DINOSAURS OF THE JURASSIC PERIOD I am writing this paper on the Jurassic Period. I will be talking about the different periods of dinosaurs. What dinosaur life was like during the Jurassic Period. I will also be going more in depth with several dinosaurs that lived during the early, middle, and late Jurassic Period. The history of the Jurassic Period in North America as well as Mexico also caught my interest. The three ages of Dinosaurs were in the Triassic, Jurassic, and Cretaceous periods. First I would like to explain all 3 periods before getting into the Jurassic period more specifically.
The start of the Triassic period followed the Permian Extinction, an event of unknown cause that wiped out over two-thirds of land-dwelling vertebrates and 95 percent of ocean-dwelling species. It was during the late Triassic period that the mammal-like reptiles evolved into the first mammals. During the Triassic period, all of the earth’s continents were joined together into a vast landmass called Pangaea. There were as yet no polar ice caps, and the climate was hot and dry, punctuated by violent monsoons. Except for insects, the skies of the early Triassic period were relatively quiet.
The Triassic period wasn’t nearly as lush and green as the later Jurassic and Cretaceous periods, but it did see an explosion of various land-dwelling plants, including cycads, ferns, and Gingko-like trees. Part of the reason there were no enormous dinosaurs during the Triassic (along the lines of Brachiosaurus) is that there simply wasn’t enough vegetation to nourish them! During the Jurassic period, relatives of the small, quadrupedal, plant-eating prosauropods of the Triassic period gradually evolved into gigantic sauropods like Brachiosaurus and Diplodocus.
This period also saw the rise of medium- to large-sized theropod dinosaurs like Allosaurus and Megalosaurus, which helps explain the evolution of the earliest ankylosaurs (armored herbivorous dinosaurs). The Jurassic period was also the heyday of the stegosaurs, typified by Stegosaurus. The climate was hot and humid, with steady rainfall, ideal conditions for the explosive spread of lush, green plants. By the end of the Jurassic period, the skies were filled with relatively advanced pterosaurs like Pterodactylus, Pteranodon and Dimorphodon.
Prehistoric birds had yet to fully evolve, leaving the skies firmly under the sway of these avian reptiles (with the exception of some prehistoric insects). During the early Cretaceous period, the inexorable breakup of the Pangaean supercontinent continued, with the first outlines of modern North and South America, Europe, Asia and Africa taking shape. Conditions were as hot and muggy as in the Jurassic, with the added twist of rising sea levels and the spread of endless swamps. It was during the Cretaceous period that dinosaurs really came into their own.
Thousands of genera roamed the slowly separating continents, including raptors and tyrannosaurs. The main innovation of the Cretaceous period was the evolution of flowering plants, which spread across the separating continents, along with thick forests and other kinds of dense, matted vegetation; this is also when grass first started to appear on the scene. At the end of the Cretaceous period, 65 million years ago, a meteor impact on the Yucatan Peninsula raised huge clouds of dust, blotting out the sun and causing most of this vegetation to die out.
The herbivorous dinosaurs that fed on the plants died, as did the carnivorous dinosaurs that fed on the herbivorous dinosaurs. There are four dinosaurs I would like to talk about during the Early Jurassic period and they are Ammosaurus, Crylophosaurus, Dilophosaurus, and Podokesaurus. Ammosaurus Dinosaur lived during the early Jurassic period, around 180 million years ago. It was a herbivore and could walk on both four or two feet, the latter undoubtably allowing it to reach higher branches. It had large claws on its hands to allow it to strip bark from trees and saplings.
Compared to the relax of its body, Ammosaurus had both a long tail & neck, suggesting that it would have walked on four legs for most of its life, only on foot on two to defend itself or reach food. To defend itself, it would stand on its hind legs, slashing at its assailant with its large thumb claws on its fore legs. Ammosaurus Dinosaur measured over< 4. 3 m (14 ft) long and stood about 1. 8 m (6 ft) tall, though it would only be knee high if it was on all fours. At its largest, it would grow to the size of a small car.
Cryolophosaurus was 6 to 8 meters (20 to 26 feet) long, which is significantly smaller than the largest Allosaurus, which reached up to 12 meters (40 feet) in length. A high, narrow skull was exposed, which measures 65 centimeters (25 inches) in length. The peculiar nasal crest runs just over the eyes, where it rises up, and perpendicular to the skull, and fans out. It is wrinkled, giving it a comb-like appearance. The crest is actually an extension of the skull bones which lie near the tear ducts (the lachrymals), fused on either side to horns which go up from the eye sockets (orbital horns).
