The Triassic, Jurassic, and Cretaceous Periods Andrew Bret Wallis/ The Image Bank/ Getty Images Updated April 25, 2016. It may come as a shock to the average dinosaur buff, but the Triassic , Jurassic , and Cretaceous periods weren't originally designated as a way to keep track of long-extinct reptiles. Rather, these vast stretches of historical time were marked out by geologists to distinguish among various types of geologic strata (chalk, limestone, etc.) laid down tens of millions of years ago. Of course, since dinosaur fossils are usually found embedded in rock, paleontologists associate dinosaurs with the geologic period in which they lived--for example, "the sauropods of the late Jurassic." To put these geologic periods in the proper context, you should bear in mind that the Triassic, Jurassic and Cretaceous don't cover all of prehistory, not by a long shot. First came the Precambrian period , which stretched from the earth’s formation to about 542 million years ago.

The development of multicellular life ushered in the Paleozoic Era (542-250 million years ago), which embraced shorter geologic periods including (in order) the Cambrian , Ordovician , Silurian , Devonian , Carboniferous and Permian periods. continue reading below our video What are the Seven Wonders of the World It's only after all that that we reach the Mesozoic Era (250-65 million years ago), which includes the Triassic, Jurassic and Cretaceous periods. Next Page: The Triassic Period Prev Jurassic Period Article, Dinosaurs Information, Prehistoric Facts -- National Geographic This requires the latest version of Flash Player. Click here to download. 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. 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. Huge Dinosaurs 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. Jurassic Period Facts: Rise of the Dinosaurs | Exploring Lifes Mysteries Home > History > Dinosaurs > Jurassic Period Facts: Rise of the Dinosaurs Jurassic Period Facts: Rise of the Dinosaurs 9 E-mail Total: 19 How do we keep this site running? This post may contain affiliate links — the cost is the same to you, but we get a referral fee. Compensation does not affect rankings. Thanks! The Mesozoic era saw some incredibly amazing life forms that continue to puzzle paleontologists today. The Mesozoic era was divided in to three individual periods: the Triassic period, the Jurassic period and the Cretaceous period. Smack in the middle of the Mesozoic area, the Jurassic period itself was also divided in to three sections, the early, middle and late Jurassic periods.

The Jurassic period brought some amazing changes that bred some amazing prehistoric beasts in a time which fell between 146 and 200 million years ago. The Early Jurassic Period: the Liassic Epoch (176 to 200 Million Years Ago) The early Jurassic period, known also as the Liassic epoch came about 176 to 200 million years ago and was divided in to the Hettangian age, the Sinemurian age, the Pliensbachian age, and the Toarcian age. The beginning of the Jurassic period saw a rise of the dinosaurs after the Triassic period saw the extinction of many of the animals that thrived during that time. The early Jurassic period also brought a much warmer and wetter rainforest type of climate and as such it encouraged reptile expansion. The early Jurassic period saw a variety of other life as well including the Ammonites, marine reptiles and terrestrial animals. While the Triassic period saw the end of many creatures due to extinction it only saw the near extinction of Ammonoids. As the continents shifted during the early Jurassic period the initial continent break up was in motion and this wasn’t the only activity in the world’s oceans.

Ammonoid life began to evolve. It did so so quickly that Ammonites alone can be used as markers of fossil zones. Marine reptiles also saw the early Jurassic period as a prime time to evolve and Ichthyosaurs and Plesiosaurs continued to grow giving birth to new marine reptiles such as the Ichthyosaurus, Temnodontosaurus, Eurycleidus, Macroplata and Rhomaleosaurus. Terrestrial animals which made their appearance during the early Jurassic period include the Heterodontosaurids, Scelidosaurs, Tetanurae, Stegosaurs. Also showing their faces at this time were the smaller carnivores: Sphenosuchid and Protosuchid crocodilians, the new flying Pterosaur species and early mammals such as the Tritylodonts, Sphenodonts, and Lissamphibians.

