Advertisement

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.

Apatosaurus
Canadian Museum of Nature
Apatosaurus was a sauropod that came to dominance in the Jurassic

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.

Get to know the Middle and Late Jurassic dinosaurs.
Check out these individual profiles:


Allosaurus Kentrosaurus

Apatosaurus Mamenchisaurus

Archaepteryx Megalosaurus

Brachiosaurus Omeisaurus

Camarasaurus Ornitholestes

Camptosaurus Othnielia

Ceratosaurus Patagosaurus

Cetiosaurus Seismosaurus

Chungkingosaurus Shunosaurus

Compsognathus Stegosaurus

Dacentrurus Supersaurus

Datousaurus Tuojiangosaurus

Diplodocus Ultrasaurus

Dryosaurus Xuanhanosaurus

Euhelopus Yandusaurus

Huayangosaurus Yangchuanosaurus

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.

Advertisement

Advertisement

Pterosaurs glided and flapped their way to feeding grounds. There were two types of pterosaurs, ones with tails and ones without. The pterosaurs with tails did not last past the Late Jurassic; the pterosaurs without tails survived into the Cretaceous. Crocodiles, which replaced the phytosaurs of the Triassic, lurked in the undergrowth near water. Mammals, the descendants of the therapsids, were still running around. They were mostly shrewlike creatures that were four to five inches long, eating insects or chewing fruits and seeds. New insects were also evolving, including the ancestors of earwigs, flies, and bees, among others.

Jurassic Map
Collection of Publications International, Ltd.
Jurassic Map

The mammallike reptiles that were so important in the Triassic were gone by the Middle Jurassic, as were the rauisuchids and other archosaurs. Late in the Jurassic, small lizards, frogs, and salamanders crawled around under the cover of plants. Turtles, though not large, had also appeared. In the seas, corals, clams, and snails flourished, as did sharks and the marine reptiles, including plesiosaurs and ichthyosaurs.

This landscape provided food, forage, and home for the dinosaurs. As the land became greener in the Late Jurassic, the sauropods gained the advantage. They reached from China to North America to Africa. From the earliest sauropods in the Early and Middle Jurassic, and the carnivores that evolved with them, arose the giants of the Late Jurassic. Apatosaurus, Diplodocus, Brachiosaurus, Ultrasaurus, Supersaurus, Allosaurus, and Ceratosaurus roamed the earth. Others, like the ornithopods Stegosaurus and Camptosaurus, survived the great deserts of the Middle Jurassic and added to the growing group of dinosaurs. Late Jurassic dinosaurs were spectacular. They exceeded the imagination in size and form.

Advertisement

Advertisement

The large plant-eaters such as Apatosaurus moved constantly, perhaps like elephants feeding almost around the clock. They probably destroyed plant life as they grazed through an area, but at the same time they opened the ground to more sunlight for new growth. Migration of the sauropods was random and only loosely tied to a region. They may have had separate areas for laying eggs, where the young would hatch away from the adults. The large herds probably were mostly adults, with the adults protecting the young.

The large sauropods browsed at the tops of trees for food, where no other dinosaurs could reach. The smaller plant-eaters ate ground cover and shorter brush. Some, such as Stegoceres, probably reared up on their hind legs to get higher brush. The small meat-eaters probably ate lizards and scavenged meals from other animals. Large meat-eaters would have eaten smaller dinosaurs and even attempted to kill a sauropod, perhaps a youngster that strayed from the herd.

Dinosaurs of the Late Jurassic in China showed general similarities of body to those in other parts of the world. There were sauropods, stegosaurs, carnosaurs, and coelurosaurs, but when we look carefully, we see that the Chinese forms were all unique. They were not found in Africa or North America. China seems to have been isolated from the rest of the world at this time.

Archaeopteryx flew from conifer tree to conifer tree. It was an ancestor of modern birds. A coelurosaur dinosaur of the Middle Jurassic may have been its ancestor.

More and more kinds of dinosaurs were evolving in the Middle and Late Jurassic Period, but the most important dinosaurs of this time were the sauropods. These immense creatures roamed the earth searching for food to sustain their enormous size. The earth did provide for them, though there are still some questions scientists have about their diets. These animals were the most successful dinosaurs, with their numbers growing rapidly. They were truly the masters of their universe.

Advertisement

Advertisement

Advertisement


Advertisement

Advertisement

Advertisement

Advertisement

Advertisement

Advertisement