Continental molluscs of the fossil site Sandelzhausen (Miocene; Upper Freshwater Molasse from Bavaria) and their value for palaeoecological assessment

The continental mollusc fauna of Sandelzhausen (Southern Germany, Early/Middle Miocene, MN5) is presented and shown to consist of 66 snail and 3 bivalve taxa. Previous ecological interpretations were partly based on poorly preserved material and are shown to be erroneous. Within a series of quantitative samples, ecologically four mollusc communities can be distinguished (two each for terrestrial and freshwater molluscs), highly indicative of ecological conditions and changes in the landscape surrounding the fossil site as well as the locality itself. Open scrub-lands with temporary waters, as indicated by forms such as Granaria and the dominance of lymnaeids, are steadily replaced with damp forests with abundant litter and rotting wood surrounding a perennial lake with small tributaries. These more favorable conditions are indicated by an overall increase of mollusc diversity, rising abundance of planorbids, and presence of restricted forms such as Drepanotrema (intolerant to droughts) as well as certain forest dwellers such as Gastrocopta and hygromiids. Molluscs are highly sensitive to environmental changes, which is reflected in the fossil record of Sandelzhausen.