GeoPicture of the Week: Crinoid Fossils

Crinoids are marine animal (not plants) that have been around since the late Cambrian, some 500 million years ago. Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults. They are very fragile and require specific conditions to be preserved, so fossils like this one are very rare indeed.