Green River Fossil Fish Knightia alta

Knightia alta

Order Clupeifomes, Family Clupeidae

Geological Time: Eocene

Size (25.4 mm = 1 inch): 125 mm in length on 162 mm by 115 mm matrix

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

Knightia altaDescription: 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.

This particular fish is Knightia alta, a close relative of Knightia eocaena. It is a more robust species, and is far less common than K. eocaena in Fossil Lake. At a maximum size of 150 mm, it was just over ½ the size of K. eocaena. Knightia was a schooling fish which is sometimes found in mass mortality layers confined to a single plane, indicative of a single event. Theories as to the reasons include stratified water turnovers as well as poisoning due to blooms of blue-green algae. The modern-day Alewife is known to do so in the Great Lakes of the US. At the top right you can see a single scale of a larger fish, possibly of the genus Priscacara.

click to enlarge

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