Bivalve oyster shell
Oysters encrusted with tubeworms
These two fossils are an extinct kind of oyster called Gryphaea. They have two shells, and as you can see on the top specimen, one shell is much larger than the other. The shell opened to allow water to be drawn inside and filtered for food. If you look closely, you’ll see that the top specimen is encrusted with tubeworms which bored into the shells – they also filter the water for food.
These specimens are from the Upper Jurassic period, when the Gryphaea became much larger than its ancestors in the Lower Jurassic. The smaller fossils were commonly known as ‘Devil’s Toe Nails’.
Find out more about bivalves on the molluscs pages.