Tyrannosaurus (pronounced /tɨˌrænəˈsɔːrəs/ or /taɪˌrænoʊˈsɔːrəs/, meaning 'tyrant lizard') is a genus of theropod dinosaur. The famous species Tyrannosaurus rex ('rex' meaning 'king' in Latin), commonly abbreviated to T. rex, is a fixture in popular culture around the world, and is extensively used in scientific television and movies, such as documentaries and Jurassic Park, and in children's series such as The Land Before Time. Tyrannosaurus lived throughout what is now western North America, with a much wider range than other tyrannosaurids. Fossils of T. rex are found in a variety of rock formations dating to the last three million years of the Cretaceous Period, approximately 68 to 65 million years ago; it was among the last non-avian dinosaurs to exist prior to the Cretaceous–Tertiary extinction event.
Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small, though unusually powerful for their size, and bore two primary digits, along with a possible third vestigial digit. Although other theropods rivaled or exceeded T. rex in size, it was the largest known tyrannosaurid and one of the largest known land predators, measuring up to 13 metres (43 ft.) in length, up to 4 metres (13 ft.) tall at the hips, and up to 6.8 metric tonnes (7.5 short tons) in weight. By far the largest carnivore in its environment, T. rex may have been an apex predator, preying upon hadrosaurs and ceratopsians, although some experts have suggested it was primarily a scavenger.
More than 30 specimens of T. 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 life history and biomechanics. The feeding habits, physiology and potential speed of T. rex are a few subjects of debate. Its taxonomy is also controversial, with some scientists considering Tarbosaurus bataar from Asia to represent a second species of Tyrannosaurus and others maintaining Tarbosaurus as a separate genus. 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, 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.
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.
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").
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.
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. 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.
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. 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
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, rare skin impressions from adult tyrannosaurids in Canada and Mongolia show pebbly scales typical of other dinosaurs. 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. 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.
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.
Two isolated fossilized footprints have been tentatively assigned to Tyrannosaurus rex. The first was discovered at Philmont Scout Ranch, New Mexico, in 1983 by American geologist Charles Pillmore. Originally thought to belong to a hadrosaurid, examination of the footprint revealed a large 'heel' unknown in ornithopod dinosaur tracks, and traces of what may have been a hallux, the dewclaw-like fourth digit of the tyrannosaur foot. The footprint was published as the ichnogenus Tyrannosauripus pillmorei in 1994, by Martin Lockley and Adrian Hunt. Lockley and Hunt suggested that it was very likely the track was made by a Tyrannosaurus rex, which would make it the first known footprint from this species. The track was made in what was once a vegetated wetland mud flat. It measures 83 centimetres (33 in) long by 71 centimetres (28 in) wide.
A second footprint that may have been made by a Tyrannosaurus was first reported in 2007 by British paleontologist Phil Manning, from the Hell Creek Formation of Montana. This second track measures 76 centimetres (30 in) long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by Tyrannosaurus is unclear, though Tyrannosaurus and Nanotyrannus are the only large theropods known to have existed in the Hell Creek Formation. Further study of the track (a full description has not yet been published) will compare the Montana track with the one found in New Mexico.
There are two main issues concerning the locomotory abilities of Tyrannosaurus: how well it could turn; and what its maximum straight-line speed was likely to have been. Both are relevant to the debate about whether it was a hunter or a scavenger (see below).
Tyrannosaurus may have been slow to turn, possibly taking one to two seconds to turn only 45°—an amount that humans, being vertically oriented and tail-less, can spin in a fraction of a second. The cause of the difficulty is rotational inertia, since much of Tyrannosaurus’ mass was some distance from its center of gravity, like a human carrying a heavy timber—although it might have reduced the average distance by arching its back and tail and pulling its head and forelimbs close to its body, rather like the way ice skaters pull their arms closer in order to spin faster.
Scientists have produced a wide range of maximum speed estimates, mostly around 11 metres per second (25 mph), but a few as low as 5–11 metres per second (11–25 mph), and a few as high as 20 metres per second (45 mph). Researchers have to rely on various estimating techniques because, while there are many tracks of very large theropods walking, so far none have been found of very large theropods running—and this absence may indicate that they did not run. Scientists who think that Tyrannosaurus was able to run point out that hollow bones and other features that would have lightened its body may have kept adult weight to a mere 5 tons or so, or that other animals like ostriches and horses with long, flexible legs are able to achieve high speeds through slower but longer strides. Additionally, some have argued that Tyrannosaurus had relatively larger leg muscles than any animal alive today, which could have enabled fast running 40–70 kilometres per hour (25–43 mph).
