A mixed marine/non-marine mollusk assemblage from the Middle Miocene of Hidas (Hungary)

We describe a mixed assemblage of polyhaline, freshwater, and terrestrial mollusks from late Middle Miocene (early Serravallian, late Badenian) strata near the town of Hidas, southern Hungary. It comprises 19 species in 16 families - seven polyhaline to normal-marine gastropod species (Neritidae, Hydrobiidae, Nassariidae, Potamididae, Batillariidae, Litiopidae), four gastropod and one bivalve species from freshwater settings (Lymnaeidae, Planorbidae, Sphaeriidae), and seven species of terrestrial gastropods (Ellobiidae, Strobilopsidae, Vertiginidae, Gastrocoptidae, Discidae, Gastrodontidae, Elonidae). The polyhaline/marine taxa identified to the species level are widely distributed species, all of which have been previously reported from Hidas. The freshwater and terrestrial species, in turn, all represent new occurrences. Most of them are common components of Middle Miocene peri-Paratethyan non-marine faunas. Biostratigraphically, the fauna agrees with the early Serravallian (late Badenian) age suggested by a previous study on microvertebrates. We provide a systematic account of all species, along with a critical discussion of the non-marine species previously recorded from Hidas. The assemblage was likely deposited in a low-energy freshwater setting, perhaps a pond, oxbow lake or backwater swamp. We assume that the brackish elements were transported from a nearby mudflat or mangrove environment, perhaps during an overspill or flooding event.