Green River Formation is a group of ancient lake beds deposired around 48 million years ago in what is now SW Wyoming, The calcium carbonate saturaed waters and the low energy environment of the lakes provided an excellent chemical and physical mode of preservation. Bpnes do not dissolve as readily as the dead animal lays on the lake bed, it gets covered with a very fine layer of carbonate mud repeatedly. GRD is considered a lagerstätte, which is a term used to describe an area with exceptional biodiversity and fossil preservation. There is a wide range of species preserved throughout the lake bed environments. Birds, bats, horses, snakes, stingrays, insects, leaves, snails, turtles, crocodiles, and many more animals can be found within the carbonate shales.