The Middle Jurassic Period: The Dogger Epoch (176 to 161 Million Years Ago) The Separation of Pangea and the Rise of the Atlantic The middle Jurassic period, known as the Dogger epoch came about 176 to 161 million years ago and was divided in to the Aalenian age, the Bajocian age, the Bathonian age, and the Callovian age. The middle of the Jurassic period saw the beginning of the separation of Pangea in to Laurasia and Gondwana and the formation of the Atlantic Ocean. The middle Jurassic period saw both growth and reduction in life; however, it was certainly not as dramatic of a change as that during the beginning of the Jurassic period. The reason for such explosive growth at the beginning of the Jurassic period was the extinction of so many species during the Triassic period. Marine life during the Dogger epoch saw some thinning of marine life as Icthyosaurs diversity reduced; however this reduced diversity was met with increased numbers of existing species. Also during this period Pliosaurs grew to mammoth proportions, matching killer whales in mass.

It is during this time also that Plesiosaurs made their appearance even more known by multiplying in numbers and the Metriorhynchid crocodilians also stepped on to the scene. The Dogger epoch also saw the appearance of new terrestrial life including Cetiosaurs, Hypsilophodonts, Megalosaurs, and Brachiosaurs. As Cynodonts continued to grow during this time the Trithelodont Cynodonts saw the end of the line at the end of the epoch. In terms of mammals it is the middle of the Jurassic era that saw the evolution of what we consider “real” mammals. The end of the Jurassic Period: the Malm Epoch (161 to 146 Million Years Ago) The True Pinnacle of Dinosaur Life The end of the Jurassic period, known as the Malm epoch came about 161 to 146 million years ago and was divided in to the Oxfordian age, the Kimmeridgian age and the Tithonian age. The end of the Jurassic period is known to many as the true pinnacle of dinosaur life and it also saw the true break up of Pangea in to Laurasia and Gondwana.

The late Jurassic period saw some simply amazing creatures come to form as well as the growth of existing dinosaurs from the middle Jurassic period. One of the most abundant dinosaurs to roam the Earth during the end of the Jurassic period was the Sauropods. The Cetiosaurids of the middle Jurassic period come to be replaced by the Camarasaurs, Brachiosaurs and Diplodocids many of which were absolutely gargantuan in size. Along with the humongous beasts which began roaming the Earth during this time crocodiles, lizards, frogs, turtles, marine reptiles, flying reptiles and the first birds in existence graced the Earth as well. Jurassic Period Facts: Commonalities Among Dinosaurs While the Jurassic period is neatly divided by and for paleontologists in to three eras, which are in turn divided in to their own periods, Jurassic facts are not. Jurassic facts, species and artifacts are, in fact, often given the label of Jurassic without having a specific period of the Jurassic age pinned to them.

There are many facts that relate to broader concepts and events that occurred during the Jurassic period which do not specifically apply to one section or the other and instead can be applied to the entire stretch of time from the early to the late Jurassic era. Such facts and artifacts cover geography, tectonics, fauna and flora as well as common misconceptions or this time as well. The Breaking of Pangea into Laurasia and Gondwana As already mentioned above, during the Jurassic period the massive continent Pangea broke in to Laurasia and Gondwana; however, during the Jurassic period there were many other geographic changes afoot. The breaking of Pangea also brought the Gulf of Mexico in to existence and the North Atlantic Ocean came in to being. The Rise of North America, the Atlantic, the Gulf of Mexico, and the Rocky and Sierra Nevada Mountains The Atlantic Ocean of the beginning Jurassic period was a narrow ocean which bore very little resemblance to the Atlantic Ocean we know today. The lower Atlantic did not show itself until Gondwana broke apart during the Cretaceous period.

