Block of Ammonites, Nautiloids and Fossilised Shells

Ammonites are an extinct group of marine mollusk, their name given by Pliny the Elder because of the resemblance to the ram’s horns of Ammon, the Egyptian god of life and procreation. Widespread and diverse in Jurassic and Cretaceous periods, ammonites soon died out, but have been found world wide. Ammonites are part of the cephalopod family, along with Nautiloids (shell dwelling creatures) and Coleoids (shell-less mollusks, like squid and octopuses). Ammonites were born with one tiny shell and built new chambers as they grew – thereby creating the segmented shell that can be seen here in this fine example. They would have moved into the new chamber, sealing off the older, smaller chambers – these older chambers were also filled with gas, allowing the ammonite to control its buoyancy. Ammonites first appeared around 450 million years ago, during the Paleozoic Era, and became extinct around 66 million years ago, at the end of the Cretaceous period. The last ammonites became extinct at the same time as the dinosaurs, in a mass extinction called the Cretaceous-Paleogene extinction, which is believed to have been caused by an asteroid colliding into Earth.