Taxonomy and Palaeobiogeography of the landgastropods of the Miocene silvana- and sylvestrina-beds in SW Germany

Abstract

The most common continental stratigraphic units in the SW-German Miocene are the the silvana-beds deposited prior to the Ries meteorite impact, as well as the post- Ries deposited sylvestrina-beds (MN6-MN9). They contain a lot of different landgastropods, which were studied with respect to taxonomy (including morphometrics), palaeogeography and palaeoecology. The index fossils Palaeotachea silvana and P. sylvestrina could be clearly separated with morphometrical and statistical methods (Cluster analyses, PCA). Additionally, four other Palaeotachea species could be identified in the studied SW German Miocene deposits. At least 35 different species of landgastropods could be identified and illustrated from the silvana-beds based on the deposits of Dischingen, Hohenmemmingen and Mörsingen. The contemporaneous sediments of Randeck Maar (MN5) provide insights into the gastropod diversity of an ancient Maar lake. All in all 32 different continental gastropod taxa were identified from this locality. In the younger sylvestrina-beds of the Steinheim Basin (MN7), 48 different landsnail species could be described and illustrated. Taxonomic problems concerning the Chondrinidae from the sylvestrina-beds were solved as well as the genus membership of Pseudochlorits insignis. The majority of the landgastropods were hydrophilic species and a lot of them have Recent relatives. However, the sylvestrina-beds contain a higher proportion of xerophilic taxa. According to the ecological preferences of the single taxa, different micro-habitats could be reconstructed. During the research approximately 180 type specimens of continental gastropods could be identified in the collection of the SMNS which were illustrated in a type catalogue. Additional to the taxonomic work, statistical methods (Cluster and NMDS analyses) were used to compare all published Middle Miocene continental deposits in Middle Europe. The resulting clusters reflect the palaeogeographic situation of that time interval. Finally, the taxonomic results were also used for a species catalogue for the silvana-beds at the southern margin of the Swabian Alb.