These fish are from the Green River Formation of southwest Wyoming in an area known as Fossil Lake. A rare place where the conditions were right for a rich accumulation of undisturbed fossils that are complete and detailed. Fish fossils of Diplomystus and Knightia fish are found in this fine-grained lime mud that date over 48 million years, covering the early Eocene era to the mid-Eocene era. The Green River Formation was discovered by missionaries and explorers in 1840’s and the first fish fossil was collected in 1856 by Geologist Dr. John Evans. The Smithsonian Institute has a collection of more than twenty-two orders of insect from this formation on display in Washington D.C.