7.8" Diplomystus Fossil Fish With Knightia - Wyoming

Diplomystus is an extinct genus of freshwater, ray-finned predators that are distantly related to modern herrings and sardines. Diplomystus has a distinctive jaw that protrudes aggressively outward from the mouth at an angle that allowed it to feed in surface waters and devour such prey as the smaller, schooling, Knightia.

50 million years ago, in the Eocene (55.8 mya to 33.8 mya), D. dentatus thrived in lakes fed by Uinta and Rocky Mtn. highlands. A voracious predator and delicious prey, D. dentatus is uniquely entombed in the fine-grained, lime mud of Fossil Lake.

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.

By the end of the Eocene, Earth developed icehouse climate characteristics and had a change in atmospheric chemistry. The effects of bolide impacts may also have contributed to the eventual loss of flora and fauna at once verdant latitudes.

Today the wonderfully preserved fossils of Diplomystus and other Fossil Lake fauna are collected in several private quarries around Kemmerer, Wyoming. The best preserved fish fossils come from the coveted 18 inch layer. This layer is collected at night under high-powered lights allowing the faint signs of fish under the surface to be more easily observed. These “ghosted” fish then must go through many hours of manual preparation to remove the overlying rock and reveal the Green River fauna in all of it’s glory.

Knightia is an extinct genus of schooling, ray-finned, spindle-shaped, bony fish that shares a family with herrings and sardines. They lived in the freshwater (lacustrine) environments of North America and were eaten by just about everything that was bigger. They ate insects and smaller fish, and used gill rakers to feast on plankton. Knightia eocena is the largest of three species of Knightia, with a typical length of about 15 centimeters. It is the state fossil of Wyoming.

They have rows of dorsal and ventral scutes which ran from the back of the head to the medial fins. They had heavy scales, and small conical teeth. They are popular finds in the Wyoming lagerstätte, and were a primary food source to the large and hungry vertebrates of that once hunted the Green River Formation.

The Green River Formation is an Eocene, geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The Eocene spanned approximately 55.8 mya to 33.8 mya. This formation has distinct stratigraphy which displays alternating light and dark layers that represent seasonal erosion and deposition.

Fresh water basins, charged by Uinta Mtns. on the Wyoming-Utah border, contained an enormous representation of taxa. The beginning of the Eocene was marked by warm upper latitudes, a greenhouse atmosphere rich in methane and carbon dioxide, and local climates stabilized by large lakes populated by such creatures as crocodiles. Fossil Lake in Wyoming is known for its well-preserved warm, lacustrine ecology.

The end of the Eocene was dramatically different with the onset of icehouse climate characteristics, a change in atmospheric chemistry, and possible bolide impacts. The Green River fossils date about 48 mya, but cover several million years, including the transition between the moist early Eocene climate and the slightly drier mid-Eocene.