After a regression phase of the Paratethys Sea at the Serravallian/Tortonian boundary, a brackish lake – Lake Pannon - formed within the Pannonian Basin. Based on this change of physiochemical conditions a remarkable adaptation of dinoflagellates occurred. In an ongoing study we illustrate how a well established and moderately diverse marine community almost disappeared, leaving only a few numbers of well-adapted dinoflagellate species. For this study, species composition and dynamics of dinoflagellate communities in the western part of Lake Pannon were considered at two locations (Mataschen, Styrian Basin; Hennersdorf, Vienna Basin). All the studied samples are rich in dinoflagellates, however, a low number of species was encountered. In contrast, to the high diversity of the Early and Middle Miocene of the Central Paratethys, the main representatives of the lake ecosystem are few gonyaulacoid and peridinioid taxa.

In this study, several species of Spiniferites and Selenopemphix were selected to trace their morphological variations in response to changes of the lake’s physicochemical conditions (e.g. salinity, nutrients). In Spiniferites bentorii especially cyst ambitus, size, processes’ morphology and the development of the apical boss are changing in reaction to environmental changes, while in Selenopemphix sp. cyst size and the density and type of surface ornamentation show distinct variations. Altogether a correlation of morphological characters and ecological parameters of highly abundant gonyaulacoid and peridinioid taxa of the Pannonian Basin System can be demonstrated.