This is a nicely preserved, 5.1" long Cockerellites (Priscacara) liops fish from the famous 18 inch layer of the Green River Formation. It was collected from Lindgren Quarry near Kemmerer, Wyoming.
50 million years ago, in the Eocene, these fish thrived in Fossil Lake, which was fed by Uinta and Rocky Mountain highlands. The anoxic conditions at the bottom of Fossil Lake slowed bacterial decomposition, prevented scavengers from disturbing corpses, and most interestingly, suffocated creatures that ventured into the oxygen-starved aquatic layer. The result is a miraculous exhibition of Eocene biota in a subtropical aquatic community within sycamore forests teeming with creatures such as freshwater stingrays, dog-sized horses, menacing alligators, early flying bats, and one of the first primates.