Gryphaea dilatata

Jurassic

Phylum: Mollusca
Class: Bivalvia
Order: Ostreoida
Family: Gryphaeidae

Umbo
Growth lines
Two articulated valves

Mineral replacement of shell

Asymmetric valves distinctive for Gryphaeidae - flat upper (right) valve and curved lower (left) valve. With this shape Gryphaea reclined in the sediment, filter feeding.

Repair scars are visible on most Gryphaea specimens. When the animal was attacked unsuccessfully by a predator, a small amount of a growth line at the edge of the shell would have been chipped away. The next growth line would have filled in the missing part of the shell, leaving an uneven growth line pattern, with a 'v' or 'u' shape visible.