Diplomystus Fossil Fish, from Green River Formation, Wyoming, U.S.A. (REF:DIPF4)

Diplomystus is an extinct genus of freshwater non-clupeoid clupeomorph fish distantly related to modern-day extant herrings, alewives, and sardines. The genus was first named and described by Edward Drinker Cope in 1877.

D. dentatus (Cope, 1877) is well known from lower Eocene deposits from the Green River Formation in Wyoming. It had a moderately deep body, a homocercal tail, single dorsal and anal fins, and a pelvic fin sited directly beneath the dorsal fin. The scales are thin and ovoid. The strongly upturned mouth is typical of a surface-water feeder.