From the Green Wyoming River in the United States. In the Green River Formation, the fossils span a five million year period. Roughly 53.5 million and 48.5 million years old. The preservation of so many fossils is probably due to both a cold period that made dead fish sink faster due to their deflated swim bladders and the depth and conditions that kept scavengers away.
These fish fossils are currently sold by the unique piece. You will get the piece pictured.