Wonderfully preserved fossil fish from Wyoming, Priscacara and Knightia alta

A fossil plate with two perfectly preserved fossilized fish, Priscacara and Knightia alta, recovered from the Green River Formation in Wyoming. The fish are embedded in a light limestone matrix, each scale and vertebra sharply defined.

The Green River Formation is one of the most famous fossil sites in the world. In an Eocene lake approximately 50 million years ago, fish sank into oxygen-poor bottom waters, where they were covered by fine carbonate muds without scavenger activity—a perfect preservation environment.

Knightia alta is the most common herring species in the formation, while Priscacara is a more robust perch relative.

Today, preparation is usually done by splitting the thinly layered platy limestones and careful needlework under a microscope. Visible vertebrae, fin rays, and scales, such as on this piece, are the result of hours of manual excavation.