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Tyrannosaurus

2007 Schools Wikipedia Selection. Related subjects: Dinosaurs

             iTyrannosaurus

                        Fossil range: Late Cretaceous

   Fossil skeleton atNational Museum of Natural History, Washington, D.C.
   Fossil skeleton at
   National Museum of Natural History, Washington, D.C.

                             Conservation status

   Extinct (fossil)
                         Scientific classification

   Kingdom:    Animalia
   Phylum:     Chordata
   Class:      Sauropsida
   Superorder: Dinosauria
   Order:      Saurischia
   Suborder:   Theropoda
   Family:     Tyrannosauridae
   Subfamily:  Tyrannosaurinae
   Genus:      Tyrannosaurus
   Species:    T. rex

                                Binomial name

   Tyrannosaurus rex
   Osborn, 1905

                                  Synonyms

   Manospondylus gigas
   Dynamosaurus imperiosus
   Dinotyrannus megagracilis
   Nanotyrannus lancensis?

   Tyrannosaurus ( IPA pronunciation /taɪˌɹænəˈsɔrəs/ or /tɪ-/; from the
   Greek "τυραννόσαυρος", meaning 'tyrant lizard') is a genus of
   tyrannosaurid theropod dinosaur. The species Tyrannosaurus rex,
   commonly abbreviated to T. rex, is one of the dinosaurs most often
   featured in popular culture around the world. It hails from what is now
   western North America. Some scientists consider the slightly older
   Tarbosaurus bataar from Asia to represent a second species of
   Tyrannosaurus, while others maintain Tarbosaurus as a separate genus.

   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 and retained
   only two digits. 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 over 12  metres (40  feet) in length
   and weighing as much as an elephant.

   Fossils of some T. rex have been found in North American rock
   formations dating to the very end of the Cretaceous Period (late
   Maastrichtian stage, 65 million years ago); it was among the last
   dinosaurs to exist prior to the Cretaceous-Tertiary extinction event.
   More than 30 specimens of T. rex have now been identified, some nearly
   complete, which has allowed significant research into many aspects of
   its biology, including its life history and biomechanics. The feeding
   habits and potential speed of T. rex remain controversial.

Description

   The size of Tyrannosaurus, compared with a 1.8 m (approx. 6 ft) human
   Enlarge
   The size of Tyrannosaurus, compared with a 1.8 m (approx. 6 ft) human

   Tyrannosaurus rex was one of the largest land carnivores of all time,
   about 12 to 13  meters (40 to 43.3  feet) long, and 4.5-5 m (14-16 ft)
   tall, when fully-grown. Mass estimates have varied widely over the
   years, from more than 7,200  kilograms (8  short tons), to less than
   4,500 kg (5 tons), with most modern estimates ranging between 5,400 and
   6,800 kg (between 6 and 7.5 tons).

   The largest known T. rex skulls measure up to 1.5 m (5 ft) in length.
   Compared to other theropods, the skull was heavily modified. The skull
   was extremely wide posteriorly, with a narrow snout, allowing some
   degree of binocular vision. Some of the bones, such as the nasals, were
   fused, preventing movement between them. Large fenestrae (openings) in
   the skull reduced weight and provided areas for muscle attachment. The
   bones themselves were massive, as were the serrated teeth which, rather
   than being bladelike, were oval in cross-section. Like other
   tyrannosaurids, T. rex displayed marked heterodonty, with the
   premaxillary teeth at the front of the upper jaw closely-packed and
   D-shaped in cross-section. Large bite marks found on bones of other
   dinosaurs indicate that these teeth could penetrate solid bone. T. rex
   had the greatest bite force of any animal. Worn or broken teeth are
   often found, but unlike those of mammals, tyrannosaurid teeth were
   continually replaced throughout the life of the animal.

   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
   two-fingered forelimbs were very small relative to the size of the
   body, but heavily built. In contrast, the hindlimbs 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. This
   reduced the weight of the skeleton while maintaining much of the
   strength of the bones.

Classification

   T. rex head reconstruction at the Oxford University Museum of Natural
   History
   Enlarge
   T. rex head reconstruction at the Oxford University Museum of Natural
   History

   Tyrannosaurus is the type genus of the superfamily Tyrannosauroidea,
   the family Tyrannosauridae, and the subfamily Tyrannosaurinae. 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. However, 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. However, these fossils are now
   universally considered to belong to juvenile T. rex. A small but nearly
   complete skull from Montana, 60 cm (2 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.

