5.05" 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.

Specimens like this come from the coveted 18 inch layer of the Green River Formation, which produces darker and more detailed fish than the majority on the market. The rock from this layer is much harder and more durable than other layers in the formation, likely due to its initial deposition conditions in deep water. Because of these conditions, fish found in the 18-inch layer can be extracted whole and in excellent condition. This layer is typically collected at night using low-angle light to see the bump in the rock that the fish's backbone creates. They then cut these fish out and take them to a lab where the fish, which may be up to an inch under the surface of the rock, are meticulously extracted under microscope with hand tools.

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.