Fish

Fishes

Fishes were among the first vertebrates to evolve. The earliest known fishes were the ostracoderms, a now-extinct group of jawless fishes that appeared in the Cambrian Period, about 510 million years ago. Other early fish include the conodonts and the agnanthans (the hagfish and the lamprey). Fishes later evolved jaws and diversified into a number of lineages including cartilaginous fishes, ray-finned fishes and lobe-finned fishes.

The ray-finned fishes are the most diverse of all vertebrate groups, with some 24,000 species. There are about 810 species of cartilaginous fishes and 8 species of lobe-finned fishes.