Jack Horner and Don Lessem argued in 1993 that Tyrannosaurus was slow and probably could not run (no airborne phase in mid-stride), because its ratio of femur (thigh bone) to tibia (shin bone) length was greater than 1, as in most large theropods and like a modern elephant. However, Holtz (1998) noted that tyrannosaurids and some closely related groups had significantly longer distal hindlimb components (shin plus foot plus toes) relative to the femur length than most other theropods), and that tyrannosaurids and their close relatives had a tightly interlocked metatarsus that more effectively transmitted locomotory forces from the foot to the lower leg than in earlier theropods ("metatarsus" means the foot bones, which function as part of the leg in digitigrade animals). He therefore concluded that tyrannosaurids and their close relatives were the fastest large theropods.
Christiansen (1998) estimated that the leg bones of Tyrannosaurus were not significantly stronger than those of elephants, which are relatively limited in their top speed and never actually run (there is no airborne phase), and hence proposed that the dinosaur's maximum speed would have been about 11 metres per second (25 mph), which is about the speed of a human sprinter. But he also noted that such estimates depend on many dubious assumptions.
Farlow and colleagues (1995) have argued that a 6 short tons (5.4 t) to 8 short tons (7.3 t) Tyrannosaurus would have been critically or even fatally injured if it had fallen while moving quickly, since its torso would have slammed into the ground at a deceleration of 6 g (six times the acceleration due to gravity, or about 60 meters/s²) and its tiny arms could not have reduced the impact. However, giraffes have been known to gallop at 50 kilometres per hour (31 mph), despite the risk that they might break a leg or worse, which can be fatal even in a "safe" environment such as a zoo. Thus it is quite possible that Tyrannosaurus also moved fast when necessary and had to accept such risks.
Most recent research on Tyrannosaurus locomotion does not narrow down speeds further than a range from 17 to 40 kilometres per hour (11 to 25 mph), i.e. from walking or slow running to moderate-speed running. For example, a 2002 paper in the journal Nature used a mathematical model (validated by applying it to three living animals, [alligators, chickens, and humans; additionally later eight more species including emus and ostriches) to gauge the leg muscle mass needed for fast running (over 40 kilometres per hour (25 mph)). They found that proposed top speeds in excess of 40 kilometres per hour (25 mph) were unfeasible, because they would require very large leg muscles (more than approximately 40–86% of total body mass.) Even moderately fast speeds would have required large leg muscles. This discussion is difficult to resolve, as it is unknown how large the leg muscles actually were in Tyrannosaurus. If they were smaller, only 18 kilometres per hour (11 mph) walking/jogging might have been possible.
A study in 2007 used computer models to estimate running speeds, based on data taken directly from fossils, and claimed that T. rex had a top running speed of 8 metres per second (18 mph). An average professional football (soccer) player would be slightly slower, while a human sprinter can reach 12 metres per second (27 mph). Note that these computer models predict a top speed of 17.8 metres per second (40 mph) for a 3 kilograms (6.6 lb) Compsognathus (probably a juvenile individual).
Those who argue that Tyrannosaurus was incapable of running estimate the top speed of Tyrannosaurus at about 17 kilometres per hour (11 mph). This is still faster than its most likely prey species, hadrosaurids and ceratopsians. In addition, some advocates of the idea that Tyrannosaurus was a predator claim that tyrannosaur running speed is not important, since it may have been slow but still faster than its probable prey. However, Paul and Christiansen (2000) argued that at least the later ceratopsians had upright forelimbs and the larger species may have been as fast as rhinos. Healed Tyrannosaurus bite wounds on ceratopsian fossils are interpreted as evidence of attacks on living ceratopsians (see below). If the ceratopsians that lived alongside Tyrannosaurus were fast, that casts doubt on the argument that Tyrannosaurus did not have to be fast to catch its prey.
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 agreed that it was a predator, although like modern large predators it would have been happy to scavenge or steal another predator's kill if it had the opportunity.
Noted hadrosaur expert Jack Horner is currently the major advocate of the idea that Tyrannosaurus was exclusively a scavenger and did not engage in active hunting at all. Horner has presented several arguments to support the pure scavenger hypothesis:
- 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. 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 dung) 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. He also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is hard to see how 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 (the principal exceptions are primates, which need it for leaping from branch to branch).
