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20.12.2015 18:48 - Largest prehistoric animals Vol.1 Vertebrates part3 Dinosaurs ch.1 Theropods-Tyrannosaurus rex,most fearsome scavenger in history of animals,sequel
Автор: valentint Категория: Забавление   
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Последна промяна: 05.12.2016 22:59

Tyrannosaurus rex,king of lizards tyrants
imageLike other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, Tyrannosaurus fore limbs were short but unusually powerful for their size and had two clawed digits. Although other theropods rivaled or exceeded Tyrannosaurus rex in size, it was the largest known tyrannosaurid and one of the largest known land predators. In fact, the most complete specimen measures up to 12.3 m (40 ft) in length, up to 4 metres (13 ft) tall at the hips,and up to 6.8 metric tons (7.5 short tons) in weight.By far the largest carnivore in its environment, Tyrannosaurus rex may have been an apex predator, preying upon hadrosaurs, ceratopsians, and possibly sauropods,although some experts have suggested the dinosaur was primarily a scavenger. The debate about whether Tyrannosaurus was an apex predator or scavenger was among the longest ongoing feud in paleontology; however, most scientists now agree that Tyrannosaurus rex was an opportunistic carnivore, acting as both a predator and a scavenger.It is estimated to be capable of exerting one of the largest bite forces among all terrestrial animals.
onymized with Tyrannosaurus.
More than 50 specimens of Tyrannosaurus rex have been identified, some of which are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including its life history and biomechanics. The feeding habits, physiology and potential speed of Tyrannosaurus rex are a few subjects of debate. Its taxonomy is also controversial, as some scientists consider Tarbosaurus bataar from Asia to be a second species of the Tyrannosaurus and others maintaining the Tarbosaurus is a separate genus of dinonera of North American tyrannosaurids have also been synsaur. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus.
Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, located at the Field Museum of National History and known colloquially as FMNH PR2081 and nicknamed "Sue", measured 12.3 metres (40 ft) long, and was 4 metres (13 ft) tall at the hips.Mass estimates have varied widely over the years, from more than 7.2 metric tons (7.9 short tons) to less than 4.5 metric tons (5.0 short tons), with most modern estimates ranging between 5.4 metric tons (6.0 short tons) and 6.8 metric tons (7.5 short tons).One study in 2011 found that the maximum weight of Sue, the largest Tyrannosaurus, was between 9.5 and 18.5 metric tons (9.3–18.2 long tons; 10.5–20.4 short tons), though the authors stated that their upper and lower estimates were based on models with wide error bars and that they "consider [them] to be too skinny, too fat, or too disproportionate".Packard et al. (2009) tested dinosaur mass estimation procedures on elephants and concluded that those of dinosaurs are flawed and produce over-estimations; thus, the weight of Tyrannosaurus could have been much less than previously thought.Other estimations have concluded that the largest known Tyrannosaurus specimens had masses approachingor exceeding 9 tonnes.
The neck of Tyrannosaurus rex formed a natural S-shaped curve like that of other theropods, but was short and muscular to support the massive head. The forelimbs had only two clawed fingers,along with an additional small metacarpal representing the remnant of a third digit.In contrast the hind limbs were among the longest in proportion to body size of any theropod. The tail was heavy and long, sometimes containing over forty vertebrae, in order to balance the massive head and torso. To compensate for the immense bulk of the animal, many bones throughout the skeleton were hollow, reducing its weight without significant loss of strength.
The largest known Tyrannosaurus rex skulls measure up to 1.5 metres (5 ft) in length.Large fenestrae (openings) in the skull reduced weight and provided areas for muscle attachment, as in all carnivorous theropods. But in other respects Tyrannosaurus"s skull was significantly different from those of large non-tyrannosauroid theropods. It was extremely wide at the rear but had a narrow snout, allowing unusually good binocular vision.The skull bones were massive and the nasals and some other bones were fused, preventing movement between them; but many were pneumatized (contained a "honeycomb" of tiny air spaces) which may have made the bones more flexible as well as lighter. These and other skull-strengthening features are part of the tyrannosaurid trend towards an increasingly powerful bite, which easily surpassed that of all non-tyrannosaurids. The tip of the upper jaw was U-shaped (most non-tyrannosauroid carnivores had V-shaped upper jaws), which increased the amount of tissue and bone a tyrannosaur could rip out with one bite, although it also increased the stresses on the front teeth.
