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Tyrannosaurus Rex
JW T-Rex
'Tyrannosaurus as it appeared in Jurassic World'



Name Translation:

Tyrant Lizard King


Late Cretaceous (68-65 mya)


42-49 feet long(13-15 meters)


15-21 feet tall (5-7 meters)


6.6-9 tonnes

Tyrannosaurus meaning "king tyrant lizard" (Greek tyrannos = tyrant + sauros = lizard + rex = king), also known and simply as T. rex, was a large carnivorous theropod dinosaur that lived from 68-66 million years ago. Tyrannosaurus is the most-known- and famous dinosaur that has ever lived. Its fossil remains are relatively rare, as of 2012 only 44 specimens had been found, including three complete skulls. Tyrannosaurus rex measures from 37 to 43 feet (11–13 meters) long stands 13 feet (4 m) tall at hips, and weighs between 7 and 9 tons (14,000-18,000 lb), meaning this dinosaur was even bigger than the average African Elephant, and by far the largest carnivore ever in North America.

What's more is it's speculated that dinosaurs grew their whole lives, so its possible we'll find even bigger specimens in the near future. It lived throughout what is now western North America, with a much wider range than most other tyrannosaurids, including the states of Wyoming, Montana, North and South Dakota, Colorado, Canada, and even Texas. It was among the last non-avian dinosaurs to exist prior to the Cretaceous–Tertiary   Extinction Event. While Tyrannosaurus and its relatives ruled the north, abelisaurs such as Carnotaurus ruled the south. In fact, the tyrannosaurids were so successful, that whenever a tyrannosaur moved into an area anywhere within the northern hemisphere, all other large theropods were soon wiped out due to being in direct competition with them. So people have speculated about whether there may be more than one type of tyrannosaur in T.rex's environment.
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Tyrannosaurus rex is one of the most most well-known dinosaurs, ranging from toys to television shows. Its name still brings fear even today, and it's also celebrated as the "King of the Dinosaurs". It has become the quintessential dinosaur/monster, and an icon in dinosaur culture. In 1892, Edward Cope described the first known Tyrannosaurus rex skeleton as Manospondylus gigas, but this is now considered a Nomen oblitum. Barnum Brown's 1902 discovery of "Dynamosaurus imperiosus," is also now called Tyrannosaurus rex, Tyrannosaurus' type species. He found two more specimens, in 1902 and 1905. Tarbosaurus was at one point considered to be a second Asian species of Tyrannosaurus, but, despite similarities between the two, Tarbosaurus is now usually referred to as it's own species, Tarbosaurus bataar

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Tyrannosaurus rex was not the undisputed biggest carnivorous dinosaur, however. Spinosaurus may have been the biggest carnivore ever discovered, with the largest estimates being 52 feet (16 m), long though its habits indicate a more aquatic than terrestrial lifestyle, similar to those of crocodilians, and it's only based on fragments for the time being, so its exact size isn't truly known, but Tyrannosaurus was by far the biggest carnivore ever in North America. Three carnosaurs called Mapusaurus, Giganotosaurus and Carcharodontosaurus also compete against T. rex for the title of largest carnivorous dinosaur, but recent study on body structure shows that due to excessive body mass, the tyrant lizard was likely heavier than either contenders.

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Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, FMNH PR2081 ("Sue"), measured 12.8 metres (42 ft) long, and was 4.0 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 and 6.8 metric tons (6.0 and 7.5 short tons). Although Tyrannosaurus rex was larger than the well known Jurassic theropod Allosaurus, it was slightly smaller than Cretaceous carnivores Spinosaurus and Giganotosaurus.

The neck of T. rex formed a natural S-shaped curve like that of other theropods, but was short and muscular to support the massive head. The forelimbs were long thought to bear only two digits, but there is an unpublished report of a third, vestigial digit in one specimen. 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 T. rex skulls measure up to 5 feet (1.5 m) 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’ 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 T. 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.


Tyrannosaurus is the type genus of the superfamily Tyrannosauroidea, the family Tyrannosauridae, and the subfamily Tyrannosaurinae; in other words it is the standard by which paleontologists decide whether to include other species in the same group. Other members of the tyrannosaurine subfamily include the North American Daspletosaurus and the Asian Tarbosaurus, both of which have occasionally been synonymized with Tyrannosaurus. Tyrannosaurids were once commonly thought to be descendants of earlier large theropods such as megalosaurs and carnosaurs, although more recently they were reclassified with the generally smaller coelurosaurs.


