Diplomystus Dentatus Fish Fossil
Green River Formation, Wyoming
Eocene age (56 Million years ago)
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 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. D. dentatus (Cope, 1877) is well known from lower Eocene deposits from the Green River Formation in Wyoming. Specimens range from larval size to 65 cm and are commonly found in close association with the extinct herring Knightia 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. Dimensions: 4.6 Inches Long & 3 Inches Wide (Plate) Fish is 4.2 Inches Long & 1.5 Inch Wide. Diplomystus Dentatus morphology, including its upturned mouth, is prototypic of a surface feeding fish. The genus is herrings that likely fed on small surface-dwelling fish as Knightia is evidenced by numerous fossils found with Knightia is the stomach or mouth. The unusual chemistry of fossil lake prevented decay and scavenging of dead organisms while millimeter-thick layers of alternating limestone matter slowly accumulated. The result is laminated limestones that contained the highest concentration of fossil fish in the world. These fish, other aquatic organisms, and associated geologic features make Fossil Lake the world's best Paleogene record of the freshwater lake ecosystem.