Early Jurassic (Pliensbachian)gastropods from Franconia, Southern Germany

Abstract

40 nominate gastropod species are described from the Early Jurassic (Late Pliensbachian) Amaltheenton Formation of Franconia (Northern Bavaria, SouthernGermany). In addition 11 species are treated in open nomenclature.Most of thematerial comes from the clay pits at Buttenheim and Kalchreuth. The gastropods occur in grey shales representing former marine soft bottom environments. Gastropods are the most diverse and locally even the most abundant taxonomic group comprising the benthic communities of the Amaltheenton Formation in Franconia. Bivalves, scaphopods, ophiuroids, crinoids and brachiopods are also abundant. Among bivalves, the oyster-likePlicatula spinosa andNuculoidea are especially abundant.The gastropods andmost of the other benthic species are small (< 15 mm) or even minute. Only three gastropod species attain a size >50 mm: Pleurotomaria amalthei, Pseudokatosira undulata and Buttenheimia dietzi. However, these large species are rare. The most abundant gastropods are the caenogastropods Levipleura blainvillei, Kalchreuthia frankei and Francocerithium kochi and the heterobranch Domerionina domeria.Heterobranchia, especially architectibranchs (formerly Opisthobranchia) have the highest species diversity among gastropod subclasses or orders. Eleven species are described as new: Striatoconulus? trimeuselensis, Costasphaera franconica, Cryptaulax johanni, Purpurina liassica, Tripartella neubaueri, Buttenheimia dietzi, Tricarilda schoberti, Tricarilda recta, Camponaxis jurassica, Schobertinella heterogyrata and Sulcoactaeon sendelbachensis. Three genera are described as new: Costasphaera, Buttenheimia and Schobertinella. The validity and identity of the genera Pseudokatosira andKatosira is discussed based on the study of the holotypes of both of the disputed type species ofKatosira:Katosira periniana (Early Jurassic, France) orKatosira fragilis (Late Triassic, SouthernAlps).We conclude that K. periniana is correctly considered to be the type species. Both holotypes are illustrated and re-described here.