Profile view of a Tyrannosaurus skull (AMNH 5027).

In 1955, Soviet paleontologist Evgeny Maleev named a new species, Tyrannosaurus bataar, from Mongolia. By 1965, this species had been renamed Tarbosaurus bataar. Despite the renaming, many phylogenetic analyses have found Tarbosaurus bataar to be the sister taxon of Tyrannosaurus rex, and it has often been considered an Asian species of Tyrannosaurus. A recent redescription of the skull of Tarbosaurus bataar has shown that it was much narrower than that of Tyrannosaurus rex and that during a bite, the distribution of stress in the skull would have been very different, closer to that of Alioramus, another Asian tyrannosaur. A related cladistic analysis found that Alioramus, not Tyrannosaurus, was the sister taxon of Tarbosaurus, which, if true, would suggest that Tarbosaurus and Tyrannosaurus should remain separate.

Other tyrannosaurid fossils found in the same formations as T. rex were originally classified as separate taxa, including Aublysodon and Albertosaurus megagracilis, the latter being named Dinotyrannus megagracilis in 1995. However, these fossils are now universally considered to belong to juvenile T. rex. A small but nearly complete skull from Montana, 60 centimetres (2.0 ft) long, may be an exception. This skull was originally classified as a species of Gorgosaurus (G. lancensis) by Charles W. Gilmore in 1946, but was later referred to a new genus, Nanotyrannus. Opinions remain divided on the validity of N. lancensis. Many paleontologists consider the skull to belong to a juvenile T. rex. There are minor differences between the two species, including the higher number of teeth in N. lancensis, which lead some scientists to recommend keeping the two genera separate until further research or discoveries clarify the situation.


Trex skull

Skull of T. rex, type specimen at the Carnegie Museum of Natural History. This was heavily and inaccurately restored with plaster using Allosaurus as a model, and has since been disassembled.

The first fossil specimen which can be attributed to Tyrannosaurus rex consists of two partial vertebrae (one of which has been lost) found by Edward Drinker Cope in 1892 and described as Manospondylus gigas. Osborn recognized the similarity between M. gigas and T. rex as early as 1917 but, due to the fragmentary nature of the Manospondylus vertebrae, he could not synonymize them conclusively.

In June 2000, the Black Hills Institute located the type locality of M. gigas in South Dakota and unearthed more tyrannosaur bones there. These were judged to represent further remains of the same individual, and to be identical to those of T. rex. According to the rules of the International Code of Zoological Nomenclature (ICZN), the system that governs the scientific naming of animals, Manospondylus gigas should therefore have priority over Tyrannosaurus rex, because it was named first. However, the Fourth Edition of the ICZN, which took effect on 1 January 2000, states that "the prevailing usage must be maintained" when "the senior synonym or homonym has not been used as a valid name after 1899" and "the junior synonym or homonym has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years..." Tyrannosaurus rex may qualify as the valid name under these conditions and would most likely be considered a nomen protectum ("protected name") under the ICZN if it was ever challenged, which it has not yet been. Manospondylus gigas would then be deemed a nomen oblitum ("forgotten name").


Life history

The identification of several specimens as juvenile Tyrannosaurus rex has allowed scientists to document ontogenetic changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The smallest known individual (LACM 28471, the "Jordan theropod") is estimated to have weighed only 29.9 kg (66 lb), while the largest, such as FMNH PR2081 ("Sue") most likely weighed over 5400 kg (6 short tons). Histologic analysis of T. rex bones showed LACM 28471 had aged only 2 years when it died, while "Sue" was 28 years old, an age which may have been close to the maximum for the species.

Histology has also allowed the age of other specimens to be determined. Growth curves can be developed when the ages of different specimens are plotted on a graph along with their mass. A T. rex growth curve is S-shaped, with juveniles remaining under 1800 kg (2 short tons) until approximately 14 years of age, when body size began to increase dramatically. During this rapid growth phase, a young T. rex would gain an average of 600 kg (1,300 lb) a year for the next four years. At 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only 600 kg (1,300 lb) separated the 28-year-old "Sue" from a 22-year-old Canadian specimen (RTMP 81.12.1). Another recent histological study performed by different workers corroborates these results, finding that rapid growth began to slow at around 16 years of age. This sudden change in growth rate may indicate physical maturity, a hypothesis which is supported by the discovery of medullary tissue in the femur of a 16 to 20-year-old T. rex from Montana (MOR 1125, also known as "B-rex"). Medullary tissue is found only in female birds during ovulation, indicating that "B-rex" was of reproductive age. Further study indicates an age of 18 for this specimen. Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.

