One of the most interesting aspects of fossil collecting is learning about the folklore attached to them, and few fossils rival Gryphaea when it comes to this sort of thing! Known as ‘devil’s toenails’ because of their curves and gnarly shape, during medieval times they were used in magical treatments for arthritis and other types of painful joints.
This is a classic example of what folklorists call sympathetic magic, where something that looks like another thing is used to influence or banish that thing. Other examples included the use of ammonites (as ‘snake stones’) to combat snakebites, and loaf-shaped Cretaceous-era sea urchins (as ‘fairy loaves’) as charms in bakeries to ensure the quality of the bread produced there.
Whatever their magical value, Gryphaea are in fact a genus of oyster that were inhabitants of warm, shallow seas for an unusually long period of time. First appearing in the late Triassic about 230 millions years ago, Gryphaea-type oysters were hugely diverse during the Jurassic and Cretaceous, but unlike a lot of the organisms we associate with Mesozoic faunas they persisted into the Tertiary, the last ones into dying out in the Eocene. Actually, it’s a bit more complicated than a single lineage of oysters persisting for hundreds of millions of years, and some geologists prefer to limit the use of Gryphaea to only one particular, strictly Jurassic branch of the oyster family Gryphaeidae. Later species belong to allied, but distinct, genera such as Exogyra and Pycnodonte.