Gastropods and scaphopods have aragonitic shells and are in the Muschelkalk generally preserved as internal moulds that do not show any shell ornamentations. However, if their instable nacreous conchs are replaced by more stable minerals, it becomes clear how diverse gastropod faunas can be. Such ‘Ersatzschalenfaunen‘, with the original aragonitic shells replaced by calcite, dolomite, or silica admit the best impression of the real Muschekalk faunal diversity.
Internal mould (‘Steinkern‘) of the big gastropod Chemnitzia hehli from the Upper Muschelkalk of Crailsheim
Wortheniella, a slit-bearing archaeogastropod from the Upper Muschelkalk of Wiesloch, with its original shell replaced by dolomite
Scaphopods are mollusks with a tube-shaped shell resembling an elephant’s tusk with an open tip. They are indicative of muddy sediment, from which they collect nutrients. The picture shows calcitic ‘Ersatzschalen‘ of Plagioglypta from the Lower Muschelkalk.
The gastropod beds, which are quite common in the Jena Formation, are dominated by Ophaloptycha gregaria preserved as internal moulds. The aragonitic shells of the figured specimens were replaced by calcite and naturally prepared by humic acids.
In the extremely diverse reef biota of the Late Triassic Cassian Formation of the Dolomites several hundreds of gastropod species lived among countless other invertebrates. The excellent preservation of their original aragonitic shells may also give an idea of the diversity of the Muschelkalk gastropods, which are normally preserved as steinkerns.
Neritaria interscripta and N. matercula from the Lower Grey Marl Horizon of the Hohenlohe Lower Keuper may even have preserved spiral colour bands of their shells.