Thanks to the movie Jurassic Park, people identify the Jurassic period, more than any other geological time span, with the age of dinosaurs. The Jurassic is when the first gigantic sauropod and theropod dinosaurs appeared on the earth, a far cry from their slender, man-sized ancestors of the preceding Triassic period. But the fact is that dinosaur diversity reached its peak in the ensuing Cretaceous period, no matter how clunky "Cretaceous Park" sounds as a summer blockbuster!
Geography and climate The Jurassic period witnessed the breakup of the Pangaean supercontinent into two big pieces, Gondwana in the south (corresponding to modern-day Africa, South America, Australia and Antarctica) and Laurasia in the north (Eurasia and North America), as well as the formation of intra-continental lakes and rivers that opened new evolutionary niches for aquatic and terrestrial life. 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, which helps explain the evolution of the earliest, armor-bearing ankylosaurs and stegosaurs.
Mammals. The mouse-sized early mammals of the Jurassic period, only recently evolved from their Triassic ancestors, kept a low profile, scurrying around at night or nesting high up in trees so as not to get squashed under the feet of bigger dinosaurs. Elsewhere, the first feathered dinosaurs began to appear, typified by the extremely bird-like 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; most paleontologists believe that modern birds descend from the small, feathered theropods of the Cretaceous period.
Marine Life During the Jurassic PeriodJust 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 plesiosaurs like Elasmosaurus (ichthyosaurs, which dominated the Triassic period, had already begun their decline). Prehistoric fish were abundant, as were squids and sharks, providing a steady source of nourishment for these and other marine reptiles.
Avian Life During the Jurassic Period
By the end of the Jurassic period, 150 million years ago, the skies were filled with relatively advanced pterosaurs like Pterodactylus, Pteranodon and Dimorphodon. As detailed above, prehistoric birds had yet to fully evolve, leaving the skies firmly under the sway of these avian reptiles (with the exception of some pesky, buzzing prehistoric insects).
Plant Life During the Jurassic Period
Gigantic plant-eating sauropods like Barosaurus and Apatosaurus couldn’t have evolved if they didn’t have a reliable source of food: hence the landmasses of the Jurassic period were blanketed with thick, tasty coats of vegetation, including ferns, conifers, cycads, club mosses and horsetails. Flowering plants continued their slow and steady evolution, culminating in the explosion that helped fuel dinosaur diversity during the ensuing Cretaceous period.
Next Page: The Cretaceous Period