These are images of the shell of a modern animal, called Nautilus . The first, is an image of the outside of a Nautilus shell. The second, is an image of the inside of the shell after it has been sliced in half. There are many modern organisms with spiral shells. Snails have spiral shells. Some sea shells (clams, etc.) are spiral shaped. Some crabs use empty shells of snails and clams as their homes. If we cut any of these shells in half, they would have a different pattern than the fossils at the library. The modern animal with a shell most similar to the spiral fossils at the library is the shell of a modern Nautilus . The Nautilus is a squid that lives in a coiled shell. Nautilus is a member of the nautiloids, which are an order of cephalopods. Ancient orders of cephalopods included the coiled ammonites and straight-shelled belemnites . If Nautilus became a fossil, the squid (all soft parts) would not likely be fossilized. Only the shell (a hard part), as seen above, would remain. The chambers in the shell, and the way the chambers are organized in the shell are unique to cephalopods. When paleontologists (scientists who study fossils) find ancient shells with similar patterns they know they have found a cephalopod. Although the soft parts are not usually fossilized, paleontologists can use the modern Nautilus shell to suggest that the ancient cephalopods (ammonites, belemnites, etc.) had squid-like animals living inside of them.