At the site where the very large tyrannosaur named Sue was found, a skeleton of the hadrosaurid Edmontosaurus annectens was also found, 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. A Triceratops was found in Mexico with bite marks on its ilium. These were also inflicted by a tyrannosaur and they too appear healed, indicating active predation by the tyrannosaur. This is consistent with the results of a study in 2003 which found that Tyrannosaurus’ estimated bite force of 183,000 newtons (180 LT; 202 ST) to 235,000 newtons (231 LT; 259 ST) made a single T. rex very capable of killing a Triceratops horridus.. 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 was the larger marginocephalians and ornithopods. The other tyrannosaurids share so many characteristics that only small dromaeosaurs 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. Most paleontologists accept that Tyrannosaurus was both an active predator and a scavenger.
Henry Fairfield Osborn, president of the American Museum of Natural History, named Tyrannosaurus rex in 1905. The generic name is derived from the Greek words τυραννος (tyrannos, meaning "tyrant") and σαυρος (sauros, meaning "lizard"). Osborn used the Latin word rex, meaning "king", for the specific name. The full binomial therefore translates to "tyrant lizard king," emphasizing the animal's size and perceived dominance over other species of the time.
Teeth from what is now documented as a T. rex were found in 1874 by A. Lakes near Golden, Colorado. In the early 1890s, J. B. Hatcher collected postcranial elements in eastern Wyoming. The fossils were believed to be from a large species of Ornithomimus (O. grandis) but are now considered T. rex. Vertebral fragments found by E. D. Cope in western South Dakota in 1892 and named as Manospondylus gigas have also been reclassified as T. rex.
Barnum Brown, assistant curator of the American Museum of Natural History, found the first partial skeleton of T. rex in eastern Wyoming in 1900. H. F. Osborn originally named this skeleton Dynamosaurus imperiosus in a paper in 1905. Brown found another partial skeleton in the Hell Creek Formation in Montana in 1902. Osborn used this holotype to describe Tyrannosaurus rex in the same paper in which D. imperiosus was described. Had it not been for page order, Dynamosaurus would have become the official name. The original Dynamosaurus material resides in the collections of the Natural History Museum, in London.
In total, Brown found five Tyrannosaurus partial skeletons. In 1941, Brown's 1902 find was sold to the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. Brown's fourth and largest find, also from Hell Creek, is on display in the American Museum of Natural History, in New York.
Although there are numerous skeletons in the world, only one track has been documented — at Philmont Scout Ranch in northeast New Mexico. It was discovered in 1983 and identified and documented in 1994.
Sue Hendrickson, amateur paleontologist, discovered the most complete (more than 90%) and, until 2001, the largest, Tyrannosaurus fossil skeleton known in the Hell Creek Formation near Faith, South Dakota, on 12 August 1990. This Tyrannosaurus, nicknamed "Sue" in her honor, was the object of a legal battle over its ownership. In 1997 this was settled in favor of Maurice Williams, the original land owner, and the fossil collection was sold at auction for USD 7.6 million, making it the most expensive dinosaur skeleton to date. It has now been reassembled and is currently exhibited at the Field Museum of Natural History. A study of this specimen's fossilized bones showed that "Sue" reached full size at age 19 and died at age 28, the longest any tyrannosaur is known to have lived. The "Sue" specimen apparently died from a massive bite to the head, which could only have been inflicted by another tyrannosaur.
Another Tyrannosaurus, nicknamed "Stan", in honor of amateur paleontologist Stan Sacrison, was found in the Hell Creek Formation near Buffalo, South Dakota, in the spring of 1987. After 30,000 hours of digging and preparing, a 65% complete skeleton emerged. Stan is currently on display in the Black Hills Museum of Natural History Exhibit in Hill City, South Dakota, after an extensive world tour. This tyrannosaur, too, was found to have many bone pathologies, including broken and healed ribs, a broken (and healed) neck and a spectacular hole in the back of its head, about the size of a Tyrannosaurus tooth. Both Stan and Sue were examined by Peter Larson.
In the summer of 2000, Jack Horner discovered five Tyrannosaurus skeletons near the Fort Peck Reservoir in Montana. One of the specimens, dubbed "C. rex," was reported to be perhaps the largest Tyrannosaurus ever found.