Over half of the known T. 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 T. 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.

Sexual dimorphism

As the number of specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or morphs, similar to some other theropod species. As one of these morphs was more solidly built, it was termed the 'robust' morph while the other was termed 'gracile.' Several morphological differences associated with the two morphs were used to analyze sexual dimorphism in Tyrannosaurus rex, with the 'robust' morph usually suggested to be female. For example, the pelvis of several 'robust' specimens seemed to be wider, perhaps to allow the passage of eggs. It was also thought that the 'robust' morphology correlated with a reduced chevron on the first tail vertebra, also ostensibly to allow eggs to pass out of the reproductive tract, as had been erroneously reported for crocodiles.

In recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between T. rex genders. A full-sized chevron was discovered on the first tail vertebra of "Sue," an extremely robust individual, indicating that this feature could not be used to differentiate the two morphs anyway. As T. rex specimens have been found from Saskatchewan to New Mexico, differences between individuals may be indicative of geographic variation rather than sexual dimorphism. The differences could also be age-related, with 'robust' individuals being older animals.

Only a single T. rex specimen has been conclusively shown to belong to a specific gender. Examination of "B-rex" demonstrated the preservation of soft tissue within several bones. Some of this tissue has been identified as medullary tissue, a specialized tissue grown only in modern birds as a source of calcium for the production of eggshell during ovulation. As only female birds lay eggs, medullary tissue is only found naturally in females, although males are capable of producing it when injected with female reproductive hormones like estrogen. This strongly suggests that "B-rex" was female, and that she died during ovulation.[1] Recent research has shown that medullary tissue is never found in crocodiles, which are thought to be the closest living relatives of dinosaurs, aside from birds. The shared presence of medullary tissue in birds and theropod dinosaurs is further evidence of the close evolutionary relationship between the two.


Like many bipedal dinosaurs, Tyrannosaurus rex was historically depicted as a 'living tripod', with the body at 45 degrees or less from the vertical and the tail dragging along the ground, similar to a kangaroo. This concept dates from Joseph Leidy's 1865 reconstruction of Hadrosaurus, the first to depict a dinosaur in a bipedal posture. Henry Fairfield Osborn, former president of the American Museum of Natural History (AMNH) in New York City, who believed the creature stood upright, further reinforced the notion after unveiling the first complete T. rex skeleton in 1915. It stood in this upright pose for nearly a century, until it was dismantled in 1992. By 1970, scientists realized this pose was incorrect and could not have been maintained by a living animal, as it would have resulted in the dislocation or weakening of several joints, including the hips and the articulation between the head and the spinal column. The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as Rudolph Zallinger's famous mural The Age Of Reptiles in Yale University's Peabody Museum of Natural History) until the 1990s, when films such as Jurassic Park introduced a more accurate posture to the general public. Modern representations in museums, art, and film show T. rex with its body approximately parallel to the ground and tail extended behind the body to balance the head.


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 T. rex had similar forelimbs, but this hypothesis was not confirmed until the first complete T. rex forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex"). The remains of "Sue" also include complete forelimbs. T. rex arms are very small relative to overall body size, measuring only 1 metre (3.3 ft) long. However, they are not vestigial but instead show large areas for muscle attachment, indicating considerable strength. This was recognized as early as 1906 by Osborn, who speculated that the forelimbs may have been used to grasp a mate during copulation. It has also been suggested that the forelimbs were used to assist the animal in rising from a prone position. Another possibility is that the forelimbs held struggling prey while it was dispatched by the tyrannosaur's enormous jaws. This hypothesis may be supported by biomechanical analysis. T. rex forelimb bones exhibit extremely thick cortical bone, indicating 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; this number would only increase with other muscles (like the brachialis) acting in concert with the biceps. A T. rex forearm also had a reduced 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, extreme strength of the muscles, and limited range of motion may indicate a system designed to hold fast despite the stresses of a struggling prey animal.

