A new turtle from the P alaeogene of P atagonia ( A rgentina) sheds new light on the diversity and evolution of the bizarre clade of horned turtles ( M eiolaniidae, T estudinata)

In this contribution we present a new species of horned turtle, Gaffneylania auricularis gen. et sp. nov. , from the P aleogene of P atagonia. The specimens come from the lower section of the S armiento F ormation ( M iddle E ocene) at C erro V erde ( C añadón H ondo area, P rovince of C hubut, A rgentina). 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 C asamayoran SALMA . G affneylania auricularis represents one of the most complete meiolaniids from S outh A merica 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 M eiolaniidae in A ustralasia and S outh A merica during the C ainozoic. The break up of southern G ondwana provoked major global climatic changes during the C ainozoic 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. © 2015 The Linnean Society of London