Eocene
Class Chondrichthyes, Subclass Elasmobranchii, Superorder Batoidea, Order Rajiformes, Family Dasayatidae
Green River Formation, Fossil Lake, Kemmerer, Wyoming

Rays belong to the Class Chondrichtyes along with sharks. Their inner skeletons are cartilage, not bone, and thus have more organic material that decays more readily. Fossils of cartilaginous fishes relatively rare. The Green River Formation is a famous American Lagerstätte fossil site.