A unique snake assemblage from the Early Miocene locality of Wintershof-West, Germany, with comments on the transitional period in the evolution of European snake fauna

Abstract The early Burdigalian (20.4–18.2 Ma) ophidian localities are rare in the European fossil record and with exception of Merkur-North (Ahníkov I), Czechia (early MN 3) our knowledge on the evolution of snake communities before the Early Ottnangian Cooling (EOC; 18.1–17.8 Ma) event are still strongly restricted. Here we present the unusually diversified snake community from the German Early Miocene (early Burdigalian, early MN 3) Wintershof-West locality based on the detailed comparative osteological studies with a special focus on the intracolumnar variability. The following snake taxa have been reported from Wintershof-West: Alethinophidia incertae sedis (cf. Falseryx sp.), Booidea ( Bavarioboa wintershofensis sp. nov., Booidea indet.), Viperidae (Viperinae indet. – ‘Oriental vipers’, Vipera sp. [ ‘V. aspis’ complex]), Elapidae ( ‘Micrurus’ gallicus , Elapidae indet., type 1), Natricidae ( Natrix cf. sansaniensis , Wintershofia robusta gen. et sp. nov., Palaeonatrix aff. lehmani , Natricidae indet., type 1, Natricidae indet.), ‘Colubridae’ ( ‘Coluber’ aff. caspioides , ‘Colubridae’ indet., type 1, 2, and 3, ‘Colubridae’ indet.), and Colubroidea indet. The snake community from Wintershof-West documents the first return of the genus Bavarioboa ( B. wintershofensis sp. nov.) into Europe after its temporal demise from European region during the latest Oligocene climatic deterioration. Colubriform snakes became diversified in Central Europe during the onset of the early Burdigalian ~20 Mya. Viperid snakes from Wintershof-West comprise the earliest known distinct appearance of ‘Oriental vipers’. Several other colubriform taxa display their first documented appearance including Palaeonatrix aff. lehmani and ‘Coluber’ aff. caspioides which might represent the evolutionary older members of the ‘C.’ caspioides and P. lehmani lineages. The unusual diversification of snake taxa resulted from the onset of the warm early Burdigalian climate, which we refer here as the Eggenburgian Climatic Optimum (ECO). The presence of several thermophilic taxa in Wintershof-West including cf. Falseryx sp., Bavarioboa wintershofensis sp. nov., ‘Micrurus’ gallicus and another indeterminate coral snake, and ‘Oriental vipers’, point to a relatively major warming before the onset of the EOC event. However, the absence of highly thermophilic true cobras of the genus Naja as well as Pythonoidea in Central European MN 3 localities demonstrates mean annual temperatures did not reach their maximum, as during the Miocene Thermal Maximum (MTM, MN 4) of the middle and late Ottnangian. The karstic environment around the Wintershof-West locality corresponds to the semi-arid hydroclimate which fits with the numerous small booidea and ‘Oriental vipers’. Wintershof-West is the best documented early Burdigalian (early MN 3, Eggenburgian) ophidian locality in Europe which substantially increases our knowledge of the evolution of European snake fauna during its transitional period of the early Burdigalian.