Middle and Late Jurassic Periods
By the Middle and Late Jurassic, dinosaurs had taken over the world. There were herds of Apatosaurus; each adult was as large as five or six elephants. Allosaurus, a two-ton meat-eater, waited in the bushes for its next meal; it needed to eat often to fill its appetite. Bony plates protected slow, steady Stegosaurus, which had little fear of predators. The land quaked with dinosaur footsteps. Dinosaurs controlled this Jurassic world.
Canadian Museum of Nature
Pangaea continued to break apart in the Jurassic. It was splitting both north and south, and east and west. The land masses were beginning to resemble the shapes they have today. The Tethys Sea separated the southern land mass, called Gondwanaland, from the northern mass, called Laurasia. Laurasia consisted of North America, Europe, and Asia. Sometimes, probably because of sea level changes, it's likely there were land connections between Gondwanaland and Laurasia. Dinosaurs were very similar in North America and eastern Africa in the Late Jurassic. The Atlantic Ocean was still very narrow, and there was probably a land bridge that allowed the dinosaurs to migrate between the two continents.
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The northern part of the Atlantic Ocean began to open during the Jurassic, and it separated Laurasia into eastern (Europe and Asia) and western (North America) land masses. There were probably land bridges that connected these two land masses across the north when the sea level dropped. Antarctica gradually broke away from Gondwanaland and was over the South Pole by the Early Cretaceous. The continents were drifting apart at a rate of about a quarter of an inch to three inches a year (which is about as fast as a human fingernail grows).
All these changes in the continents changed the way the ocean waters flowed. Cold ocean currents in the southern hemisphere produced temperate climates in what is now South America, southern Africa, Antarctica, India (an island off eastern Africa), and Australia. The rest of the world was also warm and moist, and the Triassic deserts were shrinking and were gone by the Late Jurassic. There were no polar ice caps.
In this dry and semi-dry Jurassic landscape, conifers dominated wherever trees grew. Except for dinosaurs, the Jurassic plants and animals were much like those of earlier times. There were many ferns, tree ferns, cycads, ginkgos, and horsetails. Grasses had not yet evolved, but some ferns may have served as low ground cover.