Manospondylus controversy

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

   Controversy erupted in June 2000 after more tyrannosaur bones unearthed
   in South Dakota by the Black Hills Institute were found at the type
   locality of M. gigas and judged to represent further remains of the
   same individual. These more recently-discovered remains clearly belong
   to T. rex. According to the rules of the International Commission on
   Zoological Nomenclature, the system that governs the scientific naming
   of animals, Manospondylus gigas should therefore have priority over
   Tyrannosaurus rex, because it was named first. However, in the Fourth
   Edition of the International Code of Zoological Nomenclature, which
   took effect on January 1, 2000, Chapter 6, Article 23.9 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
   more than qualifies as the valid name under these conditions and is
   considered a nomen protectum ("protected name") under the ICZN, making
   Manospondylus gigas a nomen oblitum ("forgotten name").

Paleobiology

   As with all dinosaurs known only from the fossil record, much of
   Tyrannosaurus biology, including behaviour, coloration, ecology, and
   physiology, remains unknown. However, many new specimens have been
   discovered in the last twenty years, which has allowed some informed
   speculation on growth patterns, sexual dimorphism, biomechanics, and
   metabolism.

Life history

   A graph showing the hypothesized growth curves (body mass versus age)
   of four tyrannosaurids. Tyrannosaurus rex is drawn in black. Based on
   Erickson et al. 2004
   Enlarge
   A graph showing the hypothesized growth curves (body mass versus age)
   of four tyrannosaurids. Tyrannosaurus rex is drawn in black. Based on
   Erickson et al. 2004

   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 so-called "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 (1600 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).
   This sudden change in slope of the growth curve 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. 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 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, similarly 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.
   Outdated reconstruction (by Charles R. Knight), showing 'tripod' pose
   Enlarge
   Outdated reconstruction (by Charles R. Knight), showing 'tripod' pose

   It was also thought that 'robust' animals possessed a reduced chevron
   on the first tail vertebra, also ostensibly to allow eggs to pass out
   of the reproductive tract, as had been reported for crocodiles.
   However, in recent years, evidence for sexual dimorphism has been
   weakened. 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. In 2005, it
   was reported that crocodiles exhibited no sexual dimorphism in chevron
   anatomy either, further weakening the case for dimorphism between T.
   rex sexes. As T. rex specimens have been found from Saskatchewan to New
   Mexico, differences between individuals may be more 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," the geologically oldest
   known specimen, 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. The presence of
   medullary tissue also provides further evidence of the close
   evolutionary relationship between birds and theropod dinosaurs.

Posture

   Replica at Senckenberg Museum, showing modern view of posture
   Enlarge
   Replica at Senckenberg Museum, showing modern view of posture

   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. Despite its inaccuracies, the
   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. There have been
   suggestions that, when chasing prey, the animal might have raised its
   neck into an 'S' position (much like that of a bird) in order to avoid
   problems in changing direction; this was discussed in The Truth About
   Killer Dinosaurs. This way, the head might not always have been jutting
   forwards.

Arms

   Closeup of forelimb; specimen at National Museum of Natural History,
   Washington, DC
   Enlarge
   Closeup of forelimb; specimen at National Museum of Natural History,
   Washington, DC

   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 m (3 ft 3 in) 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 kg (438 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.

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
   body covering is consistent with modern multi-ton animals such as
   elephants, hippopotamus, and most species of rhinoceros, all of which
   lack hair over most of their bodies. As animals increase in size, their
   ability to retain heat increases due to their decreasing surface
   area-to- volume ratios. 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. Some scientists
   speculate that young tyrannosaurs may have had a feathery down, similar
   to modern bird chicks, but this is purely guesswork.

Tyrannosaurus warm-blooded?

   Tyrannosaurus has been at the centre of the warm-blooded versus
   cold-blooded debate ever since its beginnings with the paleontologist
   Robert T. Bakker. Like many other theropods, Tyrannosaurus is thought
   to have been warm-blooded due to its heightened levels of activity. To
   have been able to capture prey actively for example, it would have been
   useful to the creature to be warm-blooded. T. rex also has anatomical
   features distinctly similar to birds, which are warm-blooded. However,
   since the birth of the theory that Tyrannosaurus was in fact a
   scavenger, the theory that Tyrannosaurus was warm-blooded has been cast
   into doubt. Although Bakker provided some important factual evidence,
   paleontologists are still divided on the issue.

