Fish Fossil (Knightia Eocaenc)

Vertebrates date back to the Devonian period, about 48 million years ago. These vertebrates have internal skeletons and represent some of the most interesting organisms in fossil record. Fish fossils like the Knightia (shown above) are one of the oldest vertebrates, they first appeared in freshwater environments but the spread rapidly from lakes, to rivers and finally to the sea. Many fish fossil such as this herring like Knightia are found in the shale of The Green River formation in Colorado, Utah, and Wyoming.