Due to the rainforest like climate of the Jurassic era there was no evidence of either ice caps or glaciers and due to the larger continents still being in existence there was not yet any evidence of land near the poles at this time either. The larger continents at this time were also rotating; however, different sections of the continent rotated at different rates and directions causing rift valleys which went on to cause what is now the North American continent to drift westwards. It is also during this time that the beginnings of the Rocky Mountains and Sierra Nevada mountains saw their beginnings. During the Jurassic period the sea levels also rose and caused flooding over large sections of the continents leaving behind shallow seas and rich sediment across the land. Plate Tectonics Help Dinosaurs Rule the World As plates continued to collide over this period not only were mountains created but so too were volcanoes which would, according to today’s paleontologists, assist dinosaurs in ruling the earth by eliminating the competition of other land roaming creatures. Fauna during the Jurassic period became more abundant for the most part following the extinction that occurred during the Triassic period with the exception of a few species which became less diverse but more numerous.

Despite depictions in Steven Spielberg’s film “Jurassic Park” dinosaur life during the Jurassic period was not filled with Tyrannosaurus Rex living alongside Velociraptors and Brachiosaurus. Despite the depictions of the Hollywood inspired dino park the truth of the matter is that many of the dinosaurs depicted in Spielberg’s Jurassic Park were not even in existence during the Jurassic period. Take for example the Tyrannosaurus Rex and the Velociraptor, neither of which were walking the Earth until the Cretaceous period. There were, however, many large as well as vicious dinosaurs which roamed the Earth during the Jurassic period and they fell in to three families, the Sauropods, the Theropods, and the Ornithopods. The Sauropods The Sauropods of the Jurassic period were the dinosaurs that were characterized by long necks and long tails. Sauropods are also known by paleontologists as the largest living things to ever walk the Earth, some reaching as large as 190 feet long! Some of the most recognized Sauropods of the Jurassic era include: Diplodocus, Apatosaurus, Brachiosaurus, and the Amygdalodon.

The Theropods of the Jurassic period were the dinosaurs that were bipedal and almost all of them were carnivorous. Some of the most recognized Theropods of the Jurassic era include: Ceratosaurus, Megalosaurus, Magnosaurus, and Archaeopteryx. The Ornithopods of the Jurassic period were the dinosaurs who had bird like hips (characterized by a backwards pointing pelvis), were herbivores, had a beak and switched from being quadrupedal to being bipedal. Some of the most recognized Ornithopods of the Jurassic era include the Iguanodon, Agilisaurus and the Phyllodon. Jurassic Period Plant Life: Age of Cycads Flora during the Jurassic period was abundant and conducive to thriving dinosaur populations. As the warmer seas rose to cover continents in shallow seas fertile and moist ground gave way to thick and tall plant life. Cycads were especially abundant during the Jurassic period which is why many paleontologists refer to this time as the “Age of Cycads”. Cycads are plants which grow from seeds and flourish into plants whose leaves resemble palms.

The moist environment of the Jurassic period also provided ideal conditions for thriving jungles which grew to cover large portions of land. Conifers also thrived during the Jurassic era growing large tall trees as well as taking over low latitude vegetation with the Mesozoic era Cheirolepidaceae. Other shrubs and ferns which took over forest life include the Cycads, Ginkgos and Dicksoniaceous tree ferns. Rich Plant Life Helps Dinosaurs Grow and Expand It is not only the land which was conducive to flora life though, as the oceans underwent change. So too did ocean life, and algae became more sparse. It is during the Jurassic period that Coralline algae made its first appearance. As a result of such luscious and thick plant life during the Jurassic era dinosaurs were able not only to rule the Earth but they were able to diversify to allow the coming of the Cretaceous period which brought with it many more fierce creatures. It is even thought by some that such rich a dense plant life and vegetation gave rise to the gigantic size of the dinosaurs which were to come during the last age of the dinosaurs – the Cretaceous period. When and How did the Jurassic Period End?

