Bivalves
Bivalves are another group of mollusc that you can recognise today. Cockles, mussels, and oysters are all bivalves.
They live inside shells with two parts, known as valves, that are usually mirror images of each other. These valves open so the animal can feed, and close to give the animal protection.
All bivalves live in water, and most of them are found in the sea. They feed by filtering out small food particles from the water around them. Most live buried in sand or sediment. Some can attach themselves to hard surfaces or bore into rock. A few can even swim.
The oldest bivalve fossils are over 500 million years old.
Because bivalves are still common today we know a lot about how they used to live. You can find fossil bivalves that look very like modern bivalves.
Fossil scallop shells
Gryphea, sometimes called the devil's toenails
The shape of their shells can tell palaeontologists if they swam or if they burrowed, and the type of environment they lived in.
Huge numbers of fossil bivalve shells can form limestones.
