Name Meaning: Double Whiskers
Location Found: Wyoming
Geologic Era: Eocene
Estimated Range: Western United States and Canada, Japan, Italy, Korea
Size: Up to 65 cm in length
Extinction Date: 34 million years ago
Diplomystus is one of the more common fish found in the Green River Formation. It is related to the modern herring, and was probably an open water predator that hunted at or near the surface of the water. Our specimen is on the smaller end of the spectrum for the species at about 12 centimeters long. It was probably relatively young when it died, as it is closer in size to fossilized Diplomystus fry than to the truly larger individuals. There is fossil evidence of Diplomystus preying on Knightia fish, another common animal found in the Green River Formation. Such attempts at predation did not always end well for the Diplomystus, as a few specimens have been found with the Knightia stuck halfway down the Diplomystus’ throat.
The reason for the commonality (and beautiful preservation) of Green River fish is the environmental conditions that were linked to the mass die-offs. Just like in modern ponds and lakes, algae will occasionally take over bodies of water, effectively suffocating the fish in the lake or pond. These fish would sink to the bottom, and become buried in mud rather quickly. Quick burial allowed for some level of soft tissue preservation, as seen with Diplomystus fry.