Fossil fish, Diplomystus, Wyoming #4
Fossil fish, Diplomystus, Wyoming #4
Fossil fish, Diplomystus, Wyoming #4
Fossil fish, Diplomystus, Wyoming #4

Fossil fish, Diplomystus, Wyoming #4

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Age: Eocene Epoch

Location: Self-collected in Kremmerer, Wyoming at The America Fossil Quarry (

Species: Diplomystus dentatus 

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.

The Diplomystus dentatus, was a large predator, up to 26", but most you will find are juveniles, common up to 6" or so.

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.