Ammonites are extinct animals. They lived between 400 and 65 million
years ago. They lived in the Paleozoic and Mesozoic oceans.
Paleontologists classify ammonites as relatives of modern animals such
as the squid, the octopus, and the nautilus. This group of organisms is
called the Cephalopods, belonging to the Phylum Mollusca.
All cephalopods are invertebrate animals, or animals without
backbones. In addition, the cephalopods all have chambered shells.
Ammonite and nautilus shells have a whorl or plano-coiled shape.
The shell of the ammonite is usually what is preserved as a fossil.