4.9" Fossil Fish (Cockerellites) - Wyoming

Cockerellites liops is a species of extinct temperate bass found in the Eocene aged Green River Formation of Wyoming. It is characterized by a sunfish-like body and its stout dorsal and anal spines. It was originally placed in the Priscacara genus but was moved to the newly created genus Cockerellites by D. Jordan and H. Hanibal in 1923. There is still some debate among researchers about whether this new genus is valid.

Cockerellites is found in large numbers in mid-lake deposits, representing 5 to 20 percent of the fish unearthed, depending on the layer. It is considerably rarer in shoreline deposits, representing only 1 to 2 percent of the fish found. Because of this, Cockerellites is thought to have been a schooling fish. Fossils have been found at a maximum size of about six inches, but they rarely exceed five inches in length.

At first glance, Cockerellites liops has a very similar appearance to the rarer species Priscacara. Size can often be used as a differentiator, since Cockerellites did not exceed 6 inches while Priscacara serrata is typically found in excess of 6 inches. Cockerellites also has more dorsal and anal fin rays than Priscacara and a much smaller mouth.

About Fossil Lake

50 million years ago, in the Eocene epoch, these fish thrived in Fossil Lake, which was fed by the 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: 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.