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Gryphaea |
The shells of Gryphaea are common fossils in Jurassic rocks. They are better known by their folk name of Devil’s Toe-nails. This name refers to the curved shape of the shell. It was thought that carrying one could prevent rheumatism. Gryphaea are related to modern bivalves, such as oysters and cockles. They lived on the sea floor and filtered small particles of food from the water. If they were disturbed the flat top valve of the shell would be pulled tightly closed, protecting the animal from harm. The evolution of Gryphaea can be seen if you collect shells from different ages of the Jurassic.
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Gryphaea from the Middle Jurassic in life position. |
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Lower Jurassic Gryphaea |
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If a Gryphaea shell grows attached to an ammonite it gains the pattern of the ammonite shell on its own. |