<P> The Early Triassic was between about 252 million to 247 million years ago and was dominated by deserts as Pangaea had not yet broken up, thus the interior was nothing but arid . The Earth had just witnessed a massive die - off in which 95% of all life became extinct . The most common vertebrate life on earth were Lystrosaurus, labyrinthodonts, and Euparkeria along with many other creatures that managed to survive the Great Dying . Temnospondyls evolved during this time and would be the dominant predator for much of the Triassic . </P> <P> The Middle Triassic spans roughly from 247 million to 237 million years ago . The Middle Triassic featured the beginnings of the breakup of Pangaea, and the opening of the Tethys Sea . The ecosystem had recovered from the devastation that was the Great Dying . Algae, sponge, corals, and crustaceans all had recovered, and the reptiles began to get bigger and bigger . New aquatic reptiles evolved, such as ichthyosaurs and nothosaurs . Meanwhile, on land, pine forests flourished, as did groups of insects like mosquitoes and fruit flies . The first ancient crocodilians evolved, which sparked competition with the large amphibians that had since ruled the freshwater world . </P> <P> The Late Triassic spans roughly from 237 million to 201 million years ago . Following the bloom of the Middle Triassic, the Late Triassic featured frequent heat spells, as well as moderate precipitation (10 - 20 inches per year). The recent warming led to a boom of reptilian evolution on land as the first true dinosaurs evolved, as well as pterosaurs . During the Late Triassic, some advanced cynodonts gave rise to the first Mammaliaformes . All this climatic change, however, resulted in a large die - out known as the Triassic - Jurassic extinction event, in which many archosaurs (excluding pterosaurs, dinosaurs and crocodylomorphs), most synapsids, and almost all large amphibians became extinct, as well as 34% of marine life in the fourth mass extinction event of the world . The cause is debatable . </P> <P> The Jurassic ranges from 200 million years to 145 million years ago and features 3 major epochs: The Early Jurassic, the Middle Jurassic, and the Late Jurassic . </P>

What is the oldest period in the mesozoic era