Climate and Geography The Jurassic period witnessed the breakup of the Pangaean supercontinent into two big pieces, Gondwana in the south and Laurasia in the north, as well as the formation of intra-continental lakes and rivers that opened new evolutionary niches for aquatic and terrestrial animals. 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, relatives of the small, quadrupedal, plant-eating prosauropods of the Triassic period gradually evolved into gigantic sauropods like Brachiosaurus and Diplodocus. This period also saw the rise of medium- to large-sized theropod dinosaurs like Allosaurus and Megalosaurus, which helps explain the evolution of the earliest ankylosaurs (armored herbivorous dinosaurs). The Jurassic period was also the heyday of the stegosaurs, typified by Stegosaurus.
The first, mouse-sized early mammals of the Jurassic period kept a low profile, scurrying around at night so as not to get squashed under the feet of bigger dinosaurs. Elsewhere, the first small theropod dinosaurs began to evolve feathers, culminating in Archaeopteryx and Epidendrosaurus. It's possible that the first true prehistoric birds had evolved by the end of the Jurassic period, though the evidence is still sparse.
Marine Life Just as dinosaurs grew to bigger and bigger sizes on land, so the marine reptiles of the Jurassic period gradually attained shark- (or even whale-) sized proportions. The Jurassic seas were filled with fierce pliosaurs like Liopleurodon and Cryptoclidus, as well as sleeker, less frightening swimmers like Plesiosaurus. Prehistoric fish were abundant, as were squids and prehistoric sharks, providing a steady source of nourishment for these and other marine reptiles.
Avian Life By the end of the Jurassic period, the skies were filled with relatively advanced pterosaurs like Pterodactylus, Pteranodon and Dimorphodon. As stated above, prehistoric birds had yet to fully evolve, leaving the skies firmly under the sway of these avian reptiles (with the exception of some prehistoric insects).
Plant Life Gigantic herbivorous dinosaurs like Barosaurus and Apatosaurus couldn’t have evolved if they didn’t have a reliable source of food: the landmasses of the Jurassic period were blanketed with thick, tasty coats of vegetation, including ferns, conifers, cycads, club mosses and horsetails.
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