Permian Life Forms
During the Permian Epoch, in the latter stages of the Paleozoic Era, fish became much
more diverse and included armoured species, lungfish, sharks, and fringe-finned fish.
Thought to have appeared in the depths of large muddy lakes, fish began to move
into streams and toward the seas, where they would have to adapt to completely new
conditions.

Source: Ellis Owen, Prehistoric Animals