The Early-Middle Miocene freshwater mollusk fauna of the Mecsek Mts. (S Hungary): a biogeographic stepping stone

The Mecsek Mts. in southern Hungary were fringed by a freshwater paleolake during the late Early–early Middle Miocene. Its position just north of the Dinarides places the lake at the biogeographic crossroads between the highly endemic faunas of the Dinaride Lake System and the more widely distributed freshwater systems scattered around the Central Paratethys. However, only few species have been identified from the deposits so far, complicating an in-depth assessment of biogeographic affinities. Here, we provide a thorough taxonomic assessment of the fauna based on new material from freshwater deposits exposed at six localities, primarily at the southeastern margin of the Mecsek Mts. We expand the species inventory to a total of 17 species, comprising 12 genera and 8 families. Six species and one genus are newly described: Pyrgula sopianae sp. nov. (Hydrobiidae: Pyrgulinae), Asymmetrorbis pseudovitrina gen. et sp. nov., Gyraulus ianus sp. nov., Gyraulus magyari sp. nov., Gyraulus pseudodalmaticus sp. nov. (Planorbidae), and Potomida schneideri sp. nov. (Unionidae), all of which are endemic to Lake Mecsek. Based on a biogeographical analysis of selected Central to Southeastern European Early–Middle Miocene freshwater mollusk faunas, we find strong affinities between the Mecsek fauna and coeval assemblages of the Southern Pannonian Basin. These faunas show about equal similarity to those of the Dinaride Lake System in the south as well as to Central European ones in the north, rendering the Southern Pannonian Basin and Lake Mecsek in particular as an important stepping stone c