Evolution from Fish to Land Animals (Devonian Fish)
8The earliest fish had no jaws and fed mainly on small organisms. Some of these primitive fish developed jaws, which enabled the mouth to open and shut to bite. They hunted other animals and became the top marine predators of primitive times. The key groups of jawed fish are: Armored fish (extinct); Acanthodians (extinct); Cartilaginous fish (sharks) and Bony fish (most modern fish).
Devonian marine life mainly consisted of shellfish, corals, trilobites, sea lilies, nautiloids, and sea scorpions. Fish were at the top end of the food chain. The Devonian fishes were the ones that evolved into land animals. This was during the paleozoic era.
In the late Devonian (approximately 360 million years ago), the Earth's environment changed drastically. The land area expanded, and the area of shallow seas shrank, resulting in extensive coastal marshes. Some arthropods (like insects) and fish gradually adapted to these marshes, which often dried out. They became the first inhabitants of land.