In 2001, a 50% complete skeleton of a juvenile Tyrannosaurus was discovered in the Hell Creek Formation in Montana, by a crew from the Burpee Museum of Natural History of Rockford, Illinois. Dubbed "Jane the Rockford T-Rex," the find was initially considered the first known skeleton of the pygmy tyrannosaurid Nanotyrannus but subsequent research has revealed that it is more likely a juvenile Tyrannosaurus. It is the most complete and best preserved juvenile example known to date. Jane has been examined by Jack Horner, Pete Larson, Robert Bakker, Greg Erickson and several other renowned paleontologists, because of the uniqueness of her age. Jane is currently on exhibit at the Burpee Museum of Natural History in Rockford, Illinois.
In a press release on 7 April 2006, Montana State University revealed that it possessed the largest Tyrannosaurus skull yet discovered. Discovered in the 1960s and only recently reconstructed, the skull measures 59 inches (150 cm) long compared to the 55.4 inches (141 cm) of “Sue’s” skull, a difference of 6.5%.
Tyrannosaurus in The Land Before Time
In both the Land Before Time films and television series, Tyrannosaurus plays an important role in sequences involving predators,similar to the Jurassic Park T.rex. As is the case for all carnivorous dinosaurs in the series, though some others have more specific terms, the herbivorous characters refer to T. rexes as "Sharpteeth". Contrary to modern paleontological thought, the characters are portrayed with an upright posture, but have also been seen in the correct horizontal posture (either walking or running).Tyrannosaurus is also commonly used in fanfiction as well. In The Land Before Time, Tyrannosaurus' color scheme is plain and simple and are usually (depending on gender) dark okra, caper berry and olive green, with the hatchling's exception of a varifying from light blue and purple as seen from one of the franchises main lead characters, Chomper. Though however this could only imply to him since no other Tyrannosaurus hatchling has yet to appear in the franchise itself.
In the original 1988 theatrical hit, The Land Before Time, the main antagonist was a Tyrannosaurus. This character, referred to by the other characters as "Sharptooth", as though it were his given name, started off the use of the term for predatory dinosaurs in The Land Before Time films and TV series. Other Tyrannosaurus seen throughout the franchise run include:
- Chomper, a young Tyrannosaurus who first appears in The Land Before Time II: The Great Valley Adventure, when he was hatched by the main characters. He is one of only a few protagonistic Sharpteeth in the series; having become loyal to leaf-eating dinosaurs due to his early brought-on friendship with Littlefoot, Cera, Ducky, Petrie and Spike. Also appearing in The Land Before Time V: The Mysterious Island, he joins the main characters in the television series.
- Chomper's mother and father, to-date the only other protagonistic Sharpteeth besides their son in the series. Originally antagonists in The Great Valley Adventure, they promise not to hurt Littlefoot and the others at the end of The Mysterious Island, when Littlefoot saves Chomper from drowning in the "Big Water" (sea). They have not appeared since that film, although the character Ruby the Oviraptor reveals in the TV episode "The Hidden Canyon" that they gave her the responsibility to raise their son, before the two headed to the Great Valley.
- Red Claw, the primary antagonist in the television series; he is distinguishable due to a long red scar going down from his eye to his arm. Red Claw is assisted by two raptor cronies, Screech and Thud. The trio are all portrayed as being very vicious, and possibly even cannibalistic, as Chomper and Ruby frequently imply that even the other Sharpteeth who live in the Mysterious Beyond are afraid of them.
- "The Biggest, Meanest, Most Ferocious Sharptooth Ever", a name given to a legendary Sharptooth by the character Grandpa Longneck. In The Land Before Time VII: The Stone of Cold Fire, Grandpa tells the children a story of how, at least two or three generations before his, this sharptooth came and raided upon the Great Valley, only to be defeated by the Lone Dinosaur. Days later, a large rocky formation resembling a longneck (sauropod) rose from the ground; surrounding its neck was a ring of teeth, said to be from the Sharptooth the Lone Dinosaur had defeated.
- Others There are many other unnamed Tyrannosaurus, seen on occasion in the series. Most of these characters are minor, usually having only brief appearances in one film each. Some of these include the green Sharptooth who assists the Allosaurus in the climax of The Secret of Saurus Rock, the brown Sharptooth in The Land Before Time VIII: The Big Freeze that encounters the main characters multiple times through the film, and the three Sharpteeth that appear as antagonists in The Great Longneck Migration (though the former is said to be an Albertosaurus while the latter are Daspletosaurus, both of which are related to Tyrannosaurus).
