Evolution of Fish

Abstract

Ostracoderms: The first fishes, and indeed the first vertebrates, were the ostracoderms, jawless fishes found mainly in fresh water. They were covered with a bony armor or scales and were often less than 30 cm (1 ft) long. The ostracoderms are placed in the class Agnatha along with the living jawless fishes, the lampreys and hagfishes, which are believed to be descended from the ostracoderms. Cambrian to Devonian