Stingray Heliobatis sp.

The Heliobatis stingray, a member of the whiptail ray family, are among the most striking species in the Green River fauna. The stingrays reached a meter in length and fed on fish, mollusks, and crustaceans. Stingrays are often found in areas where the remains of river crayfish and shrimp are abundant.

Most stingrays live in the seas, but some have adapted to freshwater reservoirs. Modern freshwater stingrays can be found in the Amazon basin. In the Eocene, about 50 million years ago, stingrays were widespread in Wyoming, home to a system of large lakes, rivers and swamps. Their sediments formed the Green River Formation, rich in fossilized fish.

The fossils of stingrays from Green River are a perfect example of how fine tissue structures of a living organism can be preserved in rocks. Stingrays are cartilaginous fish, meaning that they lack a bony skeleton. Their cartilage and soft tissue imprints are preserved thanks to calcium carbonate-rich silt and the increased salt concentration in the water. Such conditions were created during the arid seasons, when drying ponds became traps for fish and other animals.