Since it was first described in 1905, Tyrannosaurus rex has become the most widely recognized dinosaur in popular culture. It is the only dinosaur which is routinely referred to by its full scientific name (Tyrannosaurus rex) among the general public, and the scientific abbreviation T. rex has also come into wide usage (commonly misspelled "T-Rex"). Robert T. Bakker notes this in The Dinosaur Heresies and explains that a name like "Tyrannosaurus rex is just irresistible to the tongue."
Museum exhibits featuring T. rex are very popular; an estimated 10,000 visitors flocked to Chicago's Field Museum on the opening day of its "Sue" exhibit in 2003. T. rex has appeared numerous times on television and in films, notably (in chronological order) The Lost World, King Kong, The Land Before Time, the Jurassic Park films, Barney and Friends, Toy Story, Toy Story 2, Walking with Dinosaurs, and Night at the Museum, among many others. A number of books and comic strips, including Calvin and Hobbes and Dinosaur Comics, have also featured Tyrannosaurus, which is typically portrayed as the biggest and most terrifying carnivore of all. At least one musical group, the band T.Rex, is named after the species. Tyrannosaurus-related toys, including numerous video games and other merchandise, remain popular. Various businesses have capitalized on the popularity of Tyrannosaurus rex by using it in advertisements.
Tyrannosaurus rex is unique among dinosaurs in its place in modern culture; paleontologist Robert Bakker has called it "the most popular dinosaur among people of all ages, all cultures, and all nationalities". From the beginning, it was embraced by the public. Henry Fairfield Osborn billed it the greatest hunter to have ever walked the earth. He stated in 1905,
Tyrannosaurus gained widespread public attention on December 30, 1905, when the New York Times hailed T. rex as "the most formidable fighting animal of which there is any record whatever," the "king of all kings in the domain of animal life," "the absolute warlord of the earth," and a "royal man-eater of the jungle."  In 1906, Tyrannosaurus was dubbed the "prize fighter of antiquity" and the "Last of the Great Reptiles and the King of Them All."
In 1942, Charles R. Knight painted a mural incorporating Tyrannosaurus facing a Triceratops in the Field Museum of Natural History for the National Geographic Society, establishing the two dinosaurs as enemies in popular thought; paleontologist Phil Currie cites this mural as one of his inspirations to study dinosaurs. Bakker said of the imagined rivalry between Tyrannosaurus and Triceratops, "No matchup between predator and prey has ever been more dramatic. It’s somehow fitting that those two massive antagonists lived out their co-evolutionary belligerence through the very last days of the very last epoch of the Age of Dinosaurs."
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Brochu, Christopher A. and Richard A. Ketcham Osteology of Tyrannosaurus Rex: Insights from a Nearly Complete Skeleton and High-resolution Computed Tomographic Analysis of the Skull. 2003, Society of Vertebrate Paleontology, in Northbrook, Illinois.
- ↑ 2.0 2.1 2.2 Sue's vital statistics Sue at the Field Museum. Field Museum of Natural History.
- ↑ 3.0 3.1 3.2 3.3 Erickson, Gregory M., Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; & Brochu, Christopher A., 2004. Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs, from the Journal of Nature, vol. 430, issue 7001, pp. 772–775.
- ↑ Henderson, DM, 1999. Estimating the masses and centers of mass of extinct animals by 3-D mathematical slicing, from the Journal of Paleobiology, vol. 25, issue 1, pp. 88–106 .
- ↑ Anderson, JF and Hall-Martin AJ, Russell, Dale A. 1985. Long bone circumference and weight in mammals, birds and dinosaurs, from the Journal of Zoology, vol. 207, issue 1, pp. 53–61.
- ↑ 6.0 6.1 6.2 Bakker, Robert T., 1986. The Dinosaur Heresies. New York, Kensington Publishing, ISBN 0-688-04287-2
- ↑ 7.0 7.1 Farlow, James O., Smith MB, & Robinson, JM, 1995. Body mass, bone "strength indicator", and cursorial potential of Tyrannosaurus rex, from the Journal of Vertebrate Paleontology, vol. 15, issue 4, pp. 713–725. 
- ↑ Seebacher, Frank. 2001. A new method to calculate allometric length-mass relationships of dinosaurs, from the Journal of Vertebrate Paleontology, vol. 21, issue 1, pp. 51–60.
