Fossil Information: Oyster Gryphaea, also known as the "devil's toenail," is an extinct genus of mollusks belonging to the family Gryphaeidae. These bivalve organisms are particularly distinctive for their unique shell shape, resembling a curved, elongated toenail, hence the colloquial name.

Description: The shell of Gryphaea is generally thick and irregularly shaped, with one valve being more convex and the other more concave, giving it a distinct appearance. Its size could vary greatly, from just a few centimeters to over 30 centimeters in length. The exterior of the shell typically exhibits fine concentric ridges and often has a rough texture due to its mode of attachment to the substrate.

History: Gryphaea first appeared during the Jurassic period, around 200 million years ago, and persisted until the end of the Cretaceous period, about 65 million years ago. They were widespread throughout the world's oceans during their existence, inhabiting shallow marine environments such as coastal regions and continental shelves.

These organisms were filter feeders, meaning they obtained their food by filtering small particles from the water column using their gills. They likely lived in colonies attached to hard substrates such as rocks, shells, or even the remains of other organisms.

Gryphaea fossils are relatively common and have been discovered on every continent. They are particularly abundant in certain geological formations, such as the Jurassic Coast in England, where they are found in large numbers embedded in limestone and shale deposits.