Green River Formation Fish Fossil Aspiration

Mioplosus eating Knightia

Mioplosus labracoides

Class Actinopterygii, Order Perciformes, Family Percidae

Knightia eocaena

Class Actinopterygii, Order Clupeifomes; Family Clupeidae

Geological Time: Eocene

Size: Fish fossil is 150mm Mioplosus: 135 mm in length on a 200 mm by 105 mm matrix.

Fossil Site: 18 Inch Layer Green River Formation, Fossil Lake, Kemmerer, Wyoming

Code: WFF161

Price: Sold

Description: This 50 million year old, Eocene-Era fossil fish comes from one of the world's famous Laggerstatten, the Green River Formation in Wyoming. A small portion of the fish fossils from Green River exhibits such fine preservation. The significant extent of soft-tissue preservation that makes the site famous is evident in this specimen. The rich brown color shows this one comes from the famous 18 Inch Layer, a name derived from the thickness of the deposits from which these excellent specimens are quarried.

This one is known as an “aspiration”, a name given such specimens in that the fish died while choking on its prey, here a small Knightia. A few specimens such as this are found each year, and are highly prized by collectors. I was fortunate to acquire this one and one other at this year’s Tucson fossil show.

Mioplosus labracoides is believed to have been a voracious predator among the Green River fish fossils. Failure to find its numbers in mass mortality leads to further conjecture that it was a solitary hunter. A member of the Family Percidae, it has numerous relatives in Northern Hemisphere fresh water as well as fossil relatives in Asia, Europe and New Zealand. It is known as a predatory species as determined from its many pointed teeth, and the fact that several have been found with fish lodged in its throat, just as this one. It may be related to the modern-day pike of the genus Stezostedion.

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