Ammonites are a type of cephalopod, distantly related to the modern day octopus, cuttlefish and nautilus. They had coiled shells which contained gas chambers - a feature of many cephalopods.
Only the final chamber next to the opening was occupied by the animal. As it grew, the animal periodically moved forwards and formed a new septum (division) at the rear of the body chamber. Older chambers were filled with liquid and gas, the proportions of which could be changed to allow the animal to move up and down in the water column.
Ammonites were named after the ancient Egyptian god "Ammon" who was depicted as having ram's horn on his head.
Ammonites had well developed eyes, jaws and tentacles and swam using a type of jet propulsion. It would ingest water through its mouth and any excess was shot out through a hose like structure under the body propelling the animal backwards through the water. The largest ammonite ever discovered was the size of a tractor tyre.
