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The supercontinent Pangaea began to drift apart during the Jurassic Period.

Credit: USGS

The Jurassic Period was the second segment of the Mesozoic Era. It occurred from 199.6 to 145.5 million years ago, following the Triassic Period and preceding the Cretaceous Period.

During the Jurassic Period, the supercontinent Pangaea split apart. The northern half, known as Laurentia, was splitting into landmasses that would eventually form North America and Eurasia, opening basins for the central Atlantic and the Gulf of Mexico. The southern half, Gondwana, was drifting into an eastern segment that would form Antarctica, Madagascar, India and Australia, and a western portion that would form Africa and South America. This rifting, along with generally warmer global temperatures, allowed for diversification and dominance of the reptiles known as dinosaurs.

Plant life

By the Mesozoic Era, living things had evolved the capability of living on the land rather than being confined to the oceans. By the beginning of the Jurassic, plant life had evolved from Bryophytes, the low-growing mosses and liverworts that lacked vascular tissue and were confined to swampy moist areas.

Ferns and gingkoes, complete with roots and vascular tissue to move water and nutrients and a spore system of reproduction, were the dominant plants of the early Jurassic. During the Jurassic, a new method of plant reproduction evolved. Gymnosperms, cone-bearing plants such as conifers, allowed for wind distribution of pollen. This bisexual reproduction allowed for greater genetic combination and by the end of the Jurassic, the gymnosperms were widespread. True flowering plants did not evolve until the Cretaceous.

Age of the dinosaurs

As Steven Spielberg's 1993 film " Jurassic Park" asserts, reptiles were the dominant animal life forms during the Jurassic Period. Reptiles had overcome the evolutionary hurdles of support and reproduction that limited the amphibians. Reptiles had strong ossified skeletons supported by advanced muscular systems for body support and locomotion. Some of the largest animals ever to live were dinosaurs of the Jurassic Period. Reptiles were also capable of laying amniotic eggs, which kept the developing young moist and nourished during gestation. This allowed for the first fully terrestrial animal life cycles.

Sauropods, the "lizard hipped" dinosaurs, were herbivorous quadrupeds with long necks balanced by heavy tails. Many, such as Brachiosaurus, were huge. Some genera obtained lengths greater than 100 feet and weights over 100 tons, making them the largest land animals ever to walk the earth. Their skulls were relatively small, with nostrils carried high near their eyes. Such small skulls meant that they had very small brains as well. Despite the small brains, this group was very successful during the Jurassic Period and had a wide geographic distribution. Sauropod fossils have been found on every continent except Antarctica. Other well known dinosaurs of the Jurassic include the plated Stegosaurus and the flying Pterosaurs.

Carnosaurus means "meat-eating dinosaur." With such large herbivorous prey animals, it makes sense that large predators were also common. Allosaurus was one of the most common Carnosaurs in North America; numerous intact skeletons have been found in the fossil beds of Utah. Allosaurus was superficially similar to the later evolving Tyrannosaurus rex, although cladistic analysis shows them to be only distantly related. Allosaurus was a bit smaller with a longer jaw and heavier forelimbs. They relied on the stronger hind limbs for a running gait, but it is unclear how fast they could move.

Researchers have unearthed a 112-million-year-old mammal jaw in Japan. The jaw shows that mammals from this clade were rapidly evolving traits that would eventually be found in placental mammals. Here, an illustration of what the first placental mammal would have looked like.

Credit: CREDIT: Image courtesy of Carl Buell

It is unlikely to have been common for an Allosaurus to take on a healthy large adult herbivore like a Brachiosaurus or even a Stegosaurus. They were likely opportunistic, consuming young, sick, aged or injured prey. They were probably able to grasp such prey with their heavily muscled forelimbs, tearing it to pieces with large claws and then swallowing the pieces whole.

