Green River Fossil Fish

The Green River Formation is the richest deposit of fish fossils in the world. The Green River Formation stretches for hundreds of miles across WY, CO, & UT, and is over a mile thick. Under catastrophic conditions in the wide, shallow lakes in the Green River region of WY, some 49.6 million years ago, many fish and marine animals met their death, for reasons, which are unclear. Their remains were covered by a fine deposit of calcium carbonate, preserving every delicate outline. Year after year limestone sediments added layers to this protective cover. Through a long fossilization process, the original bones, skin, and scales were replaced with the minerals in the sediment that buried them. The Green River region was sub-tropical to temperate during the Eocene period, based on fossil records.