Diplomystus is an extinct genus of prehistoric fish. Famous for their fossils in the Green River Formation, other members of this genus can be found in 80 million year old marine deposits in South America and Lebanon. The largest Diplomystus found is 26 inches (65cm) long. Diplomystus sported an upturned mouth making this fish a surface feeder. During life, these predatory fish fed on smaller Knightia. Occasionally, Knightia fossils can be found lodged in the throats of large Diplomystus specimens. Fossils are common in certain regions of the formation but are very rare in others. Currently in the Green River Formation, there is only one described species of this genus. However, there have been three other species that have once been named throughout the years. Diplomystus dentatus was onc