- ↑ Christiansen, Per & Fariña, Richard A., 2004. Mass prediction in theropod dinosaurs, from the Journal of Historical Biology, vol. 16, issues 2-4, pp. 85–92.
- ↑ dal Sasso, Cristiano and Maganuco, Simone; Buffetaut, Eric; & Mendez, Marcos A. 2005. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities, from the Journal of Vertebrate Paleontology vol. 25, issue 4, pp. 888–896. 
- ↑ Calvo, Jorge O., and Rodolfo Coria, 1998, December. New specimen of Giganotosaurus carolinii (Coria & Salgado, 1995), supports it as the as the largest theropod ever found, from the Journal of Gaia Revista de Geociências, vol. 15, pp. 117–122. 
- ↑ 12.0 12.1 Brent H. Breithaupt, Elizabeth H. Southwell and Neffra A. Matthews, (2005-10-18). "In Celebration of 100 years of Tyrannosaurus Rex: Manospondylus Gigas, Ornithomimus Grandis, and Dynamosaurus Imperiosus, the Earliest Discoveries of Tyrannosaurus Rex in the West", from the conference of the 2005 Salt Lake City Annual Meeting, . Book: Abstracts with Programs, vol. 37, issue 7, published by: the Geological Society of America, pp. 406. .
- ↑ Museum unveils world's largest T-rex skull (2006-04-07) Montana State University.
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- ↑ 15.0 15.1 Jaffe, Eric (2006-07-01). Sight for 'Saur Eyes: T. rex vision was among nature's best, from the Journal of Science , vol. 170, issue 1, page 3. 
- ↑ 2006, Fused and vaulted nasals of tyrannosaurid dinosaurs: Implications for cranial strength and feeding mechanics, from the Acta Palaeontologica Polonica, vol. 51, issue 3, pp. 435–454. Eric Snively, Donald M. Henderson, and Doug S. Phillips. 
- ↑ Erickson, G.M. Van Kirk, S.D.; Su, J.; Levenston, M.E.; Caler, W.E.; and Carter, D.R. 1996. Bite-force estimation for Tyrannosaurus rex from tooth-marked bones, from the Journal of Nature, vol. 382, pp. 706–708.
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- ↑ William David Lindsay Ride. International code of zoological nomenclature, Publisher: International Commission on Zoological Nomenclature, in London, 1999. ISBN 0-85301-006-4 Chapter: Article 23.9 – Reversal of Precedence .
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- ↑ James O. Farlow and M. K. Brett-Surman, The Complete Dinosaur, published by the Indiana University Press in Bloomington, 1999. pp. 474–490. ISBN 0-253-21313-4 Chapter: Oxygen isotopes in dinosaur bones. By Reese E. Barrick, Michael K. Stoskopf, and William J. Showers.
- ↑ James O. Farlow and M. K. Brett-Surman, The Complete Dinosaur, published by Indiana University Press in Bloomington, 1999. pp. 491–504. ISBN 0-253-21313-4 Chapter: A blueprint for giants: modeling the physiology of large dinosaurs, by Frank V. Paladino, James R. Spotila and Peter Dodson.
- ↑ David B. Weishampel, Peter Dodson and Halszka Osmólska The dinosauria University of California Press, in Berkeley, 2004. pp. 643–659. ISBN 0-520-24209-2 Chapter: Physiology of nonavian dinosaurs, by Anusuya Chinsamy, and Willem J. Hillenius.
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- ↑ Influence of rotational inertia on turning performance of theropod dinosaurs: clues from humans with increased rotational inertia, from the Journal of Experimental Biology, vol. 204, issue 22, pp. 3917–3926. Published by the Company of Biologists, . Written by David R. Carrier, Rebecca M. Walter and David V. Lee (2001-11-15).
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- ↑ Christiansen, P., Strength indicator values of theropod long bones, with comments on limb proportions and cursorial potential, from the Journal of Gaia, (1998), vol. 15, pp. 241–255. . ISSN 0871-5424
- ↑ The bigger they come, the harder they fall. J. Hecht. (1995-10-05). Published by NewScientist; page 18.
- ↑ Giraffe. WildlifeSafari.info.