Early mammals

Dinosaurs may have been the dominant land animals, but they were not alone. Early mammals were mostly very small herbivores or insectivores and were not in competition with the larger reptiles. Adelobasileus, a shrew-like animal, had the differentiated ear and jaw bones of a mammal and dates from the late Triassic.

In August 2011, scientists in China announced discovery of Juramaia. This tiny animal of the mid-Jurassic has caused excitement among scientists because it is clearly a eutherian, an ancestor of placental mammals, indicating that mammals evolved much earlier than previously thought.

Marine life

Marine life of the Jurassic Period was also highly diversified. The largest marine carnivores were the Plesiosaurs. These carnivorous marine reptiles typically had broad bodies and long necks with four flipper shaped limbs. Ichthyosaurus was a more fish-shaped reptile that was most common in the early Jurassic. Because some fossils have been found with smaller individuals that appear to have been inside the larger ones it is hypothesized that these animals may have been among the first to have internal gestation and bear live young. Cephalopod ancestors of modern squid and finned relatives of modern sharks and rays were also common. Among the most beautiful fossils of marine life were left by the spiral shells of the Ammonites.

Editor's note; This article was updated on April 17, 2013, to correct descriptions of life during the Mesozoic Era and of the Juramaia.

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The Jurassic Period was the second segment of the Mesozoic Era. It occurred from 199.6 to 145.5 million years ago, following the Triassic Period and preceding the Cretaceous Period. During the Jurassic Period, the supercontinent Pangaea split apart.

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Dinosaurs, birds, and rodents. Crumbling landmasses and inland seas. Sea monsters, sharks, and blood-red plankton. Forests of ferns, cycads, and conifers. Warm, moist, tropical breezes. This was the Jurassic, which took place 199 to 145 million years ago.

A Shifting Climate and Developing Oceans

At the start of the period, the breakup of the supercontinent Pangaea continued and accelerated. Laurasia, the northern half, broke up into North America and Eurasia. Gondwana, the southern half, began to break up by the mid-Jurassic. The eastern portion-Antarctica, Madagascar, India, and Australia-split from the western half, Africa and South America. New oceans flooded the spaces in between. Mountains rose on the seafloor, pushing sea levels higher and onto the continents.

All this water gave the previously hot and dry climate a humid and drippy subtropical feel. Dry deserts slowly took on a greener hue. 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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Dinosaurs, birds, and rodents. Crumbling landmasses and inland seas. Sea monsters, sharks, and blood-red plankton. Forests of ferns, cycads, and conifers. Warm, moist, tropical breezes. This was the Jurassic, which took place 199 to 145 million years ago. A Shifting Climate and Developing Oceans At the start of the period, the breakup of the supercontinent Pangaea continued and accelerated.

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The first mammals began to evolve. Dinosaurs came before this in the Triassic period but the Jurrasic period is the major "dinosaur

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The Mesozoic Era was a major interval of geologic time. Its position as the second of the three major eras of the Phanerozoic Eon is echoed in its name: mesozoic is derived…

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Under the whole Mesozoic Era all of Earth's continents were joined together. That formed a HUGE continent called Pangea. Pangea was later seperated under the late Triassic period.

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The supercontinent Pangaea began to drift apart during the Jurassic Period. The Jurassic Period was the second segment of the Mesozoic Era. It occurred from 199.6 to 145.5 million years ago, following the Triassic Period and preceding the Cretaceous Period.

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In the seas, the fishlike ichthyosaurs were at their height, sharing the oceans with the plesiosaurs, withmarine crocodiles, and with modern-looking sharks and rays.

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Atmospheric oxygen levels have fluctuated throughout Earth's history, sometimes with catastrophic consequences. A sudden drop in oxygen, from roughly 30% of the atmosphere to about 10%, may have contributed to the mass extinctions at the end of the Permian period, 250 million years ago

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The Jurassic time period is part of the Mesozoic Era and it it stretches from 201 mya to 145 mya.

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We have chosen Jurassic!