Juvenile Green River Fossil Fish Phareodus encaustus

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. This is a most uncommon juvenile example, the smallest I have seen to date.

The genus Phareodus is uncommon in the Green River formation and is readily distinguished by the long pectoral fin (here prominantly splayed) and large pointed teeth. There are two species: encaustus and testis, of which encaustus is the larger by nearly a factor of two with a maximum size of 75 cm. Other differences are to be found in the body outline, fine ray count, and scale row number. Phareodus sports teeth that are testament to the fish’s carnivorous habit. In fact, the genus name means "to have tooth", with a higher tooth count also found in P. encaustus. A member of family Osteoglossidae (bony-tongues), it has extant cousins found in Central-South America and Southeast Asia, known as the Arrowana and Arapaima. The genus is known from the Eocene deposits of North America and Australia.