Fossil Facts > Ammonite

Ammonites are one of the most iconic fossils that often come to peoples’ minds when they think of a fossil. An ammonite was a squid-like creature that lived inside a coiled shell. This shell was divided into chambers. The animal itself only occupied the first chamber (the body chamber) whilst the rest played a part in buoyancy control.

Ammonites were prehistoric members of a class of animals called cephalopods, which are represented today by the squid and octopus. Ammonites appeared in our oceans in the Early Devonian period (approximately 415 million years ago) and lived until the end of the Cretaceous period (66 mya) disappearing in the mass extinction event that killed the dinosaurs (and many other groups of animals).

Ammonites were once called ‘snake stones’, as they were once believed to be coiled up snakes turned into stone, long before scientists came to realise what they really were.

Here at Lyme Regis, a large variety of different ammonites can be found, which can also be preserved in several different types of minerals. The most popular (and often the easiest to find) are ammonites preserved in the mineral pyrite.  Pyrite is a shiny brassy yellow mineral and its common name is ‘fool’s gold’ because it resembles gold. There are also ammonites preserved by the mineral calcite.  These are usually found inside the hard limestone rocks and particularly within a ball of limestone that form naturally within the muds and clays.  These round (and sometimes flying saucer shaped) limestone balls are called nodules. Identifying a nodule often requires practise and experience in recognising them and it is not easy to find the right type of rock which may house a calcite crystal ammonite inside.