Priscacara serrata Green River Fossil Fish

Priscacara serrata

Order Perciformes, Family Priscacaridae

Geological Time: Eocene

Size: Priscacara fish fossil 150 mm in length

Fossil Site: Green River Formation, Fossil Lake, Kemmerer, Wyoming

PriscacaraDescription: These 50 million year old, Eocene-Era fossil fish come 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.

Genus Priscacara is perhaps the most popular of the Green River fish fossils. A member of the Family Priscacaridae, the name Priscacara means "primitive head". Shaped rather like a sunfish, the genus sports sturdy, protective dorsal and anal spines. Among the two species, liops and serrata, serrata is uncommon. The species name comes from the diagnostic serrated preopercle, seen here in closeup. Liops is the smaller species, never exceeding 150 mm, whereas serrata have been found up to 375 mm. The genus went extinct at the end of the Miocene, and is thought by some to be related to the modern-day Cichildae.

The smaller fish is Knightia eocaena, the State Fossil of Wyoming. In Fossil Lake, these fish reach their maximum size of 25 cm, but averages roughly half that. Knightia was a schooling fish which is sometimes found in mass mortality layers confined to a single plane, indicative of a single event. The one seen here would have served as a prey species for the Priscacara which just overlies it, showing that while they were contemporaries, the Knightia fell to the lake bottom just before it, making them prisoners in time for the past 50 million years.

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