Ammonites / Ammonoids — Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids — octopus, squid, and cuttlefish — than they are to shelled nautiloids such as the living Nautilus species. The earliest ammonites appear during the Devonian, and the last species vanished in the Cretaceous–Paleogene extinction event. 
If you fancy a read or would like to see some photos of ammonites, check out the Fossil Huntress Blog ARCHEA at https://fossilhuntress.blogspot.com/ or visit the Fossil Huntress page on Facebook.