Erismatopterus

Erismatopterus is an extinct genus of percopsiform fish which lived during the early to middle Eocene epoch and containing the single species Erismatopterus levatus. A report of the genus in sediments of similar age in Washington State have been discredited. Erismatopterus is treated as part of the family Percopsidae, but formerly was the type genus of the extinct family Erismatopteridae. The genus is closely related to Amphiplaga of related lake sediments. Shoaling behavior has been reported from a mass mortality fossil of E. levatus and attributed as a predator-evasion response behavior.

==Distribution== Erismatopterus levatus is known from solitary fossils and mass mortality groups which are compression-impression fossils preserved in layers of soft sedimentary rock. Along with other well preserved fish fossils, the E. levatus specimens are found in several outcrops of the Early to Middle Eocene Green River Formations Lake Gosiute and Lake Uinta. The formation is a group of Late Paleocene to Late Eocene depositional basins in Wyoming, Colorado, and Utah. Of the three paleolakes that comprise the formation, E. levatus seems to have been absent from Fossil Lake. Study of the paleoflora preserved in the formation indicates the lake was around in elevation surrounded by a tropical to subtropical environment that had a distinct dry season.