Middle Ottnangian (Late Burdigalian) mollusks from the Rott Valley (SE Germany): the ultimate marine fauna of the Western Paratethys

The Bivalvia and Gastropoda from the Upper Marine Molasse deposits of the lower Rott Valley (North Alpine Foreland Basin, Lower Bavaria, SE Germany) comprise the first mollusk fauna of middle Ottnangian age (ca 17.5 Ma) to be documented in detail. Altogether, the assemblages from Brombach, Kainerding and Anzenkirchen yielded 27 species of Bivalvia and 9 species of Gastropoda. The bivalve species Spisula brombachensis n. sp. is described as new to science, and Aequipecten camaretensis is first reported from the Ottnangian of the North Alpine Foreland Basin. Furthermore, the well-preserved material allowed for the taxonomic revision of the Ottnangian index fossil Pecten herrmannseni. The bivalve community is dominated by suspension feeders, mostly shallow, soft bottom dwellers (Glycymeris, Anadara) and cementing epifauna (Ostrea). Gastropods almost exclusively comprise carnivorous browsers and predators. The parautochthonous assemblages are indicative of normal marine, well-oxygenized sandy-silty shoals at a water depth of presumably less than 20 m. Except for the presence of a single estuarine Crassostrea, the middle Ottnangian fauna is not indicative of reduced salinities. Consequently, the paleoenvironmental turnover to the brackish-water fauna of the directly overlying upper Ottnangian deposits of the Rzehakia Lake was abrupt. Glycymeris–Anadara–Ostrea communities similar to the one recorded from the Rott Valley are widespread in European seas and beyond during the Neogene and Quaternary.