ammonite

1. (paleontology) Any of an extinct group of cephalopods of the subclass Ammonoidea; a fossil shell of such an animal.Examples: "Ammonites floated through the world's shallow oceans for more than three hundred million years, and their fossilized shells turn up all around the world."; "Visit the Jurassic Coast World Heritage Site in the UK, and ammonite road signs greet you at every town and city and even the lampposts on the seafront feature a familiar coiled shell."; "There are a few well known shelled giant cephalopods from the fossil record. Some of the largest recorded ammonites are in the genus Parapuzosia, fossils of which reach up to 2m in diameter."Synonyms: ammonid, ammonoid