Soft tissue

In the March 2005 issue of Science, Mary Higby Schweitzer of North Carolina State University and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone, from a 68-million-year-old Tyrannosaurus. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue. Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the Hell Creek Formation. Flexible, bifurcating blood vessels and fibrous but elastic bone matrix tissue were recognized. In addition, microstructures resembling blood cells were found inside the matrix and vessels. The structures bear resemblance to ostrich blood cells and vessels. Whether an unknown process, distinct from normal fossilization, preserved the material, or the material is original, the researchers do not know, and they are careful not to make any claims about preservation. If it is found to be original material, any surviving proteins may be used as a means of indirectly guessing some of the DNA content of the dinosaurs involved, because each protein is typically created by a specific gene. The absence of previous finds may merely be the result of people assuming preserved tissue was impossible, therefore simply not looking. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures.[2] Research on some of the tissues involved has suggested that birds are closer relatives to tyrannosaurs than other modern animals.

In studies reported in the journal Science in April 2007, Asara and colleagues concluded that seven traces of collagen proteins detected in purified T. rex bone most closely match those reported in chickens, followed by frogs and newts. The discovery of proteins from a creature tens of millions of years old, along with similar traces the team found in a mastodon bone at least 160,000 years old, upends the conventional view of fossils and may shift paleontologists' focus from bone hunting to biochemistry. Until these finds, most scientists presumed that fossilization replaced all living tissue with inert minerals. Paleontologist Hans Larsson of McGill University in Montreal, who was not part of the studies, called the finds "a milestone", and suggested that dinosaurs could "enter the field of molecular biology and really slingshot paleontology into the modern world."

Subsequent studies in April 2008 confirmed the close connection of T. rex to modern birds. Postdoctoral biology researcher Chris Organ at Harvard University announced, "With more data, they would probably be able to place T. rex on the evolutionary tree between alligators and chickens and ostriches." Co-author John M. Asara added, "We also show that it groups better with birds than modern reptiles, such as alligators and green anole lizards.

The presumed soft tissue was called into question by Thomas Kaye of the University of Washington and his co-authors in 2008. They contend that what was really inside the tyrannosaur bone was slimy biofilm created by bacteria that coated the voids once occupied by blood vessels and cells. The researchers found that what previously had been identified as remnants of blood cells, because of the presence of iron, were actually framboids; microscopic mineral spheres bearing iron. They found similar spheres in a variety of other fossils from various periods, including an ammonite. In the ammonite they found the spheres in a place where the iron they contain could not have had any relationship to the presence of blood.

Skin and feathers

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In 2004, the scientific journal Nature published a report describing an early tyrannosauroid, Dilong paradoxus, from the famous Yixian Formation of China. As with many other theropods discovered in the Yixian, the fossil skeleton was preserved with a coat of filamentous structures which are commonly recognized as the precursors of feathers. It has also been proposed that Tyrannosaurus and other closely related tyrannosaurids had such protofeathers. However, skin impressions from large tyrannosaurid specimens show mosaic scales. While it is possible that protofeathers existed on parts of the body which have not been preserved, a lack of insulatory body covering is consistent with modern multi-ton mammals such as elephants, hippopotamus, and most species of rhinoceros. And in 2012, another feathered tyrannosaurid, Yutyrannus huali, was discovered.

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As an object increases in size, its ability to retain heat increases due to its decreasing surface area-to-volume ratio. Therefore, as large animals evolve in or disperse into warm climates, a coat of fur or feathers loses its selective advantage for thermal insulation and can instead become a disadvantage, as the insulation traps excess heat inside the body, possibly overheating the animal. Protofeathers may also have been secondarily lost during the evolution of large tyrannosaurids like Tyrannosaurus, especially in warm Cretaceous climates. If anything, the feathers would've been used to show off during courtship to attract mates in large tyrannosaurs. Even though the larger adult tyrannosaurs probably didn't have any feathers, the babies, which were much smaller and needed more warmth than the adults, probably hatched with a full coat of downy feathers and lost them as they grew.


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 T. 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, T. rex growth was limited mostly to immature animals, rather than the indeterminate growth seen in most other vertebrates.

