Hildoceras ammonite from Somerset England
These English ammonites belong to the genus Hildoceras and lived about 180 million years ago in the lower Jurassic. They are found in Somerset in the Junction Bed, Falciferum zone. The front of the ammonite is polished to make the different chambers visible. The other side is left natural to see what the shells looks like.
What were ammonites?
Ammonites were a group of molluscs living in the sea to which the present squid also belongs. Nowadays these animals have their shell inside but the Ammonites still had their shell outside the body, just like snails. Ammonites, like dinosaurs, died out about 65 million years ago.
Small geodes in the rooms
Every time the room in which the ammonite lived became too small, they built a larger one on top of it. In some ammonites the hollow chambers are filled with crystals, these are calcite crystals that form a geode within the fossil.