While other theropods like the Monolophosaurus have crests, they usually run along the skull instead of across it. The crest is too fragile to be used in combat, so it was almost certainly used in mating displays. The Dilophosaurus was an aggressive carnivore and was one of the biggest for the region it was found (Tuba city, Arizona , USA ). It is determined that Dilophosaurus probably hunted and lived in herds because there were discoveries with up to three complete skeletons found together.
This dinosaur had many interesting features such as short hind legs, four toed feet, short forelimbs, three fingered hands, and an opposable thumb for each hand. The claws of the Dilophosaurus were very thick for the size of the prehistoric predator. They were probably its main offense along with its size. The strong hind legs showed that it could probably run like a horse. Out in the open its estimated top speed was 26(mph). As for its mouth, it had a loose weak jaw so this probably was not the animals’ main offensive weapon for hunting.
One of the most unique features of the Dilophosaurus was the two large crests upon its head. The rounded pair of semicircular bony crests was on its head faced vertically and the structure of them was fragile in certain areas. In these area’s they were reinforced with struts on strong bone. Podokesaurus can be considered an eastern variant of Coelophysis, a small, two-legged predator that lived in the western U. S. over the Triassic/Jurassic boundary (some experts even believe that Podokesaurus was really a species of Coelophysis).
This early theropod had the same long neck, grasping hands, and two-legged posture as its more famous cousin, and it was probably carnivorous (or at the very least an insectivore). Unfortunately, the only fossil of Podokesaurus (which was discovered way back in 1911 in the Connecticut Valley in Massachusetts) was destroyed in a museum fire a few years later; now, researchers have to content themselves with a plaster cast that currently resides at the American Museum of Natural History in New York. Now we are going to move on the Middle Jurassic and talk about a few dinosaurs that lived during that period.
Chialingosaurus was the first in a long series of Asian stegosaur discoveries. This early stegosaur was modestly sized (only about 13 feet long and 500 pounds), and probably subsisted not on tree leaves, but on ferns and cycads growing in the Jurassic soil. Thanks to its small build, it’s possible that Chialingosaurus was able to rear back on its hind legs to ward off predators or nip at low-lying branches. To date, though, Chialingosaurus is represented by limited fossil remains, so it may yet wind up being assigned to another genus of stegosaur. Chialingosaurus was about 13 Ft long and estimated at about 500 lbs.
It was smaller than most dinosaurs with a narrow skull and pointed rear spikes. Barapasaurus is inquisitive for the reason that it is the most primitive known sauropod, dating from the near the beginning of the Jurassic Period – more specifically the Toarcian age, about 189. 6 to 176. 5 million years ago. This is apparent in the unspecialized character of its form. Later sauropods like Brachiosaurusurbanized their own environmental alcove and feeding strategies. Conversely, Barapasaurus was a bit of an “all-purpose” dinosaur. Like all sauropods, Barapasaurus was an herbivore.
However, no cranium has yet been hauled and so its precise diet has not been dogged. A few isolated teeth are identified but not adequate to formulate judgments on the nature of its diet. Barapasaurus is also significant for the reason that, although its vestiges were found in India, it is extremely analogous to further samples spotted in East Africa. Cetiosaurus is one of those dinosaurs that was discovered ahead of its time: the first fossil specimen was unearthed in the early 19th century, before paleontologists had grasped the enormous sizes attained by the sauropods (other examples of which are Brachiosaurus and Apatosaurus).
At first, it was thought that this bizarre creature was a giant whale or crocodile, hence its name (which was bestowed by the famous paleontologist Richard Owen). The most unusual feature of Cetiosaurus was its backbone. Unlike some other sauropods, which had hollow vertebrae (an adaptation that helped to reduce their crushing weight), this huge herbivore had vertebrae of solid bone, which may account for the 25 tons or so it packed into its medium length. Paleontologists also speculate that Cetiosaurus roamed the Jurassic plains of western Europe and northern Africa in packs, rumbling along at speeds possibly approaching 10 miles per hour.
Lapparentosaurus was first thought to belong to the genus of the English sauropod Bothriospondylus. Closer examination, however, revealed that this was a more primitive species, featuring a short snout, shortened tail and front legs at least as long as the rear ones. Lapparentosaurus appears to have been closely related to Brachiosaurus. This dinosaur was named in 1986 by Bonaparte. It is likely that this sauropod is closely related to the better-known Brachiosaurus. Its vertebrae appear to be more primitive than other brachiosaurids. Lastly, I will be describing a few dinosaurs of the Late Jurassic period.
