Swimming abilities of ammonites and limitations

Using some typial ammonites from the Posidonia shales, the aperture orientation, the ideal direction of propulsive thrust, the stability and the buoyancy of the living animals and of the empty shells were investigated as a function of the body chamber length. The emerging limitations indicate that ammonites were hardly suited for a nectonic mode of life. Only in case of favourable conditions empty shells could ascend to the surface and drift.