During the Jurassic Period, North America lay close to Europe. The Atlantic Ocean, which now separates the two continents, had not yet opened up and there was no land link between North and South America across Central America as there is today. The polar regions—what is now Alaska and Canada—had no ice or snow, even in winter; the climate was far too warm. Forests of conifers such as redwoods and Chile pine (“monkey-puzzle”), along with ginkgos, cycads, tree ferns and horsetails, covered vast areas of North America, providing a great deal of food for the huge Jurassic plant-eating dinosaurs.

Allosaurus

Terror of the late Jurassic was Allosaurus. This massive meat-eater was 11 metres (36 feet) long and weighed about 2 tonnes. Its teeth were bigger than your hands, and it could run faster than a champion human sprinter. Allosaurus may have chased after big prey, such as the 20-tonne sauropod dinosaur, Camarasaurus. Smaller meat-eaters like Ornitholestes may have scavenged on carcasses or hunted for live prey such as lizards, frogs and insects, along with other, smaller dinosaurs.

Morrison Formation

The Morrison Formation is an area of Late Jurassic sedimentary surface rocks in the western United States. Dating from 156 to 147 million years ago, it is the richest source of dinosaur fossils in North America. Much of the vegetation in Jurassic times grew on river floodplains, so most of the dinosaurs lived there too. Hundreds of dinosaur fossils have been discovered in the area, including Allosaurus, Camptosaurus, Ceratosaurus, Ornitholestes, Stegosaurus, the early ankylosaurs Mymoorapelta and Gargoyleosaurus, the ornithopods Camptosaurus and Dryosaurus, and a large number of sauropods, including Diplodocus, Camarasaurus, Brachiosaurus, Apatosaurus and Barosaurus.