How to recognise them

Curved ridged shell.

Fossil Info

Gryphaea is an extinct marine oyster. It is a type of shellfish called a bivalve, which had two shells or valves that were joined or hinged at one end allowing them to open their two shells. Modern bivalves include clams, cockles, mussels and scallops. Gryphaea evolved around 200 million years ago and went extinct about 34 million years ago. They are distinctive due to the large curved shape of one of their shells. This large shell often has ridges preserved - these are growth lines. The second shell is much smaller, flat, and flips open like the lid on a toilet seat. 

Fun Fact

The common name for Gryphaea is  'the Devil's toenail' due to the curved and ridged shape of its larger shell.