The teeth of Tyrannosaurus rex displayed marked heterodonty (differences in shape).The premaxillary teeth at the front of the upper jaw were closely packed, D-shaped in cross-section, had reinforcing ridges on the rear surface, were incisiform (their tips were chisel-like blades) and curved backwards. The D-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when Tyrannosaurus bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers; more widely spaced and also had reinforcing ridges.Those in the upper jaw were larger than those in all but the rear of the lower jaw. The largest found so far is estimated to have been 30 centimetres (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found.
While there is no direct evidence for Tyrannosaurus rex having had feathers, many scientists now consider it likely that T. rex had feathers on at least parts of its body, due to their presence in related species of similar size. Dr. Mark Norell of the American Museum of Natural History summarized the balance of evidence by stating that: "we have as much evidence that T. rex was feathered, at least during some stage of its life, as we do that australopithecines like Lucy had hair."
While skin impressions from a Tyrannosaurus rex specimen nicknamed "Wyrex" (BHI 6230) discovered in Montana in 2002,as well as some other giant tyrannosauroid specimens, show at least small patches of mosaic scales, others, such as Yutyrannus huali (which was up to 9 metres (30 ft) long and weighed about 1,400 kilograms (3,100 lb)), preserve feathers on various sections of the body, strongly suggesting that its whole body was covered in feathers.It is possible that the extent and nature of feather covering in tyrannosauroids may have changed over time in response to body size, a warmer climate, or other factors.
Over half of the known Tyrannosaurus rex specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. One study suggests that the rarity of juvenile Tyrannosaurus rex fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and so were not often fossilized. However, this rarity may also be due to the incompleteness of the fossil record or to the bias of fossil collectors towards larger, more spectacular specimens.In a 2013 lecture, Thomas Holtz Jr. would suggest that dinosaurs "lived fast and died young" because they reproduced quickly whereas mammals have long life spans because they take longer to reproduce.Gregory S. Paul also writes that Tyrannosaurus reproduced quickly and died young, but attributes their short life spans to the dangerous lives they lived.
When Tyrannosaurus rex was first discovered, the humerus was the only element of the forelimb known.For the initial mounted skeleton as seen by the public in 1915, Osborn substituted longer, three-fingered forelimbs like those of Allosaurus. However, a year earlier, Lawrence Lambe described the short, two-fingered forelimbs of the closely related Gorgosaurus. This strongly suggested that Tyrannosaurus rex had similar forelimbs, but this hypothesis was not confirmed until the first complete Tyrannosaurus rex forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex").The remains of "Sue" also include complete forelimbs.Tyrannosaurus rex arms are very small relative to overall body size, measuring only 1 metre (3.3 ft) long, and some scholars have labelled them as vestigial.
Another possibility is that the forelimbs held struggling prey while it was killed by the tyrannosaur"s enormous jaws. This hypothesis may be supported by biomechanical analysis. Tyrannosaurus rex forelimb bones exhibit extremely thick cortical bone, which have been interpreted as evidence that they were developed to withstand heavy loads. The biceps brachii muscle of a full-grown Tyrannosaurus rex was capable of lifting 199 kilograms (439 lb) by itself; other muscles such as the brachialis would work along with the biceps to make elbow flexion even more powerful. The M. biceps muscle of T. rex was 3.5 times as powerful as the human equivalent. A Tyrannosaurus rex forearm had a limited range of motion, with the shoulder and elbow joints allowing only 40 and 45 degrees of motion, respectively. In contrast, the same two joints in Deinonychus allow up to 88 and 130 degrees of motion, respectively, while a human arm can rotate 360 degrees at the shoulder and move through 165 degrees at the elbow. The heavy build of the arm bones, strength of the muscles, and limited range of motion may indicate a system evolved to hold fast despite the stresses of a struggling prey animal. In the first detailed scientific description of Tyrannosaurus forelimbs, paleontologists Kenneth Carpenter and Matt Smith dismisse notions that the forelimbs were useless or that Tyrannosaurus rex was an obligate scavenger.
