Hypowaagenia nov. gen., a rare genus of giant aspidoceratid ammonite from the Upper Jurassic of Southern Germany

Abstract

A new genus, Hypowaagenia (type species: H. endressi nov. sp.), is introduced for previously unknown large-sized macroconchiate aspidoceratid ammonites with an umbilical and a ventrolateral row of spines. In the medium and adult stages irregular ribs interconnect these spines. The oldest unequivocal record of this genus comes from the Early Kimmeridgian Planula Zone, whereas the type material of H. endressi nov. sp. comes from the upper Platynota Zone/? lowermost Hypselocyclum Zone. Corresponding microconchs have not yet been identified. Although all unequivocal records come from Southern Germany, a Tethyan origin is most likely for these aspidoceratids. Another, stratigraphically younger species tentatively included in Hypowaagenia is Aspidoceras acanthomphalum (Zittel, 1870), which is, however, only recorded yet by mesoconchiate specimens. The ammonite fauna of the type horizon of H. endressi nov. sp. is briefly characterized and termed as the geniculatum Biohorizon of the late Platynota Zone.