The climate was hot and humid, with steady rainfall, ideal conditions for the explosive spread of lush, green plants.Terrestrial Life During the Jurassic Period Dinosaurs: During the Jurassic period, relatives of the small, quadrupedal, plant-eating prosauropods of the Triassic period gradually evolved into multi-ton sauropods like Brachiosaurus and Diplodocus.This period also saw the concurrent rise of medium- to large-sized theropod dinosaurs like Allosaurus and Megalosaurus.
At about the same time, intra-continental lakes and rivers formed that opened new evolutionary niches for aquatic and terrestrial life.
Marine Life During the Triassic Period Because the Permian Extinction depopulated the world's oceans, the Triassic period was ripe for the rise of early marine reptiles.
These included not only unclassifiable, one-off genera like Placodus and Nothosaurus but the very first plesiosaurs and a flourishing breed of "fish lizards," the ichthyosaurs.
For reasons that are still unclear, the archosaurs held the evolutionary edge, muscling out their "mammal-like" cousins and evolving by the middle Triassic into the first true dinosaurs like Eoraptor and Herrerasaurus.
Some archosaurs, however, went in a different direction, branching out to become the first pterosaurs (Eudimorphodon being a good example) and a wide variety of ancestral crocodiles, some of them two-legged vegetarians.