Ammonites are extinct squid. They lived from about 400 to 65 million years ago. Their wounded house was divided into rooms by partitions: as they grew, a room was added. Only the last room was inhabited. By means of gas and water in the old rooms, the animal could move up and down in the water. They caught crabs and shrimps with their trapping arms. As a fossil, it is usually not the shell that is found, but its petrified core.