''Diplomystus'' is an extinct genus of freshwater clupeomorph fish distantly related to modern-day extant herrings, alewives, and sardines. The genus was first named and described by

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...

in 1877. There are seven species of ''Diplomystus'': ''D. dentatus'' (Cope, 1877), ''D. birdii'', ''D. dubetreiti'', ''D. shengliensis'' (Chang 1983), ''D. kokuraensis'' (Uyeno 1979), ''D. primotinus'' (Uyeno 1979), and ''D. altiformis''. ''Diplomystus dentatus'' (Cope, 1877) is well known from lower

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

deposits from the

Green River Formation The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine ...

in Wyoming. Specimens range from larval size to 65 cm and are commonly found in close association with the extinct herring ''

Knightia ''Knightia'' is an extinct genus of clupeid bony fish that lived in the freshwater lakes and rivers of North America and Asia during the Eocene epoch. The genus was erected by David Starr Jordan in 1907, in honor of the late University of Wyom ...

sp.'' The Green River Formation is the remnant of a large lake whose mud would eventually be transformed into soft calcite-bearing shale. ''D. kokuraensis'' (Uyeno 1979), ''D. primotinus'' (Uyeno 1979), and ''D. altiformis'' were dominant members of an Early Cretaceous lake fauna (the "''Diplomystus''-''Wakinoichthys'' Fauna") in what is now Japan and Korea.

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Bibliography

* * * Prehistoric ray-finned fish genera Clupeiformes Cretaceous bony fish Eocene fish Priabonian genus extinctions Prehistoric fish of North America Natural history of Wyoming Early Cretaceous fish of Asia Valanginian genus first appearances Freshwater fish {{clupeiformes-stub