Triassic
The first part of the Triassic had much less variety than the Permian, and showed signs of a deteriorated environment. This situation lasted for about five million years, then steadily improved. Into the vacant ecological niches, new forms evolved, replacing old with new. This rapid adaptive radiation happened to the reptiles on land, the fish in the seas, and a number of other groups, like the insects. Communities with complex ecology took 30 million years to re-establish.