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- ↑ 85.0 85.1 Hanna, Rebecca R., 2002. Multiple injury and infection in a sub-adult theropod dinosaur (Allosaurus fragilis) with comparisons to allosaur pathology in the Cleveland-Lloyd dinosaur quarry collection, from the Journal of Vertebrate Paleontology, vol. 22, issue 1, pp. 76–90. (catalogs the injuries of the Allosaurus known as "Big Al" - at least one was attributed to a fall.)
- ↑ Hutchinson, J.R., Biomechanical Modeling and Sensitivity Analysis of Bipedal Running Ability. II. Extinct Taxa, from the Journal of Morphology, vol. 262, issue 1, pp. 441–461. (2004). 
- ↑ Estimating dinosaur maximum running speeds using evolutionary robotics, from the Journal of Proc. R. Soc. B. Published by The Royal Society, (July 2007). . Written by Sellers, W.I., and Manning, P.L. (vol. 274, pp. 2711.
- ↑ T. rex 'would outrun footballer', by Seward, L. (2007-08-21). Publishing by BBCNews.
- ↑ Callison, G., and H. M. Quimby (1984) Tiny dinosaurs: Are they fully grown?, from the Journal of Vertebrate Paleontology, vol. 3 , pp. 200–209.
- ↑ 90.0 90.1 Manning P, Carpenter, Kenneth; & Larson, Peter E. Tyrannosaurus rex, the Tyrant King (Life of the Past), chapter 12, T. rex speed trap. Publisher: Indiana University Press, in Bloomington ,(2008), Pages 205-228. ISBN 0-253-35087-5
- ↑ Forelimb posture in neoceratopsian dinosaurs: implications for gait and locomotion, from the Journal of Paleobiology, vol. 26, issue 3, page 450, (September, 2000). . By Paul, G.S., and Christiansen, P.
- ↑ Lambe, L. B., 1917. "The Cretaceous theropodous dinosaur Gorgosaurus", from the Journal of Memoirs of the Geological Survey of Canada, vol. 100, pages 1–84.
- ↑ The fossil record of predation in dinosaurs, editors: Kowalewski, M. and Kelley, P.H. The Fossil Record of Predation, (2002) from the series of The Paleontological Society Papers, vol. 8, pp. 251–266. . By Farlow, J. O. and Holtz, T. R.
- ↑ 94.0 94.1 94.2 Horner, J.R. (1994), Steak knives, beady eyes, and tiny little arms (a portrait of Tyrannosaurus as a scavenger), from the Journal of The Paleontological Society Special Publication, vol. 7, pp. 157–164.
- ↑ T. rex goes on trial. By Amos, J., published by BBC. (2003-07-31).
- ↑ T. Rex brain study reveals a refined "nose". Calgary Herald (2008-10-28).
- ↑ Paul, G.S., Predatory Dinosaurs of the World, (1988). Published by Simon and Schuster, ISBN 0671619462
- ↑ Ruxton GD, Houston DC. Could Tyrannosaurus rex have been a scavenger rather than a predator? An energetics approach, from the Journal of Proceedings. Biological sciences / the Royal Society, vol. 270, issue 1516, pp. 731–3 (2003, April.) [url=http://journals.royalsociety.org/openurl.asp?genre=article&issn=0962-8452&volume=270&issue=1516&spage=731].
- ↑ (1998-06-18) A king-sized theropod coprolite, from the Journal of Nature, vol. 393, page 680. By Chin, K., Erickson, G.M. et al, . Summary at: Monastersky, R., "Getting the scoop from the poop of T. rex", from the Journal of Science News, vol. 153, issue 25, (1998-06-20), page: 391, .
- ↑ 100.0 100.1 Walters, Martin, Bloomsbury Illustrated Dictionary of Prehistoric Life (Bloomsbury Illustrated Dictionaries); publisher: Godfrey Cave Associates Ltd, (1995). ISBN 1-85471-648-4
- ↑ Erickson, GM, & Olson, KH, (1996). "Bite marks attributable to Tyrannosaurus rex: preliminary description and implications", from the Journal of Vertebrate Paleontology, vol. 16, issue 1, pp. 175–178.
- ↑ Carpenter, K., (1998), Evidence of predatory behavior by theropod dinosaurs, from the Journal of Gaia, vol. 15, pp. 135–144. .
- ↑ Denver W. Fowler, & Robert M. Sullivan, (2006), A ceratopsid pelvis with toothmarks from the Upper Cretaceous Kirtland Formation, New Mexico: evidence of late Campanian tyrannosaurid feeding behavior, from the Journal of the New Mexico Museum of Natural History and Science Bulletin, vol. 35, pp. 127–130. .
