Central period of the Mesozoic
era, lasting from 213 to 144 million years ago. In this period there were saurischian and ornithischian dinosaurs
, such as Allosaurus and Stegosaurus, plesiosaurs, pterosaurs and archaeopteryx
. Primitive mammals had begun to evolve.
Allosaurus, late Jurassic carnivorous dinosaur of the W United States. Specimens of 30 to 40 ft (9 to 12 m) have been found. It had stong hind legs, smaller sharply clawed forelimbs, two small horns directly above the eyes, and expandable jaws that could widen to consume large pieces of meat.