The Jurassic period was in the middle of the Age of Reptiles, with major dinosaur groups evolving in the Late Triassic. The landscape was dominated by conifers, cycads, and ferns, and the climate was warm and lush. Dinosaurs ruled for 30 million years, with two main groups: saurischians and ornithischians. Large theropods and sauropods dominated, with the largest reaching 12m and 34m in length, respectively. The Jurassic is considered the golden age of sauropods.
The Jurassic period spanned from approximately 200 to 146 million years ago. The Jurassic period was right in the middle of the ‘Age of Reptiles’, also known as the ‘Age of Dinosaurs’. In the Late Triassic, immediately before the Jurassic, almost all major dinosaur groups evolved: theropods (which includes all carnivorous dinosaurs), sauropods (long-necked herbivores that grew to absolutely gigantic sizes during the Jurassic), and herbivores assorted such as Stegosaurus. Other non-dinosaur reptiles had also evolved in the Late Triassic, including pliosaurs (marine reptiles) and pterosaurs (large winged reptiles).
The Jurassic was immediately before the age of flowering plants, so the landscape was dominated by conifers, cycads and ferns. Cycads, tropical trees with sturdy trunks, had their greatest success during the Jurassic period, and even today many intuitively recognize these plants as “common in the time of the dinosaurs”. Unlike the arid Triassic before it, or the cold Cenozoic today, the Jurassic was lush and warm, even at higher elevations, where forests stretched all the way to the poles. This climate was extremely encouraging towards life at that time.
By the early Jurassic, dinosaurs had already ruled the Earth for about 30 million years. There were two main groups: saurischians (dinosaurs with lizard sides) and ornithischians (dinosaurs with bird sides). The saurischians included the theropods (all carnivores) and sauropods (the largest herbivores). Ornithischians included a variety of other medium to large herbivores, though all smaller than most sauropods. Confusingly, birds actually evolved in the Late Jurassic from lizard-pelvis dinosaurs. They acquired a distinctive bird’s hip, in an example of parallel evolution.
Various large theropods dominated Jurassic ecosystems, such as the carnivorous Allosaurus, which had the same body plan as Tyrannosaurus rex, which didn’t evolve until 90 million years later. The largest of this species reached 12 m (39 ft) in length and was among the most terrifying land carnivores of all time. No terrestrial carnivores today even come close.
The Jurassic is considered the golden age of sauropods, huge long-necked dinosaurs that used their height to eat the leaves of the tallest trees. Many sauropods were of such mass and size that they had little to worry about even the largest predators like Allosaurus. A late Jurassic sauropod, Supersaurus, was up to 34 m (112 ft) long and weighed up to 40 tons.
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