Oxygen isotope ratios in fossilized bone are sometimes used to determine the temperature at which the bone was deposited, as the ratio between certain isotopes correlates with temperature. In one specimen, the isotope ratios in bones from different parts of the body indicated a temperature difference of no more than 4 to 5°C (7 to 9°F) between the vertebrae of the torso and the tibia of the lower leg. This small temperature range between the body core and the extremities was claimed by paleontologist Reese Barrick and geochemist William Showers to indicate that T. rex maintained a constant internal body temperature (homeothermy) and that it enjoyed a metabolism somewhere between ectothermic reptiles and endothermic mammals. Other scientists have pointed out that the ratio of oxygen isotopes in the fossils today does not necessarily represent the same ratio in the distant past, and may have been altered during or after fossilization (diagenesis). Barrick and Showers have defended their conclusions in subsequent papers, finding similar results in another theropod dinosaur from a different continent and tens of millions of years earlier in time (Giganotosaurus).Ornithischian dinosaurs also showed evidence of homeothermy, while varanid lizards from the same formation did not. Even if Tyrannosaurus rex does exhibit evidence of homeothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by gigantothermy, as in some living sea turtles.

Killer Instinct

There has been ongoing debate as to how Tyrannosaurus found its food. Most people believe it was a predator, hunting down and killing its food in the same way modern lions do. However, others believe it was a scavenger, as evidenced by its large olfactory bulbs (which indicate a phenomenal sense of smell). The best
possible conclusion is that T. rex was both a part time hunter and scavenger, since no carnivore relies on just one of those things alone. Evidence has shown that T. rex was also cannibalistic (It may shock us, but Lions do this quite often) when the situation demanded it, or after killing its own kind for mating or territory. There's also evidence that Tyrannosaurus rex hunted in groups, from when Phil Currie found a large number of Tyrannosaurus' close, more primitive relative Albertosaurus in Canada that were all of different ages, and since Albertosaurus, which was more primitive and not as smart as its more famous cousin, hunted in groups, then why shouldn't T. rex have done the same?
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The concept that makes Tyrannosaurus rex so deadly is that it had a huge 5 foot (1.5 metre) long skull that weighed well over 500 lbs (225 kg) in weight and great jaws that could dislocate like a snake to swallow large pieces of meat. It also had banana-sized teeth (12 in. or 30 cm), some of the largest in the animal kingdom, and could bite 500-600 lbs. (227–273 kg.) of meat off at a time and swallow it whole, sometimes breaking the teeth off when biting but growing them back repeatedly. Unlike most predators, T. rex would also eat basically the whole carcass, bones and all. We know because we've found Tyrannosaurus coprolites (fossilized dung) with ceratopsian and hadrosaur bones in it. The teeth made Tyrannosaurus different from most predators, because these teeth were blunter, stronger, and more suited to crush bone and penetrate armor instead of slice through flesh. Another discovery seems to show that T. rex also had a very infectious bite from the teeth, since the serrations in the them were much larger than other theropoods, and probably held pieces of rotten meat in them, which allowed harmful bacteria to grow and cause disease when the Rex bit down on prey items, so even if the T. rex didn't get the kill on the first bite, the prey would eventually die of infection and the T. rex would just track it down using its keen sense of smell and eat it after it'd died or became too weak to fight. It


also seems as though T. rexes in the North fought against Triceratops, Ankylosaurus, Edmontosaurus, and Pachycephalosaurus, while ones in the South fought against all of those plus a large sauropod called Alamosaurus.

The average bite force of Tyrannosaurus rex astounded scientists when they used calculations from crocodile bite forces to find out that Tyrannosaurus rex had a bite force of 60,000 newtons (6.8 tons) of pressure and perhaps even more. 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 183000 to 235000 newtons or 18.3 to 23.5 metric tons; a bite force equivalent to that of the largest Megalodon shark specimens. Other studies say the neck could lift 5 tons. This tremendous amount of force is enough to easily crush bone and bite through a steel oil drum, and also is by far the most powerful bite force of any terrestrial animal that ever lived, surpassing any modern-day animal, such as sharks, crocodiles, or hippos. Tyrannosaurs could probably use hunting tactics which required lunging at prey from short distances, and then crushing them with its jaws. It also could break bones with it's tail, teeth, and could also do so by ramming into prey with its rock-hard head. T. rex was also the most muscularly built theropod ever, even its tiny arms were strong, being able to lift 500 lbs. (227 kg.) with each arm, crushing any Olympic record for weight-lifting. The exact use for its arms are unknown, but most scientists agree it was to grab onto struggling prey with those 2-inch (5-cm.) long, hook-like claws while its huge jaws finished it off with a bite to the neck. They also could've been used to grab on at first while mating or to help lift itself up off the ground. Most scientists agree that T. rex's arms got so small throughout evolution from its jaws becoming so big and powerful, so the arms were less needed, and if T. rex hadn't gone extinct, the arms might've completely disappeared all together.

