What did fossil cephalopods eat, and what ate them?
All living cephalopods are predators, and fossil belemnites appear to have been predatory as well. Fossilized gut contents of ammonites are quite well known, and are good evidence for this, and include mostly small invertebrate fragments. Crustaceans such as shrimps and ostracods, pieces of echinoderms, and foramaniferans suggest that ammonites tended to eat small or inactive animals, perhaps scooping in mouthfuls of sediment and sorting the food from the sand in the buccal cavity. Open water, pelagic ammonites may have eaten small zooplankton. The hooks on the arms of belemnites and the various fossil squids indicate a more active predatory lifestyle, probably based on catching smaller fish and other cephalopods. As in modern seas, fossil cephalopods were important parts of the marine food web. Ammonites in particular are frequently found with damaged shells, showing that they were frequently attacked. Marine reptiles, large fishes and other cephalopods were probably the main predator
