Ammonites were a group of mollusks living in the sea, which includes the current squid. Today these animals have their shell inside, but the Ammonites still had their shell outside the body, just like snails.
The ammonite is about 112 million years old and completely fossilized. This specimen has been sawn through and polished. This makes the different rooms nicely visible. The two halves together form a pair and give a nice picture of how the ammonite grew slowly by expanding its shell with a small chamber.
Fossil ammonite from Madagascar
The most beautiful ammonites are found in Madagascar and can measure up to 25 centimeters in diameter. This ammonite belongs to the Cleoniceras family. Calcite crystals are found in some hollow chambers. These are actually crystal geodes within the fossil. Ammonites became extinct about 65 million years ago, just like the dinosaurs.