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Although it was the top predator, Tyrannosaurus rex had a very tough life, most not even living past their early 30's (even Sue died at 29), but T. rex has proven to also be a very resilient dinosaur. Nearly every adult Tyrannosaurus specimen found has wounds that it have been healed, but would've killed nearly any other animal.For instance, in one specimen named Sue, it had suffered and survived injuries such as broken ribs, infections in the vertebrae and legs, and also had arthritis. Other specimens have also been healed from Triceratops horns, Ankylosaurus clubs, and even bitemarks from other tyrannosaurs. In fact one specimen nicknamed Stan even had a piece of the back of his skull and brain case bitten out of and he still lived for several more years. Aside from fighting some of the toughest herbivores that nature's ever produced, like Triceratops and Ankylosaurus, they also fought amongst themselves frequently. Nearly every complete or mostly complete skull found has bite marks from the only large theropod around, another T. rex. They most likely fought over mates, territory, or food. Tyrannosaurus and its cousins were so successful that whenever a tyrannosaur moved into a territory, it drove out any other large predator, and were soon the only large predators in the area.
T. rex's speed has been a topic of discussion for a while. The scientists that believe T. rex was a scavenger say that it was a slow-moving, lumbering animal that could barely run 15 mph. However, some speculate, that since T. rex had some of the longest and most muscular legs of any bipedal dinosaur, it was a fast runner. In fact its legs and pelvis alone made up half of the tyrant lizard's body weight, and the tail alone weighed a full ton, designed to hold extra muscle mass and counter-balance its enormous head. Another study on the famous Tyrannosaurus specimen nicknamed Sue also shows how deep indentations on the leg bones where muscle once was, suggesting high concentration of the tissue. Also, unlike most other large theropods, T. rex had a longer shin bone than a femur bone, giving it an ostirich-like build and shows that T. rex possibly was fairly fast. Scientists that believe T. rex was a predator say that it could run 25-28 mph (40–45 km/h), faster than Olympic sprinters! Ao far it was confirmed that T.rex was a slow reptile, running up to 11 mph (18 kph). Even though T. rex wasn't that fast, it was still capable of taking down large prey. It also seems as though if T. rex was a predator, than it held its prey down with one of its feet, using the other one and its long tail for balance, and then taking a bite out if its prey's neck, severing the spine. T. rex also likely had specialized pads on the soles of its feet like elephants today to feel low frequencies in the ground to find and locate its prey like ceratopsians or ankylosaurs.

Another terrifying aspect about Tyrannosaurus rex was the size of its brain. It was the smartest of the large theropods, and its brain was about the size of a gorilla's or a coconut. Recent studies show that T. rex was probably about as smart as a lion, meaning this dinosaur could use strategic thinking to take down tough prey like Triceratops and Ankylosaurus. T. rex probably became so smart because unlike other large theropods, which hunted large, small-brained sauropods, it hunted tough animals that were about the same size, like Triceratops, so it would need to come up with a plan to kill it. That can also explain why the teeth were so much broader, thicker, and stronger than other carnivores, since there was more armor that needed to be bitten through. This brain size may also have led T. rex to be able to form a family pack, letting the juveniles chase after the prey items into the jaws of the adults, like lions do today. Hunting in packs or pairs could also be a factor in being able to take down tough prey. If T. rex hunted in a pack, most likely the juveniles would chase the prey towards the more powerful adults, where they would kill it. If it hunted in pairs, they probably attacked together on each side. If it was alone, then the tyrannosaur probably waited until it was ready to attack, and then would charge and repeatedly bite down until thge prey became weak and died. The large brain also helped T. rex take better care of its young, so the next generation of killers had a greater chance of surviving. The skull of T. rex also shows that it had large eyes that faced forward, giving it three-dimensional binocular vision, while most theropods had eyes that were on the sides of their heads. Considering how large its eyes were and how good of a sense of smell it had, there's also been debate as to whether Tyrannosuarus was a part-time nocturnal hunter.