As the Jurassic period came to a close it ended in a similar way to which it began. The Jurassic period began with a huge mass extinction which eliminated some of the biggest dinosaurs of the Triassic period. While the end of the Jurassic period did not bring such a dramatic change it did, in fact, bring a closing of doors for some major dinosaur species. The extinction, or “dying out” that came to be at the end of the Jurassic period obviously fell short of the mass extinction at the end of the Cretaceous period in magnitude as well; however, it did create some rather huge changes for dinosaur life. Dinosaurs continued to remain dominant over the land during the following Cretaceous period, although the smaller dinosaurs that saw the end of the Jurassic period had no idea of the mammoth dinosaurs that were to be ushered in with their small extinction event. While it is unknown as to what caused the minor mass extinction that accompanied the end of the Jurassic period it is known that it brought the end to quite a few species of dinosaur. Among the dinosaurs that saw their end ushered in with the end of the Jurassic era were the majority of the giant Sauropods such as Mamenchisaurus, Diplodocus and Brachiosaurus.

The transition in to the Cretaceous period also saw the end of the majority of Stegosaurids including the Stegosaurus, Kentrosaurus and Tuojiangosaurus. Additionally many genera of ammonoids, marine reptiles and bivalves saw their end of days as the Jurassic period drew to a close. While unfortunate for these species that did not live through to the beginning of the Cretaceous period their extinction played a role in the evolution of the real kings of dinosaurs who trod the Earth during the age of gigantism – the Cretaceous period. Lean More Find out more about Jurassic period at the Smithsonian either in person at the National Museum of Natural History or online at their Department of Paleobiology . Jurassic Period Facts: Dinosaurs, Mammals, Plants Jurassic Period Facts April 15, 2013 07:46pm ET MORE 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. Brachiosaurus was about as high as a four-story building. Credit: Linda Buckin Shutterstock 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. Latest on Jurassic Period Facts: Dinosaurs, Mammals, Plants Triassic Period, Mesozoic Era Information, Dinosaur Facts -- National Geographic This requires the latest version of Flash Player. Click here to download.

The start of the Triassic period (and the Mesozoic era) was a desolate time in Earth's history. Something—a bout of violent volcanic eruptions, climate change, or perhaps a fatal run-in with a comet or asteroid—had triggered the extinction of more than 90 percent of Earth's species. But it was also a time of tremendous change and rejuvenation. Life that survived the so-called Great Dying repopulated the planet, diversified into freshly exposed ecological niches, and gave rise to new creatures, including rodent-size mammals and the first dinosaurs. By the start of the Triassic, all the Earth's landmasses had coalesced to form Pangaea, a supercontinent shaped like a giant C that straddled the Equator and extended toward the Poles. Almost as soon as the supercontinent formed, it started to come undone. By the end of the period 199 million years ago, tectonic forces had slowly begun to split the supercontinent in two: Laurasia in the north and Gondwana in the south. The giant ocean called Panthalassa surrounded Pangaea.

Areas near the coast were pummeled by seasonal monsoons, but ocean-circulation patterns kept the isolated and vast interior warm and dry. Even the Poles were ice-free. The Tethys Ocean filled the C and was the zipper upon which Pangaea began to split apart. Earlier failed attempts at the split formed rift valleys in North America and Africa filled with red sediments that today contain the best preserved fossils of Triassic life. Triassic Animal Life The oceans teemed with the coiled-shelled ammonites, mollusks, and sea urchins that survived the Permian extinction and were quickly diversifying. The first corals appeared, though other reef-building organisms were already present. Giant reptiles such as the dolphin-shaped ichthyosaurs and the long-necked and paddle-finned plesiosaurs preyed on fish and ancient squid. The bottom rung of the food chain was filled with microscopic plants called phytoplankton; two of the major groups still in the oceans today first appeared. Frogs, salamanders, crocodiles, turtles, and snakes slunk and slithered on and off the Triassic coast, lakes, and rivers.

