Fish are one of the most diverse groups of vertebrates to have existed on Earth. The first fish evolved in the Cambrian over 490 Million years ago and they are still abundant today. The Devonian period is often called the Age of the Fishes.
Sharks are one of the major groups of marine vertebrates that existed on Earth for over 400 million years upto the present day. The cartilaginous skeletons of sharks do not normally fossilize very well but their fossil teeth can be very abundant.