The seashells on this gallery might look like a collection found on a beach, but these are all fossil shells and are millions of years old, some dating back to before the dinosaurs. Seashells fossilize well because they are so hard. They are among the easiest fossils to find. Most are shells of mollusks—soft-bodied invertebrates such as snails and clams.
FAMILY FACT FILE
All the spiral shells on these pages were made by sea-dwelling gastropods (the class of mollusks that includes snails, slugs, and limpets). Just like garden snails, shelled gastropods can hide inside or under their shells for protection. The soft body within consists mainly of a single large muscular foot.
These mollusks have two shells joined by a hinge so they can snap shut. Cockles, clams, scallops, mussels, and oysters are all bivalves.
Mollusks date back some 500 million years to the Cambrian Period.