Environmental changes and diversification ofCyprideis in the Late Miocene of the Styrian Basin (Lake Pannon, Austria)

Abstract

The turnover from the Sarmatian Paratethys Sea into Lake Pannon around 11.6 Ma seriously impacted aquatic biota like ostracods and triggered their adaptation to the changed environments. One survivor of this ecological switch is certainly the genusCyprideis, which is well known for its radiation in Lake Pannon. A high-resolution micropalaeontological investigation of a transgressive-regressive sedimentary cycle just above the Middle/Late Miocene boundary focused on the taxonomy of the foundCyprideis species. Species-diagnostic characters were evaluated applying qualitative as well as lineal and geometric morphometric analyses. These examinations led to the introduction of two new ostracod species (Cyprideis kapfensteinensisGross n. sp. andCyprideis mataschensisGross n. sp.), which diverge only indistinctly in outline, but are undoubtedly separated by their size and hinge structure along with considerable differences in number of posteroventral spines. We conclude that these co-occurring species were two sympatric species, which were probably adapted to different microhabitats.C. kapfensteinensis is only recognised in the interval at the peak of the transgression, which corresponds to the maximum deepening of the lake in this area and with meso-/polyhaline conditions. In contrast,C. mataschensis seems to be a more euryplastic species because it appears well before this event and is also recorded in the regressive prodelta sediments up section.