Pterosaurs, a group of flying reptiles, took to the air. On firm ground, moss, liverwort, and ferns carpeted forests of conifers, ginkgoes, and palm-like cycads. Spiders, scorpions, millipedes, and centipedes thrived. Grasshoppers appeared. But perhaps the biggest changes came with the evolution of dinosaurs and the first mammals in the late Triassic, starting around 230 million years ago. One of the earliest true mammals was the three-foot-long (one-meter-long) Eozostrodon. The shrewlike creature laid eggs but fed its young mother's milk. Among the first dinosaurs was the two-footed carnivore Coelophysis, which grew up to 9 feet (2.7 meters) tall, weighed up to a hundred pounds (45 kilograms), and probably fed on small reptiles and amphibians. It showed up about 225 million years ago. A few million years later came the 27.5-foot-long (8-meter-long) herbivore called Plateosaurus. The Triassic closed in the same way it began.

Something—perhaps a volcanic belch or an asteroid collision—caused another mass extinction. Dinosaurs, however, survived and went on to dominate the Jurassic. end-Triassic extinction | Britannica.com End-Triassic extinction evolution End-Triassic extinction, also called Triassic-Jurassic extinction, global extinction event occurring at the end of the Triassic Period (252 million to 201 million years ago) that resulted in the demise of some 76 percent of all marine and terrestrial species and about 20 percent of all taxonomic families. It is thought that the end-Triassic extinction was the key moment that allowed the dinosaurs to become the dominant land animals on Earth. The event ranks fourth in severity of the five major extinction episodes that span geologic time . The diversity of marine animal families since late Precambrian time. The data for the curve … Encyclopædia Britannica, Inc.

Although this event was less devastating than its counterpart at the end of the Permian Period , which occurred roughly 50 million years earlier and eliminated more than 95 percent of marine species and more than 70 percent of terrestrial ones (see Permian extinction ), it did result in drastic reductions of some living populations. The end-Triassic extinction particularly affected the ammonoids and conodonts , two groups that serve as important index fossils for assigning relative ages to various strata in the Triassic System of rocks . Indeed, the conodonts and many Triassic ceratitid ammonoids became extinct. Only the phylloceratid ammonoids were able to survive, and they gave rise to the explosive radiation of cephalopods later in the Jurassic Period . In addition, many families of brachiopods , gastropods , bivalves , and marine reptiles also became extinct. On land a great part of the vertebrate fauna disappeared, although the dinosaurs, pterosaurs , crocodiles , turtles , mammals , and fishes were little affected by the transition. In fact, many authorities maintain that the end-Triassic mass extinction on land opened ecological niches that were filled relatively quickly by dinosaurs.

Plant fossils and palynomorphs ( spores and pollen of plants) show no significant changes in diversity across the Triassic-Jurassic boundary. Similar Topics BBC Nature - Jurassic period videos, news and facts Time of the titans - dinosaurs of the Jurassic By Dr Jo Wright At the beginning of the Jurassic, dinosaurs started getting bigger. As vegetarians grew in size, so did the creatures that hunted them. Dr Jo Wright describes life in the time of the titans. Late Jurassic Earth The earliest dinosaurs were pretty small.Eoraptor was about one metre long. Its contemporary Herrerasaurus grew no more than four metres long and Coelophysis was about three metres long. And in all cases the length was mostly tail. However the plant-eating prosauropod, Plateosaurus, that appeared at the end of the Triassic period, was a harbinger of things to come. At up to nine metres long it was the first really big dinosaur. Prosauropods could walk either on all fours or just on their hind legs, leaving their hands free, perhaps to grasp branches and bring them within reach of their mouths.

