Ammonite fossils are the remains of prehistoric sea creatures that are spiralled in shape and resemble a ram's horn. According to Cochise College, ammonites first appeared approximately 450 million years ago and became extinct at the end of the Cretaceous period about 65 million years ago.
Ammonites were cephalopods whose modern-day relatives include octopuses, cuttlefish, squid and the nautilus. The nautilus also possesses a spiral-shaped shell and is one of only two types of extant cephalopods that has an external shell. According to the Smithsonian National Zoological Park, the chambered nautilus may live 15 years or more, an unusually long lifespan for a cephalopod.