Oligocene to Pleistocene mudwhelks (Gastropoda: Potamididae, Batillariidae) of the Eurasian Paratethys Sea - Diversity, origins and mangroves

Potamidids (Potamididae, Batillariidae) are today typical inhabitants of coastal mudflats in tropical and warm temperate seas. From the Oligocene to the Early Pleistocene, the Eurasian Paratethys Sea harbored a striking diversity of mudwhelks as well. Based on occurrences from 466 localities covering an area of about 3 million km2 we trace range expansions of potamidids from the Western Tethys and the Proto-Mediterranean Sea into the Eurasian Paratethys Sea, coinciding with global warming trends, such as the Miocene Climate Optimum, the Tortonian Thermal Maximum and the Mid-Pliocene Warm Period. For several species and genera, the stratigraphically oldest occurrences are documented from Rupelian localities south of the Paratethys, which indicates a northward migration over time. A hypothetical refuge along western Africa is hypothesized to explain the 9 Myr long gap between Oligocene and Sarmatian occurrences of Potamides in Europe. Highest potamidid diversities in the Central Paratethys coincided with the Miocene Climate Optimum. The second diversity peak is observed during the Sarmatian when the Volhynian flooding united the Central and Eastern Paratethys in a "Mega-Paratethys". This event appears to have boosted potamidid diversity at least in the western part of the Paratethyan basin. About 25% of the species belong to Paratethyan lineages, which partly passed the Badenian/ Sarmatian Extinction Event.A close relation with mangrove environments is documented for Mesohalina, Ptychopotamides and Terebralia and is assumed for Tiarapirenella. The retreat of mangroves from the Paratethys following the Miocene Climate Optimum is reflected by the loss of large species. Latest Middle Miocene to Late Miocene (Sarmatian) potamidid faunas were dominated by species of Tiaracerithium and Potamides, which were adapted to mudflats devoid of mangroves. Maeotian and Akchagylian potamidid faunas were low diverse, comparatively small and indicate two last phases of immigrations from the Mediterranean region. An influx from the Arctic region during the "Akchagylian marine incursion" can be excluded as explanation for the exotic occurrence of Akchagylian potamidids.