They disappeared at the end of the Early Jurassic period and their role was taken by the sauropods which thrived during from the Middle Jurassic to the Early Cretaceous period. Sauropods had huge elephantine bodies coupled with very long necks and tails. They walked only on all fours. Some such as Diplodocus could probably have reared up on their hind legs using their tails as props. Diplodocus skeletons show a number of features that support this: They have high vertebral spines over the hip region, showing the creatures had strong muscles and ligaments there. They also have skid-like bones underneath their tails, which would have protected delicate nerves and blood vessels when their tales were resting on the ground. Keep on growing In the Early Jurassic the maximum size of both herbivores and carnivores increased. This trend continued throughout the Jurassic culminating in the staggeringly large sauropods such as Apatosaurus and Brachiosaurus. Carnivores had also increased in size, although not by as much and the 12 metre long Allosaurus was dwarfed by its sauropod prey. Allosaurus would have had to pick on the young or weak or may have hunted in packs.

Evidence based on growth rings and bone texture indicates that sauropods reached their adult size in 10-20 years. If, as was once suggested, sauropods took 70 years to reach maturity, it would be unlikely that many would survive to reproduce. The data suggesting that they grew quickly also fits that from the bones of theropods and ornithopods, who were thought to reach maturity fast. Impressive plates Stegosaurus was an early armoured dinosaur and its defences were formidable. Later armoured dinosaurs were veritable living tanks - some even had armoured eyelids! There are two main types of dinosaurs, named from the configuration of their pelvic bones: bird-hipped and lizard-hipped. Sauropods and theropods are lizard-hipped dinosaurs; Stegosaurus is a bird-hipped dinosaur, an early member of a group which became much more common and diverse in the Cretaceous period. A cruel sea - when reptiles ruled the waves The Mesozoic era truly was the age of giants. While huge dinosaurs dominated the land, large marine reptiles ruled the seas. Dr Jo Wright describes life in Jurassic seas.

Late Jurassic Earth The Ichthyosaurs (fish reptiles) appeared much earlier than the dinosaurs. They are first found in the Early Triassic, and they are already very specialised, with limbs modified into flippers. By the Jurassic, ichthyosaurs looked very like dolphins. They even had a dorsal fin and a big vertical tail fluke - we know this from some fossils in Germany which have the body outline preserved as a carbonised film. Ichthyosaurs propelled themselves through the water with strong side to side movements of their tails, steering with their flippers. The rise of plesiosaurs Plesiosaurs arose in the Late Triassic but became very numerous in the Middle and Late Jurassic. They used their flippers to move through the water. There were two kinds of plesiosaurs. The large short-necked pliosaurs were the top predators of Jurassic seas. Long-necked plesiosaurs probably fed on small fish and other small prey. We known they ate squid-like animals because parts of belemnites have been found in their fossilised stomachs. As well as large ichthyosaurs and giant pliosaurs, other reptilian denizens of the Middle-Late Jurassic seas were the marine crocodiles.

There were a couple of different types, one of which was so adapted to life in the seas that their limbs had turned into flippers and they even had a fluke on their tails to help them push themselves more efficiently through the water. Ammonites are very common fossils in Jurassic rocks. When they were alive, these molluscs looked as if a small squid had been stuffed into a spiral shell. They were very successful in the Jurassic although they were probably rather slow moving; we know from fossil stomach contents that they ate crinoids (sea lilies) - animals that are attached to the seabed. Still a mystery Mesozoic marine reptiles are already so specialised when they are first found in the fossil record that it is difficult to trace their ancestry. We have very little idea which groups of land reptiles ichthyosaurs and plesiosaurs descended from, but this only makes them all the more intriguing. Geological time When Dinosaurs Lived | Scholastic When Dinosaurs Lived Fun facts about the Triassic, Cretaceous, and Jurassic periods Grades 3–5, 6–8 Q: What was the difference between the Triassic, Cretaceous, and Jurassic periods?