Feeding strategies

   Tyrannosaurus rex skull and upper vertebral column, Palais de la
   Découverte, Paris
   Enlarge
   Tyrannosaurus rex skull and upper vertebral column, Palais de la
   Découverte, Paris

   Most debate about Tyrannosaurus centers on its feeding patterns and
   locomotion. One paleontologist, noted hadrosaur expert Jack Horner,
   claims that Tyrannosaurus was exclusively a scavenger and did not
   engage in active hunting at all. Horner has only presented this in an
   official scientific context once, while mainly discussing it in his
   books and in the media. His hypothesis is based on the following:
   Tyrannosaurs have large olfactory bulbs and olfactory nerves (relative
   to their brain size). These suggest a highly developed sense of smell,
   allegedly used to sniff out carcasses over great distances. Tyrannosaur
   teeth could crush bone, a skill perhaps used to extract as much food (
   bone marrow) as possible from carcass remnants, usually the least
   nutritious parts. Since at least some of Tyrannosaurus's prey could
   move quickly, evidence that it walked instead of ran could indicate
   that it was a scavenger.

   Most scientists who have published on the subject since insist that
   Tyrannosaurus was both a predator and a scavenger, taking whatever meat
   it could acquire depending on the opportunity that was presented.
   Modern carnivores such as lions and hyenas will often scavenge what
   other predators have killed, suggesting that tyrannosaurs may also have
   done so.

   Some other evidence exists that suggests hunting behaviour in
   Tyrannosaurus. The ocular cavities of tyrannosaurs are positioned so
   that the eyes would point forward, giving the dinosaur binocular
   vision. A scavenger might not need the advanced depth perception that
   stereoscopic vision affords; in modern animals, binocular vision is
   found primarily in predators.
   T. rex right hind foot (medial view) Oxford University Museum of
   Natural History
   Enlarge
   T. rex right hind foot (medial view) Oxford University Museum of
   Natural History

   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, it might
   be strong evidence for aggressive behaviour between tyrannosaurs but
   whether it would be 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. In
   the Sue excavation site, an Edmontosaurus annectens skeleton was also
   found with healed tyrannosaur-inflicted scars on its tail. The fact
   that the scars seem to have healed suggests active predation instead of
   scavenging a previous kill. Another piece of evidence is a Triceratops
   found with bite marks on its ilium. Again, these were inflicted by a
   tyrannosaur and they too appear healed.

   For all intents and purposes, the 'scavenging debate' does not actually
   exist in any scientific context. However, there have been conflicting
   studies regarding the extent to which Tyrannosaurus could run and
   exactly how fast it might have been; speculation has suggested speeds
   up to 70 km/h (45 mph) or even more. However, according to James
   Farlow, a palaeontologist at Indiana-Purdue University in Fort Wayne,
   Indiana, "If T. rex had been moving fast and tripped, it would have
   died." If it tripped and fell while running, a tumbling tyrannosaur's
   torso would have slammed into the ground at a deceleration of 6g (six
   times the acceleration due to gravity, or about 60 m/s²). See
   Locomotion, below.

   Some argue that if Tyrannosaurus were a scavenger, another dinosaur had
   to be the top predator in the Amerasian Upper Cretaceous. Top prey were
   the larger marginocephalians and ornithopods. The other tyrannosaurids
   share so many characteristics that only small dromaeosaurs 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.

Locomotion

   T. rex right hind foot (lateral) Oxford University Museum of Natural
   History
   Enlarge
   T. rex right hind foot (lateral) Oxford University Museum of Natural
   History

   Scientists who think that Tyrannosaurus was able to run slowly point
   out that hollow Tyrannosaur 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 km/h or 25–45 mph).

   Some old studies of leg anatomy and living animals suggested that
   Tyrannosaurus could not run at all and merely walked. The ratio of
   femur (thigh bone) to tibia (shank bone) length (greater than 1, as in
   most large theropods) could indicate that Tyrannosaurus was a
   specialized walker, like a modern elephant. In addition, it had tiny
   'arms' that could not have stopped the dinosaur's fall, had it stumbled
   while running; standard estimates of Tyrannosaurus weight at 6 to
   8 tons would produce a lethal impact force, should it have fallen. It
   should be noted, however, that giraffes have been known to gallop at
   50 km/h (31 mph). At those speeds, the animal risks breaking a leg or
   worse, which can be fatal even when the accident occurs in a 'safe'
   environment, such as a zoo. If it could run, Tyrannosaurus may have
   been a risk-taker, in much the same way as animals alive today are. Yet
   estimates of leg bone strength in Tyrannosaurus show that its legs were
   little, if any stronger, than those of elephants, which are relatively
   limited in their top speed and do not ever become 'airborne', as would
   happen in running.

