Evolution of anuran assemblages in the Tertiary and Quaternary of Europe, in the context of palaeoclimate and palaeogeography
The history of the faunas of anurans during the Tertiary and Quaternary in Europe is presented. Two families (Discoglossidae and Palaeobatrachidae) were recorded from the Cretaceous of Europe and both survived the Cretaceous/Tertiary crisis. The earliest known Tertiary anurans, represented by the Discoglossidae and perhaps Palaeobatrachidae, come from Hainin, Belgium (middle Paleocene). Only the Bufonidae appear to join them before the end of the Paleocene, however, they subsequently disappeared only to re-appear at the beginning of the Miocene. The paucity of Paleocene data is due to a lack of fossiliferous strata, rather than a post-Cretaceous discontinuity of the anuran fauna. Europe and North America were separated by the Atlantic Ocean in the early Eocene (50 Ma) and climate at that time was tropical. Ranidae, Pelobatidae, Pelodytidae, Leptodactylidae appeared in the Eocene; the last family was represented by the genus Thaumastosaurus which is a Gondwanan element. Others were either immigrants, probably from Asia, or originated in Europe (Pelodytidae) or in North America (Pelobatidae). Supposed temporary presence of the Microhylidae and Rhacophoridae in the European Eocene requires further confirmation. A drop of temperature at the end of the Eocene (one of the causes of a crisis called the 'Grande Coupure') is associated with the definitive disappearance of the Leptodactylidae in Europe and of palaeobatrachids from the region of the British Isles, as well as the temporary disappearance of the pelodytids (until they re-appear in the Miocene). During the Oligocene, the European anuran fauna was comparatively stable, only forms belonging to the group of green frogs (Ranidae) appeared in the early Oligocene. In the early Miocene, the Hylidae appeared, whereas the Pelodytidae and Bufonidae re-appeared. The most diversified anuran fauna in the history of Europe was in early Miocene (approx. 20 Ma) when some extant genera and even species first appeared. Since then, the diversity of the European anuran assemblages decreased, mainly as a result of climatic deterioration. During the early Pleistocene, the discoglossid genus Latonia and the entire family Palaeobatrachidae became extinct, undoubtedly because of continental glaciation.