45-50 million year old fossil
These fish are between 45 and 50 million years old and come from the Wyoming region in the USA. In the Eocene there was a vast lake that was home to a lot of life. Due to rainy and dry periods, a layer of sediment was added to the bottom of the lake every year. 6 million years of continuous sediment has been found.
Fish and sometimes other animals could be preserved between the sediment. The sedimentary seal prevented the carcass from decomposing and allowed it to fossilize. Wyoming is known for its great diversity of fossils and the high quality in which they are preserved.