Past, present, and future of southern Gondwanan turtles: a view from the South

Extinct turtles from southern Gondwana are known from the 19th century. However, two-thirds of their knowledge has been produced during the last 30 years, changing notably our understanding of the evolution of the cheloniofauna of this region. Nowadays, there are more than 600 occurrences of turtles in southern Gondwana spanning from the Lower Jurassic until the Holocene. The aim of this work is to provide an updated account of the diversity and distribution of southern Gondwanan turtles and to test whether it is possible to recognize the three phases of evolution of continental turtles suggested for South America. We also compared the paleolatitudinal distribution of turtles between hemispheres, especially in temperate regions, showing that the fossil record is heavily skewed towards the north. The recent efforts have improved the southern Gondwanan fossil record, allowing for more complete diversity curves with evidence of a K/Pg extinction, but still, an important part of the past diversity is missing. In southern Gondwana, like in South America, the first two phases in the evolution of continental turtles, the Pangean and the Gondwanan, can be recognized in a similar fashion. However, the final part of the evolution of turtles in southern Gondwana differs in Patagonia and Australia + Zelandia because they have undergone different biogeographic histories. In Patagonia, chelids and meiolaniids became extinct after the middle Eocene, and it was not until the late Oligocene that tortoises arrived in South America, and that turtles roamed again in that region. On the contrary, in Australia, chelids and meiolaniids diversified during the Neogene, reaching distant islands in the case of meiolaniids. The Neogene-Recent Australian cheloniofauna is completed by the arrival of trionychids and carettochelyids from Asia.