== Taxonomy ==
File:Tyrannosaurus Sue.JPG
For a long time T. rex was considered part of the carnosaur genus, like Allosaurus, but a closer analysis a few years ago showed that it was actually part of its own genus; the tyrannosaurids, which descended from coelurosaurs like Velociraptor. While Tyrannosaurus was by far the biggest tyrannosaurid, it wasn't the only one. It had numerous relatives; Daspletosaurus, Albertosaurus, and Tarbosaurus are all part of the tyrannosaur family. The earliest known tyrannosaurs were actually small hunters from the Jurassic Period, like Guanlong. Of all it's relatives, Daspletosaurus is believed to be the direct ancestor of T. rex, due to its very similar appearance. The skull of a small tyrannosaur, Nanotyrannus, found in South Dakota, was later thought to be from an adolescent T. rex but it is still possibly a separate species or genus. T. rex had a relatively short neck for such a large theropod, but was very well muscled and designed to withstand much more force from its powerul bite than other theropods were. Although Tyrannosaurus rex was the peak of tyrannosaur and carnivourous dinosaur evolution, it was an evolutionary dead end, with its closest descendants being birds, because of the K-T Extinction caused by a massive asteroid or comet.

Of the 31 specimens found, the most famous, most complete, and largest T. rex skeleton on display is Sue, a 42 foot (13 m) long Tyrannosaurus found in the badlands of South Dakota in 1990 by Susan Hendrickson. Sue's the most complete skeleton of any tyrannosaur, and was auctioned off in Washington D.C. for over $8,000,000. The skeleton is now on display in the Field Museum in Chicago, Illinois for everyone to see, but its skull is on a seperate case because it was too heavy to put on the actual skeleton, so they made a lighter replica and put it on the frame instead. Sue was named after the paleontologist who found it, but scientists aren't quite sure what its gender is. Not only is Sue the most complete and largest displayed T. rex, but it's also the oldest, dying at the age of 28. This seems to suggest tyrannosaurs grew continuously as they aged. Sue has given the most information of any T. rex skeleton yet, and is one of only a few Tyrannosaurus with a complete skull and forelimb. Despite being so large and ferocious, Sue's bones have shown just how tough its life was. It has healed rib fractures, healed infected broken leg bones, bites taken out of its vertebrae by other tyrannosaurs, and even arthritis. Another significant specimen found by Dr. Jack Horner, curator of the Museum of the Rockies in Bozeman, Montana, shows medullary tissue in the bone sctructure, tissue only found in modern-day pregnant birds. This is a very significant find because it's the first dinosaur ever discovered to show that dinosaurs (or at least coelurosaurs) had a birth cycle much closer to birds than previously thought, and also shows the first proven male or female Tyrannosaurus. Some other famous T. rex specimens are Stan, Thomas, Samson, and Jane.

