Regurgitalites – a window into the trophic ecology of fossil cephalopods

Fossil oral ejecta that exclusively contain bivalved calcitic lower jaws of ammonites (= aptychi) from Late Jurassic Solnhofen-type deposits of southern Germany are described. Based on the symphysis length of aptychi the ammonite shell diameters were reconstructed, ranging from 5 to 170 mm. To identify the potential ammonite predator published reports on stomach contents, coprolites, and ammonite-palaeopathology were critically assessed. Implementation of the actualistic approach, together with some functional considerations, includes the identification of modern cephalopod predators with focus on the modern Nautilus, and the distribution of vomiting behaviour among them. Stomach fluid pH is also important because species with an alkaline stomach pH are unable to dissolve calcareous hardparts and require to orally eject such material. Herein, we regard coleoids with an opportunistic diet as the most likely producers of the aptychi-bearing regurgitalites. This is based on finds of aptychi in the stomachs of the two coleoids Plesioteuthis and Trachyteuthis. They were likely fast, highly manoeuvrable swimmers. Both share a strong, triangular-shaped jaw apparatus that could possibly crush ammonite shells as well as arms equipped with suckers to hold their prey. Circumstantial evidence for coleoids as the producers comes from the alkaline pH of the stomach fluids of modern coleoids.