12-1/8x15.75x.5" thick, superb specimen contains the complete fossilized remains of seven Knightia fish, each measuring between 3.5" and 4.5" long. The edge of the specimen also contains a partial fossil of another small fish. Knightia is an extinct genus of bony fish related to modern day herrings and sardines which lived in North American freshwater lakes and rivers during the Eocene epoch. The specimen came from the Lower Eocene (55 million years old) deposits of the Green River Formation in Wyoming. The fish fossils from the Green River Formation are considered the best preserved fish fossils ever found. During the Eocene, large inland seas covered much of what is now the Western United States. The most well-preserved Eocene fish fossils come from this region. The example we are offering is nicely preserved, w/many of the vertebrae present, each fish's outline distinct.