Popular Culture

  • Tyrannosaurus is possibly the most famous of dinosaurs, ever since its discovery in 1902, it's been extremely popular, and it's almost always the first dinosaur that comes to mind when the word "Dinosaur" is mentioned, being one of the only dinosaurs where nearly everyone actually fully knows its name.
  • It is shown in every single dinosaur movie involving dinosaurs barring Walking with Dinosaurs: The 3D Movie. Its first appearance in the movies was in the 1925 film The Lost World, where it battles an Agathaumas.
  • It also played an important role in the 1990 book and 1993 famous movie Jurassic Park.
  • It also appeared in the sequel to 1997 Jurassic Park The Lost World: Jurassic Park. In this movie it rampaged through San Diego in an attempt to find its offspring.
    File:Tyrannosaurus rex bites Spinosaurus.jpg.jpg
  • It later appeared in the 2001 third sequel of Jurassic Park Jurassic Park 3. Here a sub-adult male Tyrannosaurus ate the remains of a Parasaurolophus and was killed by a fully grown adult Spinosaurus.
  • It also starred in an episode of the reknown documentary series Walking With Dinosaurs, and two shows from the same producers called Prehistoric Park and Primeval.
  • It also appeared in several episodes of the well known documentary Jurassic Fight Club, Animal Armageddon, Dinosaurs Decoded, Truth About Killer Dinosaurs, T. rex: New Science, New Beast, Prehistoric Denver, Dino Gangs, Ultimate Guide: Tyrannosaurus rex, Last Day of the Dinosaurs, and Clash of the Dinosaurs.
  • Another documentary it's been in is Dinosaur Revolution, where it showed how a family of tyrannosaurs lived until the K-T Extinction.
  • File:Tyrannosaurus new.png
    A Tyrannosaurus named Heart serves as the main protaganist of the 2010 anime film You Are Umasou and as antagonists in the books and TV shows of Dinotopia.
  • It's also featured in many games involvong dinosaurs, including all Jurassic Park Games, all Dino Crisis Games, and also Primal Carnage. It has also been featured in the Fossil Fighters series, appearing on the cover of the seque, Fossil Fighters Champions. Tyrannosaurus appears in Turok, as there is a T. rex that has grown to intense size, as it is nicknamed "Mama Scarface", for the scar on its right eye.
  • It was also in the IMAX movie, T. rex: Back to the Cretaceous. A giant robotic Tyrannosaurus is piloted by the red ranger in both the Mighty Morphin' Power Ranger series and the Dino Thunder series.
  • Tyrannosaurus is also the antagonist of nearly every episode of The Land Before Time.
  • It also starred in a Hollywood parody called T. rex: A Dinosaur in Hollywood, where they talk about how T. rex gained its fame throughout its discovery to modern-day movies, and also was in the Disney movie Fantasia where it fought a Stegosaurus while the song "The Rite of Spring" played.
  • It was also a main source for evolution in many episodes of the History Channel show Evolve.
  • It also served as the main dinosaur in a documentary called Tyrannosaurus Sex, where they talked
    File:Tyrannasaurus Spitter.gif
    about how T. rex and other dinosaurs may have reproduced.
  • Tyrannosaurus was also an antagonist in the comedy movie Land of the Lost and the Korean film Speckles: the Tarbosaurus, where it was named "One Eye" and killed the family of the main character "Speckles", a Tarbosaurus.
  • Jack Horner also talked about T. rex and why he believes it's mostly a scavenger in Valley of the T. rex.
  • Tyrannosaurus also made a short cameo in Dinosaur Planet.
  • A T. rex named Rex is the main protagonist of We're Back! A Dinosaur's Story
  • T. rex is one of the main dinosaurs in the Dinosaur themed restaurant T-Rex Cafe located in Disney World and Kansas City. It's mascot is also a T. rex named Dexter.
  • File:T-Rex 3.png
    A T.rex named Grumpy by the characters appeared in the 2009 film Land of the Lost.
  • Tyrannosaurus rex is seen as The Disneyland train travels to the Primeval World diorama. In it, he is seen reenacting his battle from Fantasia.
  • In Walt Disney World's Epcot there is a ride known as Ellen's Energy Adventure staring Ellen DeGeneres and Bill Nye the Science Guy, who explore the world of energy, including the use of fossil fuels. During the ride, Bill Nye brings DeGeneres "back in time" to the age of dinosaurs to explain the origin of fossil fuels. During this portion of the ride, several dinosaurs can be seen that are similar to the ones during Fantasia's The Rite of Spring. Most notably, there is a large Tyrannosaurus attacking a Stegosaurus over a cliff. This is obviously in reference to Fantasia. At Downtown Disney's T-Rex Cafe, there is a large Tyrannosaurus with his young.It is even in jurrassic fight club a dinosaur documentry .



Websites: (Username: University Password: Trojans)


Walking with Dinosaurs Walking With Beasts

Dinosaur Revolution

Clash of the Dinosaurs

T. rex: New Science, New Beast

Prehistoric Park

Jurassic Fight Club

Dinosaurs Decoded

The Truth About Killer Dinosaurs

Animal Armageddon


Dino Gangs

Ultimate Guide: Tyrannosaurus rex

Prehistoric Park

The Last Days Of The Dinosaurs

Tyrannosaurus Sex

T. rex: Back to the Cretaceous

T. rex: A Dinosaur in Hollywood


Prehistoric Denver

Valley of the T. rex

T. rex: Warrior or Wimp?

Bizarre Dinosaurs

Dinosaurs Unearthed

Dinosaur 13


The Complete Guide To Prehistoric life ;by Tim Haines and Paul Chambers

Ultimate Book of Dinosaurs; by Paul Dowswell, John Malam, Paul Mason, Steve Parker

Dino Wars; by Jinny Johnson, consulted by Michael J. Benton

Vertebrate Paleontology; by Michael J. Benton

How do We Know Dinosaurs Existed; by Mike Benton

The Audubon Society Pocket Guides Familiar Dinosaurs; by Alfred A. Knopf

Uncover T. rex; by Dennis Schaz

The Dinosaur Heresies; by Robert T. Bakker

Life-Sized Dinosaurs; David Bergen

Rise and Fall of the Dinosaur; Joseph Wallace

Tyrannosaurus Sue; Steve Fiffer

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