As of 2014, it is not clear if Tyrannosaurus was endothermic (warm-blooded). Tyrannosaurus, like most dinosaurs, was long thought to have an ectothermic ("cold-blooded") reptilian metabolism. The idea of dinosaur ectothermy was challenged by scientists like Robert T. Bakker and John Ostrom in the early years of the "Dinosaur Renaissance", beginning in the late 1960s.Tyrannosaurus rex itself was claimed to have been endothermic ("warm-blooded"), implying a very active lifestyle. Since then, several paleontologists have sought to determine the ability of Tyrannosaurus to regulate its body temperature. Histological evidence of high growth rates in young Tyrannosaurus rex, comparable to those of mammals and birds, may support the hypothesis of a high metabolism. Growth curves indicate that, as in mammals and birds, Tyrannosaurus rex growth was limited mostly to immature animals, rather than the indeterminate growth seen in most other vertebrates.
A study conducted by Lawrence Witmer and Ryan Ridgely of Ohio University added detail to the known sensory abilities of Tyrannosaurus, finding that they shared the heightened sensory abilities of other coelurosaurs, highlighting relatively rapid and coordinated eye and head movements, as well as an enhanced ability to sense low frequency sounds that would allow tyrannosaurs to track prey movements from long distances and an enhanced sense of smell. A study published by Kent Stevens of the University of Oregon concluded that Tyrannosaurus had keen vision. By applying modified perimetry to facial reconstructions of several dinosaurs including Tyrannosaurus, the study found that Tyrannosaurs had a binocular range of 55 degrees, surpassing that of modern hawks, and had 13 times the visual acuity of a human, thereby surpassing the visual acuity of an eagle which is only 3.6 times that of a person. This would have allowed Tyrannosaurs to discern objects as far as 6 km away, which is greater than the 1.6 km that a human can see.Thomas Holtz Jr. would note that high depth perception of Tyrannosaurus may have been due to the prey it had to hunt; noting that it had to hunt horned dinosaurs such as Triceratops, armored dinosaurs such as Ankylosaurus and the duck billed dinosaurs may have had complex social behaviors. He would suggest that this made precision more crucial for Tyrannosaurus enabling it to, "get in, get that blow in and take it down." In contrast, Acrocanthosaurus had limited depth perception because they hunted large sauropods, which were relatively rare during the time of Tyrannosaurus.
Tyrannosaurus is notable for having very large olfactory bulbs and olfactory nerves relative to their brain size, the organs responsible for a heightened sense of smell. This suggests that the sense of smell was highly developed, and implies that tyrannosaurs could detect carcasses by scent alone across great distances. The sense of smell in tyrannosaurs may have been comparable to modern vultures, which use scent to track carcasses for scavenging. Research on the olfactory bulbs has shown that Tyrannosaurus rex had the most highly developed sense of smell of 21 sampled non-avian dinosaurs species.
Somewhat unusually among theropods, T. rex had very long cochlea of the ear. The length of the cochlea is often related to hearing acuity, or at least the importance of hearing in behavior, implying that hearing was a particularly important sense to tyrannosaurs. Specifically, data suggests that Tyrannosaurus rex heard best in the low-frequency range, and that low-frequency sounds were an important part of tyrannosaur behavior.
A 2012 study by scientists Karl Bates and Peter Falkingham suggested that the bite force of Tyrannosaurus could have been the strongest of any terrestrial animal that has ever lived. The calculations suggested that adult T. rex could have generated from 35,000 to 57,000 newtons of force in the back teeth, or the equivalent of three times the force estimated for a great white shark, 15 times the force of an African lion, 3 1/2 times the force of an Australian saltwater crocodile, 77 times the force of an adult human and around 7 times the estimated force for Allosaurus.However, even higher estimates were made by professor Mason B. Meers of the University of Tampa in 2003. In his study, Meers estimated a possible bite force of around 183,000 to 235,000 newtons or 18.3 to 23.5 metric tons; a bite force equivalent to that of the largest Megalodon shark specimens.
The debate about whether Tyrannosaurus was a predator or a pure scavenger is as old as the debate about its locomotion. Lambe (1917) described a good skeleton of Tyrannosaurus close relative Gorgosaurus and concluded that it and therefore also Tyrannosaurus was a pure scavenger, because the Gorgosaurus teeth showed hardly any wear. This argument is no longer taken seriously, because theropods replaced their teeth quite rapidly. Ever since the first discovery of Tyrannosaurus most scientists have speculated that it was a predator; like modern large predators it would readily scavenge or steal another predator"s kill if it had the opportunity.
