Hydrostatics of fossil ectocochleate cephalopods and its significance for the reconstruction of their lifestyle

The importance of hydrostatics for ectocochleate cephalopods and for the reconstruction of their lifestyle as well as the implications of hydrostatics and further physical conditions for the ontogenetic shell formation process are discussed. The method used by some authors of merely assuming neutral buoyancy is criticized as not allowable, since even in case of the theoretically possible condition of neutral buoyancy the obligatory vertical shell orientation in orthoconic forms would definitely preclude a horizontal swimming capability. The often presumed neutral buoyancy follows from an old misunderstanding with regard to the original function of the phragmocone, which was modified and amplified only in the course of evolution. The idea of a benthic lifestyle of fossil ectocochleate cephalopods in a gastropod-like fashion is maintained and extended to further palaeozoic forms.