Reptiles remain the dominant land animals even after their massive losses to extinction at the end of the Triassic. Dinosaurs grow larger, with the largest saurichians appearing in the Upper Jurassic. The other main dinosaur group, the ornithicians, makes their first appearance in the Jurassic. The first birds show up in the fossil record, but flying pterosaurs of all sizes rule the air. Theropod dinosaurs, which gave rise to birds, continue to evolve in parallel—both groups are covered in colorful feathers.
Insect diversify, evolving many modern forms such as wasps and beetles. The first lizards appear, probably feeding on the new insect diversity. Conifers dominate coal-producing forests. Forests covered much of the land, with trees such as conifers, gingko, and an under story of plants such as ferns, cycads and horsetail rushes. Flowering plants had yet to evolve and there were no grasses so the open plains of modern Earth did not exist making it a very different world than today.
The supercontinent Pangaea begins breaking up during the Jurassic, with the birth of the Central Atlantic Ocean at the end of the Middle Jurassic. Sea levels start low, becoming high by the Middle Jurassic.
Most of today's continental outlines are delineated by the end of the Jurassic, though they are not in their current locations.
Pangea and what became North America, was located equatorially for most of the Jurassic. Earth experienced a warm, moist greenhouse climate, especially in the late Jurassic, when much of the world was lush and tropical. Although the trilobites had vanished in the Permian extinction event, the arthopods were well represented in the oceans by crustaceans.
These included shrimp, lobsters, and crabs such as Eryon. Eryon arctiformis. Brittle stars Ophiuroidea are represented by specimens of Geocoma elegans on a rock slab. Geocoma elegans. Sea urchins Echinoidea diversified during the Jurassic. Just as hours divide into minutes, eras divide into periods. The first period of the Mesozoic Era was the Triassic Period. It began In the case of the Jurassic Period, that layer of rock is a layer of limestone in the Jura Mountains. The Jura Mountains are located on the France-Switzerland border.
It is from this mountain range that the Jurassic Period gets its name. There are three distinct bands in the main limestone layer. Some consider the predators that preyed on these giants to be even more spectacular. For example, Tyrannosaurus rex is so well-known that it seems to be one of the first tongue twisters that children master. Modern research has disproved the old concept that dinosaurs were slow-moving, dim-witted, solitary creatures, forced to wade about in swamps because their great bulk could not be supported on land.
In fact, many dinosaurs were very agile even the large ones. Many species apparently roamed the land easily despite their size, and some were quite social, traveling in herds, building nests, and caring for their young Macdougall With the discovery of many new species since the s, scientists have divided the Dinosauria into two major groups: the Ornithischia and the Saurischia, with the distinction based on the construction of the pelvis.
Some of the quadrupedal saurischians developed into the largest land animals in history, including Diplodocus perhaps reaching lengths of feet [30 m] or more and Brachiosaurus perhaps weighing as much as , pounds [60, kg]. In H. Seeley introduced the division between the two groups. However, birds are descendants of saurischians, specifically theropods. First birds. The first flying vertebrates were true reptiles in which one of the fingers of each front limb became elongated, providing support for a flap of stretched skin that served as a wing.
In the Jurassic another flying group took to the air—birds—which evolved quite separately from the pterosaurs. Birds and pterosaurs serve as an example of a common theme in evolution, the parallel development of different types of body structures and function for the same reason, in this case for flight.
The evolution of flight led to generally light and fragile skeletons, so not surprisingly, avian fossils are uncommon, and when found, often fragmentary. Palm tree-like cycads were abundant, as were conifers such as araucaria and pines. Ginkgoes carpeted the mid- to high northern latitudes, and podocarps, a type of conifer, were particularly successful south of the Equator. Tree ferns were also present. The oceans , especially the newly formed shallow interior seas, teemed with diverse and abundant life.
At the top of the food chain were the long-necked and paddle-finned plesiosaurs, giant marine crocodiles, sharks, and rays. Fishlike ichthyosaurs, squidlike cephalopods, and coil-shelled ammonites were abundant. Coral reefs grew in the warm waters, and sponges, snails, and mollusks flourished.
Microscopic, free-floating plankton proliferated and may have turned parts of the ocean red. On land, dinosaurs were making their mark in a big way—literally. The plant-eating sauropod Brachiosaurus stood up to 52 feet 16 meters tall, stretched some 85 feet 26 meters long, and weighed more than 80 tons.
Diplodocus , another sauropod, was 90 feet 27 meters long. These dinosaurs' sheer size may have deterred attack from Allosaurus , a bulky, meat-eating dinosaur that walked on two powerful legs. But Allosaurus and other fleet-footed carnivores, such as the coelurosaurs, must have had occasional success. Other prey included the heavily armored stegosaurs. The earliest known bird, Archaeopteryx , took to the skies in the late Jurassic, most likely evolved from an early coelurosaurian dinosaur.
Archaeopteryx had to compete for airspace with pterosaurs, flying reptiles that had been buzzing the skies since the late Triassic. Meanwhile, insects such as leafhoppers and beetles were abundant, and many of Earth's earliest mammals scurried around dinosaur feet—ignorant that their kind would come to dominate Earth once the dinosaurs were wiped out at the end of the Cretaceous.
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