A: We define these periods as measurements of time and communities of life. The Triassic was a time of a single world continent, when the first pterosaurs took flight and dinosaurs evolved along with many other animals. In the Jurassic, both plant-eating and meat-eating dinosaurs grew enormous. The world broke into two continents. In the Cretaceous, flowering plants and many insects evolved. Duck-billed dinosaurs and horned dinosaurs developed. T. rex ruled in these last dinosaur days. Q: How do you know which period certain dinosaurs lived? A: Usually you can tell the time when the dinosaur lived by the age of the rock it is in. You tell the rock's age by small fossils of plants and little animals that we already know the age of. If it is volcanic rock, you can tell its age by chemical testing. Sometimes we can tell the age of the rock and the fossils in it within 100,000 years of the actual time, even if it happened 300 million years ago. Q: Which time period had the most dinosaurs? A: Most dinosaurs we know come from the end of the Cretaceous period.

But dinosaurs probably lived in great numbers in all three periods of dinosaur time: Jurassic, Triassic, and Cretaceous. We haven't found as many dinosaurs from the other two periods because the rocks from that time aren't near the surface in places we have looked. We know more dinosaurs from the Cretaceous period than any other. That's just luck, since more rock from that time is now handy for excavating. We know about 175 kinds of dinosaurs from just the last 25 million years of dinosaur time. That's about half the total from all 165 million years they were around. Q: Can you describe the Cretaceous period? A: The Cretaceous was the last of the three periods of the Mesozoic Era, and dinosaurs lived in all three. The Cretaceous was a time when the seas were higher than ever before or after in Earth's history. The modern continents were taking shape and the first butterflies, bees, and flowers appeared. Duck-billed dinosaurs, horned dinosaurs, armored dinosaurs, giant meat-eaters like T. rex, and nasty little ones like the raptors all lived in the Cretaceous.

It started 144 million years ago and ended with the extinction of the dinosaurs and many other large animals, 65 million years ago. Q: What type of dinosaur was most abundant near the end of the Cretaceous period? A: The fossils most found at the end of the Cretaceous are duck-billed dinosaurs like Edmontosaurus and horned dinosaurs like triceratops. They traveled in huge herds in the North American West. At any time, predators are much more rare, which is one reason we don't have a lot of T. rex — only about 15 reasonable skeletons (more than 1/3 full) in 100 years. Q: Which Mesozoic period had the smallest dinosaur? A: The smallest dinosaurs were probably from the late Triassic and early Jurassic. That's where we find the smallest ornithischian dinosaurs so far. Dinosaurs got biggest in the late Jurassic and Cretaceous. Q: What is the most dangerous dinosaur period? A: The most dangerous dinosaur period of the three was probably the Cretaceous, since the biggest, meanest predators lived then, including T. rex which came right at the end of dinosaur time.

Q: How hot was it when the dinosaurs lived? A: The temperature varied, but generally it was hotter than today, with only a little snow in some polar places like Australia (in those days) once in a while. Q: Where did the velociraptor live and when? A: Velociraptor lived in Mongolia about 80 million years ago. Two years ago, it lived as a robot and computer animation for a short time in Hollywood during the making of Jurassic Park. Q: In what period did gigantosaurus live? A: It lived in the Late Cretaceous, about 90 million years ago. Q: Why weren't people alive when dinosaurs lived? A: People evolved from earlier mouse-sized mammals that were around all through dinosaur time but didn't get any bigger than a house cat. Only after the dinosaurs disappeared 65 million years ago did mammals get larger and more varied. Eventually, the primate mammals, the ape family, emerged and led to one very smart ape about one million years ago — us. Q: Did the woolly mammoth live when people were here? A: Yes, the woolly mammoth lived when the first Americans, Indians, were on this continent.

They also lived in Asia. The native people hunted the mammoths with spears and other tools. They hunted them so well that they may have been the reason these and other giant animals from 15,000 years ago or more went extinct. Dinosaurs went extinct long before people came along. ×

Question: What period came before the Jurassic?
Answer: The Triassic