comprising lenticular, massive sandstones bearing skeletal remains of mammals, referred by previous authors to the Casamayoran SALMA. Gaffneylania auricularis represents one of the most complete meiolaniids from South America found to date and it is distinguished from other meiolaniids by the presence of a peculiar half-moon-shaped, thick rim surrounding the cavum tympani, the presence of three cranial scutes K and an unenclosed canalis chorda tympani mandibularis, among others. This new species sheds new light on the evolution and palaeobiogeographical history of the clade Meiolaniidae in Australasia and South America during the Cainozoic. The break up of southern Gondwana provoked major global climatic changes during the Cainozoic that probably influenced the evolution of meiolaniid turtles. The co-evolution of meiolaniids with other amniotes (e.g. chelid turtles, mammals) suggests a common palaeobiogeographical history of those clades in southern Gondwana. (C) 2015 The Linnean Society of London.