Land snails from the Miocene Steinheim impact crater lake sediments (Baden-Württemberg, South Germany)

Although the Middle Miocene (Mammal zone MN7) freshwater deposits of the impact crater of Steinheim am Albuch (Steinheim Basin, SW Germany) are famous for their fossil mammal and freshwater gastropod fauna, the rich land snail fauna has not been studied for almost 100 years. A re-study of the available material resulted in the identification of 48 species belonging to the following genera (number of species in brackets): Cochlostoma (2); Carychium (1); Oxyloma (1); Pseudoleacina (1); Palaeoglandina (1); Azeca (1); Cochlicopa (1); Strobilops (1); Truncatellina (1); Vertigo (4); Gastrocopta (3); Negulopsis (1); Granaria (3); Vallonia (3); Gibbulinopsis (1); Pupilla (2); Triptychia (1); Pseudidyla (1); Opeas (1); Cecilioides (1); Punctum (1); Discus (1); Janulus (1); Aegopinella (2); Oxychilus (1); Vitrea (1); Archaeozonites (2); Vitrina (1); Helicodonta (1); Leucochroopsis (1); Apula (1); Pseudochloritis (1); Megalotachea (1); Arion (1); Milax (1). Steinheim am Albuch is also the type locality of 26 Miocene land snail taxa. The fauna covers a whole range of different terrestrial ecological niches from very wet habitats (Oxyloma) to very dry ones (Granaria). In contrast to the older silvana-beds (MN5), the Steinheim deposits contain three clearly distinguishable species of Granaria. This genus is the most abundant land snail in the Steinheim deposits, implying a dryer and warmer climate than during the deposition of the silvana-beds. The genus Klikia, which is common in the silvana-beds, is absent. Among the 34 genera, 24 are extant and most of them (21) are also part of the Recent land snail fauna of Europe. The remaining three genera occur today in North, South and Central America (Strobilops); North and South America, Cap Verde Islands, North Africa, Siberia, Central and East Asia, Australia, Pacific Ocean islands (Gastrocopta); Canary Islands and Madeira (Janulus). The slugs could only be roughly determined by their vestigial shells.