A single well preserved fresh water herring fossil, from the Green River Formation in Kemmerer, Wyoming USA. This fossil is dated approximately 55 million years old.
Fish are relatively rare as fossils; the fragile nature of a fish body makes it a poor candidate for fossilization. However, there are some unique environments and circumstances that existed in prehistory where some deposits in the world produce the most impressive and perfectly preserved fossils known to science. The Green River Formation of southwest Wyoming is one such location.