Who: Heliobatis radians
Lagerstätte: Green River Formation
What: Heliobatis is a freshwater stingray that lived in Wyoming during the Eocene period. At the time, Wyoming used to be much warmer and wetter than it is today (think Louisiana) and was filled with freshwater lakes. Stingrays are cartilaginous fishes related to sharks. As such, its rare to have complete stingrays in the fossil record as they mostly lack hard parts; usually you would fine their teeth, scales or stings if you’re lucky. However, the Green River Formation, where Heliobatis is found, is one of two places in the entire world with complete stingray fossils (and the only site with freshwater ones). This is because the stingray’s lakes had a salty and anoxic bottom so when they died they fell to the bottom of the lake where they’re eventually burried and preserved almost to perfection.
“Freshwater stingrays of the Green River Formation of Wyoming (early Eocene), with the description of a new genus and species and an analysis of its phylogenetic relationships (Chondrichthyes, Myliobatiformes),” Carvalho et al. 2004
(Link is a download pdf provided by AMNH)