- ↑ Tanke, Darren H., and Currie, Philip J., (1998), Head-biting behavior in theropod dinosaurs: paleopathological evidence, from the Journal of Gaia, issue 15, pp. 167–184. . ISSN 0871-5424
- ↑ The First Tyrannosaurus Skeleton, 1905, published by Linda Hall, of the Library of Science, Engineering and Technology. .
- ↑ Osborn, H.F. (1905), "Tyrannosaurus and other Cretaceous carnivorous dinosaurs", from the Journal of the Bulletin of the American Museum of Natural History, vol. 21, pp. 259–265.
- ↑ Breithaup, BH, & Southwell EH, Matthews NA, (2006), "Dynamosaurus Imperiosus and the earliest discoveries of Tyrannosaurus Rex in Wyoming and the West", from the Journal of the New Mexico Museum of Natural History and Science Bulletin, vol. 35, pp. 257-258. .
- ↑ Footprint of a Giant. From the Online guide to the continental Cretaceous-Tertiary boundary in the Raton basin, Colorado and New Mexico. (United States Geological Survey.)
- ↑ Stokstad, E.,"Bone Study Shows T. rex Bulked Up With Massive Growth Spurt", from the Science journal, (13 August 2004), vol. 305, issue 5686, pp. 930–931. .
- ↑ Lessons From A Tyrannosaur: The Ambassadorial Role Of Paleontology, by Brochui, C.A., from the Palaios journal. Vol. 18, issue 6, (December, 2003). . Page: 475.
- ↑ "Dig pulls up five T. rex specimens", from BBC News (10th, October, 2000). .
- ↑ Currie, PJ Huru, JH, & Sabath, K, (2003). "Skull structure and evolution in tyrannosaurid dinosaurs" from the Journal of Acta Palaeontologica Polonica, vol. 48, issue 2, pp. 227-234 .
- ↑ Henderson, M, The origin, systematics, and paleobiology of Tyrannosauridae, edited by: Henderson, M, & published by: the Northern Illinois University Press, in Dekalb, Illinois, (In press). Chapter: Nano No More: The death of the pygmy tyrant
- ↑ Visit Jane the Dinosaur at the Burpee Museum, Rockford, Illinois.
- ↑ Museum unveils world's largest T-rex skull. .
- ↑ New Biggest T-rex Skull. . By Ryan, M.J.
- ↑ Guinness World Records 2003, Folkard, C. Publisher: Guinness World Records Ltd., 2002. page 90. ISBN 1892051176
- ↑ Bakker, Robert. Edited by Fiffer, S. Tyrannosaurus Sue (2000). Publisher: W. H. Freeman & Company, in New York ISBN 0-7167-4017-6 pp. xi-xiv Chapter: Prologue.
- ↑ 119.0 119.1 John "Jack" Horner and Don "Dino" Lessem, The Complete T. Rex (New York: Simon & Schuster, 1993), pages 58-62
- ↑ “Mining for Mammoths in the Badlands: How Tyrannosaurus Rex Was Dug Out of His 8,000,000 Year old Tomb,” The New York Times, December 3rd, 1905, page SM1.
- ↑ "The Prize Fighter of Antiquity Discovered and Restored," The New York Times December 30th, 1906, page 21.
- ↑ 122.0 122.1 Bakker, R.T. 1986. The Dinosaur Heresies. New York: Kensington Publishing, p. 240. On that page, Bakker has his own T. rex/Triceratops fight.
- Tyrannosauridae "Tree of Life" page, very comprehensive survey by major authority Tom Holtz.
- The secret of T. rex's colossal size: a teenage growth spurt The Guardian, 12 August 2004.
- Tyrannosaurus in the Dino Directory
- Sue's homepage
- Stan's homepage
- Unearthing Tyrannosaurus rex
- T.rex juvenile Jane
- NBCI's Taxonomy Browser
- Cretaceous Hell Creek Faunal Facies is an example of one tyrannosaur environment, in the Hell Creek Formation of Montana
- Bristol University study on bite forces of predators
- Museum of Unnatural Mystery – Bite force etc. of T. rex
- Stanford University on bite force of T. rex
- How Tyrannosaurus might have had sex
- Recent Discovery of Soft Tissue