   Walking proponents estimate the top speed of Tyrannosaurus at about
   17 km/h (11 mph). This is still faster than the most likely prey
   species that co-existed with tyrannosaurs; the hadrosaurs and
   ceratopsians. In addition, some predation advocates claim that
   tyrannosaur running speed is not important, since it may have been slow
   but better designed for speed than its probable prey or it may have
   used ambush tactics to attack faster prey animals.
   T. rex mounted skeleton(Oxford University Museum of Natural History)
   Enlarge
   T. rex mounted skeleton
   ( Oxford University Museum of Natural History)

   The most recent research on Tyrannosaurus locomotion does not specify
   how fast Tyrannosaurus may have run, but admits that there is little
   capacity to narrow down speeds further than a range from 17 km/h
   (11 mph), which would be only walking or slow running, to 40 km/h
   (25 mph), which would be moderate-speed running. For example, a paper
   in Nature used a mathematical model (validated by applying it to two
   living animals, alligators and chickens) to gauge the leg muscle mass
   needed for fast running (over 25 mph / 40 km/h). They found that
   proposed top speeds in excess of 40 km/h (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 were. If they were
   smaller, only ~11 mph (18 km/h) walking/jogging might have been
   possible.

History

   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.

Earliest finds

   The vertebrae named Manospondylus by Cope in 1892 can be considered the
   first known specimen of Tyrannosaurus rex. Barnum Brown, assistant
   curator of the American Museum of Natural History, found the second
   Tyrannosaurus skeleton in Wyoming in 1900. This specimen was originally
   named Dynamosaurus imperiosus in the same paper in which Tyrannosaurus
   rex 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, London.
   Scale model of the never-completed Tyrannosaurus rex exhibit planned
   for the American Museum of Natural History by H.F. Osborn
   Enlarge
   Scale model of the never-completed Tyrannosaurus rex exhibit planned
   for the American Museum of Natural History by H.F. Osborn

   In total, Barnum Brown found five Tyrannosaurus partial skeletons.
   Brown collected his second Tyrannosaurus in 1902 and 1905 in Hell
   Creek, Montana. This is the holotype used to describe Tyrannosaurus rex
   Osborn, 1905. In 1941 it 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.

Named skeletons

   Another Tyrannosaurus, nicknamed "Stan", in honour 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.
   Sue the Tyrannosaurus, Field Museum of Natural History, Chicago,
   showing the forelimbs. The 'wishbone' is between the forelimbs.
   Enlarge
   Sue the Tyrannosaurus, Field Museum of Natural History, Chicago,
   showing the forelimbs. The 'wishbone' is between the forelimbs.

   Susan 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
   August 12, 1990. This Tyrannosaurus, now named "Sue" in her honor, was
   the object of a legal battle over its ownership. In 1997 this was
   settled in favour of Maurice Williams, the original land owner, and the
   fossil collection was sold at auction for USD 7.6 million. It has now
   been reassembled and is currently exhibited at the Field Museum of
   Natural History. Based on a study of 'her' fossilized bones, Sue died
   at 28 years of age, having reached full size at 19 years of age.
   Researchers report that a subadult and a juvenile skeleton were found
   in the same quarry as Sue; this lends evidence to the possibility that
   tyrannosaurs ran in packs or other groups.

   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.

   Also in 2001, Dr. Jack Horner discovered a specimen of T. rex around
   15% larger than "Sue". Dubbed C. rex (or "Celeste" after Jack's wife),
   this specimen is currently under study.

Latest news

   In the March 2005 Science magazine, 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.

   In a press release on April 7, 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%.

Appearances in popular culture

   Since it was first described in 1905, Tyrannosaurus has become the most
   widely-recognized dinosaur in popular culture. It is the only dinosaur
   which is commonly referred to by its scientific name, Tyrannosaurus
   rex, among the general public, and the scientific abbreviation T. rex
   (often mistakenly spelled "T-Rex") has also come into wide usage.
   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 movies, notably The Lost World, King Kong, Jurassic Park, and
   The Land Before Time. A number of books and comic strips, including
   Calvin and Hobbes, have also featured Tyrannosaurus, which is typically
   portrayed as the biggest and most terrifying carnivore of all (with the
   exception of Dinosaurs where the character Roy is portrayed as
   dim-witted and barely able to chew a lunch that's already accepted its
   fate as food). At least one musical group, the band T. Rex, is named
   after the species, as is The Hives' third album, Tyrannosaurus Hives.
   Tyrannosaurus-related toys, video games, and other merchandise remain
   popular. Various businesses have capitalized on the popularity of
   Tyrannosaurus rex by using it in advertisements.
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