Allosaurus Dinosaur is the official state fossil of Utah, in the United States. Allosaurus is a classic big theropod: a big skull on a short neck, a long tail, and abridged forelimbs. Its most distinctive feature is a pair of blunt horns just above and in front of the eyes. Although short in assessment to the hindlimbs, the forelimbs are massive and bear large, eagle-like claws. The skull shows evidence of being self-possessed of separate modules, which could be moved in relation to one another, allowing big pieces of meat to be swallowed.
The skeleton of Allosaurus, like other theropods, shows birdlike features similar to a wishbone and neck vertebrae hollowed by air sacs. It is thought that Allosaurus might have necessary in packs, allowing it to bring down the huge sauropods of the time. Ceratosaurus is an unusual dinosaur. It was a carnivore (meat eater) that walked on two legs. It is instantly recognizable because it had a short horn on the end of its snout. Other noteworthy features of Ceratosaurus are its arms which each ended in four fingers (this is considered a primitive feature), and its powerful almost crocodile-like tail.
A fully grown adult Ceratosaurus was perhaps 15 to 20 feet (4. 5 to 6 meters) long, and perhaps weighed around a ton. The name “Ceratosaurus” means “horned lizard”, and refers of course to the horn on the end of the animal’s snout. This name was chosen by Ceratosaurus’ discoverer, Othniel C. Marsh. The first fossils of the animal were found in Cleveland Lloyd Dinosaur Quarry in Utah and Dry Mesa Quarry in Colorado, but a number of additional fossils have been found since that time.
Today, four different species of Ceratosaurus have so far been described, although some scientists believe that the fossils found to date may come from perhaps as many as six different species of the animal. Ceratosaurus lived during the late Jurassic period, between approximately 156 million and 145 million years ago. It was found in North America, Africa, and perhaps Portugal. Compsognathus dinosaur is known from two almost complete skeletons, one from Germany that is 90 cm long, and one more from France that is 125 cm; other skeletons point to a size range from 70-140 cm. Teeth from Portugal have also been assigned to the genus.
Although the French specimen was initially described as a separate species (Compsognathus corallestris), both it and the German specimen are now thought to be Compsognathus longipes. A fractional foot has also been referred to Compsognathus, but this has subsequently been disproved. Compsognathus may have had only two fingers, since no bones of a third finger have been established. However, the hands are disarticulated, so this is still unsure. It appears that Compsognathus preyed on small vertebrates, since leftovers of the lizard Bavariasaurus have been found in its thoracic cavity.
For many years, Compsognathus was the only well known small theropod, and was thus compared to Archaeopteryx as a dinosaurian ancestor or family member of birds. It is now known that many other kinds of dinosaurs were more closely related A basic, medium-sized Carnosaur that bears outward resemblence to Dilophosaurus, Monolophosaurus actually bears an interesting evolutionary convergence; A crest atop its head, like that of the crested Coelophysids. Monolophosaurus’ crest, however, differed in that it was hollow, like the Lambeosaurine crests.
The hollow canals in the crest led to the nasal passage, suggesting Monolophosaurus could sing through its crest, again just like the Lambeosaurines. Monolophosaurus was discovered by paleontologists Currie & Zhao in 1994, the head & neck were found. There was also a discovery of pelvic fossils at a later date in Thailand. It is sometimes considered that Monolophosaurus was related to the Allosaurids, though there is little evidence to support any connection to any family, other than the obvious theropod ones. Monolophosaurus lived in China during the Jurassic, where the skull was found to have pre-mortem water indications.
In eastern North America, Late Triassic–Early Jurassic extensional basins were filled with red beds and other continental sediments, and pillow lavas were extruded into lake basins. The basaltic Watchung Flows of the Newark Basin are Early Jurassic in age, based on potassium-argon dating techniques that show them to be 185 million to 194 million years old. More than 150 metres (500 feet) of Lower Jurassic lake beds were deposited in various basins on the east coast; some of these bedded sediments may reflect orbital cycles.
Middle Jurassic volcanoclastic rocks have been found beneath sediments on the continental shelf of New England. Upper Jurassic marine sediments include clastics interfingering with carbonates in the Atlantic and Gulf Coast basins. Middle Jurassic strata include evaporites, red beds, carbonates, and shelf-margin reefs. The Smackover Formation of the Gulf Coast sequences is a sedimentary unit typical of the Middle Jurassic. In the western interior of North America, the Middle Jurassic is characterized by a series of six marine incursions.
These epicontinental seaways are referred to collectively as the Carmel and Sundance seas; the Carmel Sea is older and not as deep as the Sundance. In these epicontinental seaways, marine sandstones, mudstones, limestones, and shales were deposited—some with marine fossils. Fully marine sequences interfinger with terrestrial sediments deposited during times of low sea levels and with marginal marine sediments that accumulated in environments bordering the seaways. In the Late Jurassic, sea levels dropped in North America, and terrestrial sedimentation occurred across much of the continent.
