6.25" Prehistoric Diplomystus Fossil Fish

Here is a very detailed, 6.25" long prehistoric Diplomystus fish fossil from a quarry near Kemmerer, Wyoming. It's from the Green River Formation and approximately 45-50 million years old. It displays well on the included acrylic display stand.

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.

SPECIES Diplomystus dentatus
AGE Eocene (45-50 MYA) View on Geological Time Scale
LOCATION Kemmerer, Wyoming
FORMATION Green River Formation
SIZE 6.25" long on 7.5" x 3" lime rock
CATEGORY Fish Fossils
SUB CATEGORY Green River Fossil Fish