Synopsis of the fossil freshwater crabs of Europe (Brachyura: Potamoidea: Potamidae)

The reappraisal of the European Neogene fossil freshwater crabs results in the recognition of eight species, including one new species (Potamon hegauense n. sp.) of late Miocene age (c. 10.3 Ma) from Howenegg (southern Germany). All eight species are assigned to the genus Potamon (Potamidae). There is no morphological evidence for a closer relationship with African potamonautids. The oldest known European freshwater crab is Potamon quenstedti from Engelswies (early Miocene, c. 17 Ma) in southern Germany. The last occurrence of potamids in Central Europe prior to the Pleistocene is recorded in the Vienna Basin (late Miocene, c. 8 Ma). In Italy (Tuscany) freshwater crabs (Potamon castellinense) are documented well before (c. 5.5 Ma) the presumed postglacial invasion of extant Potamon fluviatile. The latest Pliocene-Pleistocene species Potamon antiquum from northern Hungary probably represents extinct populations of Potamon ibericum at the northern limit of its range. The scarce records and the lack of dating of the southwest Asian Potamon sivalense hampers considerations about origin, dispersal events and palaeobiogeography of potamids in Europe up to now. However, a slow southward withdrawal of freshwater crabs, induced by climate cooling at the end of the Miocene, is marked by the extinction of P. hegauense in the circum-Alpine realm, P. antiquum in Hungary, and probably P. castellinense in Italy.