The Morrison Formation, a clastic deposit of lacustrine and fluvial mudstone, siltstone, sandstone, and conglomerate, is famous for fossil-rich beds that contain abundant plant and dinosaur remains. Uplift of the continental interior occurred between central Arizona and southern California from the Late Triassic until the Middle Jurassic. Jurassic strata of late Oxfordian to early Kimmeridgian age are reported from the Cerro Pozo Serna, northwest-central Sonora, Mexico. The presence of these marine strata greatly alters previous paleogeographic reconstructions of the Tethyan embayment in this area.
Approximately 60% of the Sonorian molluscan fauna has been previously reported from Jurassic horizons in the Gulf of Mexico and west Texas regions. The remainders of the mollusks, have previously been reported from either the western interior United States or Canada. The Pozo Serna faunas seem to be zoo-geographically transitional between communities present in the southern North American Tethyan realm and regions within the central North American Tethyan realm. Additionally, the Pozo Serna fauna greatly resembles contemporaneous communities reported from the Jurassic of Morocco.
Corals from the Sonorian Jurassic prove to be, in large part, well-known central European and Algerian reef-building species. Jurassic period lasted 213 to 144 million years ago. At the start of the Jurassic most of the continents were joined together until the Atlantic began to form and the Americas split off from Africa. Eastern North America was mostly elevated and subject to erosion, which reduced the Appalachian region to a peneplain. Before the end of the period, the Appalachian borderland began to founder as the Atlantic Ocean continued to widen.
The Pacific border of North America, from California to Alaska, was submerged for most of the period. In the Early Jurassic, large areas of Arizona, Colorado, and Utah were apparently desert, and the sand was later consolidated into the white and pinkish Glen Canyon and Navajo sandstones, which now enhance the scenic beauty of the district. During the Upper Jurassic, the Logan Sea entered this area from the north. In its various advances and retreats, this body of water covered large areas of Montana, Idaho, Wyoming, Colorado, and Utah, depositing sandstone, shale, limestone, and some gypsum.
The retreat of the Logan Sea, toward the end of the period, was followed, probably in the Upper Jurassic but possibly in the Lower Cretaceous Period, by the deposition of the Morrison continental series of clays and sandstones, noted for its richness in fossil dinosaurs. The close of the Jurassic in North America was marked by widespread folding along the western border of the continent, accompanied by the intrusion of lava as the eastern edge of the plate that carries the Pacific Ocean was thrust beneath the westward drifting plate that carries the North American continent.
In this disturbance the Sierra Nevada, Klamaths, Cascades, Coast Ranges, and coastal mountains of Canada and Alaska were formed. Studies of oxygen isotopes, the extent of land flora, and marine fossils indicate that climates during Jurassic times were mild-perhaps 15°F (8°C) warmer than those of today. No glaciers existed during this period. The plant life of the Jurassic was dominated by the cycads, but conifers, ginkgoes, horsetails, and ferns were also abundant. Of the marine invertebrates, the most important were the ammonites.
The dominant animals on land, in the sea, and in the air were the reptiles. Dinosaurs, more numerous and more extraordinary than those of the Triassic period, were the chief land animals; crocodiles, ichthyosaurs, and plesiosaurs ruled the sea, while the air was inhabited by the pterosaurs and relatives. Mammals, making their first appearance, were few and small but undoubtedly became well established during the Jurassic period. The Jurassic saw the appearance of the first bird, Archaeopteryx. There was a minor mass extinction toward the end of the Jurassic period.
During this extinction, most of the stegosaurid and enormous sauropod dinosaurs died out, as did many genera of ammonoids, marine reptiles, and bivalves. No one knows what caused this extinction. Near the end of the Jurassic period several species died out giving rise to the Cretaceous period. This transition was not as violent as the mass extinction at the beginning of the Jurassic period nor as devastation as what would come near the end of the Cretaceous. I started by describing the Three Ages of Dinosaurs.
I described the life of the Jurassic Period and talked about the climate and geography, marine life and a little about plant life. There were several dinosaurs of the Early Jurassic, Middle Jurassic, and the Late Jurassic that I thought were rather interesting and that is why I chose to write about them. I think we learned a lot about Ammosaurus, Crylophosaurus, Dilophosaurus, Podokesaurus, Chialingosaurus, Barapasaurus, Cetiosaurus, Lapparentsaurus, Allosaurus, Ceratosaurus, Compsognathus, and the Monolophosaurus. I discussed the history of the Jurassic in North America in great depth and also Mexico.
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