The Mesezoic Era (middle life) is an era that lasted from 250 to 65 million years ago (mya). It is the most famous of all because it was the time of the dinosaurs. It was just one of three eras that made up the Phanerozoic Eon. The Mesezoic began just after the Permian Extinction, the biggest extinction of all. The only group to have survived were the dictodonts such as Lystrosaurus. As they evolved into more and more species, the world came back to life. The first Mesezoic period was the Triassic Period. In the early Triassic, there were few animals because the recent extinction. But soon a very important evelutionary event happened: there were the first mammals. But by the middle Triassic, dinsaurs had appeared, and by the late Triassic dinosaurs were thriving. In the oceans there were repiles too, such as icthiosaurs. A flying group called the perosaurs had evolved, too. The next period was the Jurassic Period, when dinosaurs and marine reptiles grew huge. By the Cretaceous Period, dinosaurs flourished until the Cretaceous Extinction, wiped out all marine reptiles, pterosaurs, and non-avian dinosaurs and ended the Mesozoic Era.