Paleontologist Jack Horner has been a major advocate of the idea that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all, though Horner himself has claimed that he never published this idea in the peer reviewed scientific literature and used it mainly as a tool to teach a popular audience, particularly children, the dangers of making assumptions in science (such as assuming T. rex was a hunter) without using evidence.Nevertheless, Horner presented several arguments in the popular literature to support the pure scavenger hypothesis:
Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey.
Tyrannosaurs had large olfactory bulbs and olfactory nerves (relative to their brain size). These suggest a highly developed sense of smell which could sniff out carcasses over great distances, as modern vultures do. Research on the olfactory bulbs of dinosaurs has shown that Tyrannosaurus had the most highly developed sense of smell of 21 sampled dinosaurs.Opponents of the pure scavenger hypothesis have used the example of vultures in the opposite way, arguing that the scavenger hypothesis is implausible because the only modern pure scavengers are large gliding birds, which use their keen senses and energy-efficient gliding to cover vast areas economically.However, researchers from Glasgow concluded that an ecosystem as productive as the current Serengeti would provide sufficient carrion for a large theropod scavenger, although the theropod might have had to be cold-blooded in order to get more calories from carrion than it spent on foraging (see Metabolism of dinosaurs). They also suggested that modern ecosystems like Serengeti have no large terrestrial scavengers because gliding birds now do the job much more efficiently, while large theropods did not face competition for the scavenger ecological niche from gliding birds.
Tyrannosaur teeth could crush bone, and therefore could extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in coprolites (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur"s teeth were not well adapted to systematically chewing bone like hyenas do to extract marrow.
Since at least some of Tyrannosaurus‍"s potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger.On the other hand, recent analyses suggest that Tyrannosaurus, while slower than large modern terrestrial predators, may well have been fast enough to prey on large hadrosaurs and ceratopsians.
Other evidence suggests hunting behavior in Tyrannosaurus. The eye-sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them binocular vision slightly better than that of modern hawks. Horner also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is not obvious why natural selection would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception that stereoscopic vision provides.In modern animals, binocular vision is found mainly in predators.
A skeleton of the hadrosaurid Edmontosaurus annectens has been described from Montana with healed tyrannosaur-inflicted damage on its tail vertebrae. The fact that the damage seems to have healed suggests that the Edmontosaurus survived a tyrannosaur"s attack on a living target, i.e. the tyrannosaur had attempted active predation.There is also evidence for an aggressive interaction between a Triceratops and a Tyrannosaurus in the form of partially healed tyrannosaur tooth marks on a Triceratops brow horn and squamosal (a bone of the neck frill); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor.Since the Triceratops wounds healed, it is most likely that the Triceratops survived the encounter and managed to overcome the Tyrannosaurus. Paleontologist Peter Dodson estimates that in a battle against a bull Triceratops, the Triceratops had the upper hand and would successfully defend itself by inflicting fatal wounds to the Tyrannosaurus using its sharp horns.
When examining Sue, paleontologist Pete Larson found a broken and healed fibula and tail vertebrae, scarred facial bones and a tooth from another Tyrannosaurus embedded in a neck vertebra. If correct, these might be strong evidence for aggressive behavior between tyrannosaurs but whether it would have been competition for food and mates or active cannibalism is unclear.However, further recent investigation of these purported wounds has shown that most are infections rather than injuries (or simply damage to the fossil after death) and the few injuries are too general to be indicative of intraspecific conflict.Some researchers argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey were the larger marginocephalians and ornithopods. The other tyrannosaurids share so many characteristics that only small dromaeosaurs and troodontids remain as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to steal kills from smaller predators,although they may have had a hard time finding enough meat to scavenge, being outnumbered by smaller theropods. Most paleontologists accept that Tyrannosaurus was both an active predator and a scavenger like most large carnivores.
On July 23, 2014, evidence, for the first time, in the form of fossilized trackways in Canada, shows that tyrannosaurs may have hunted in groups.


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