'''Tyrannosaurus''' (
IPA pronunciation or , meaning 'tyrant lizard') is a
genus of
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 ''
Tarbosaurus bataar'' from
Asia to represent a second species of ''Tyrannosaurus'', while others maintain ''Tarbosaurus'' as a separate genus. Other species have also been described, but these were either concluded to be synonymous with ''Tyrannosaurus rex'' or removed from the genus.
[1]
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 they 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 up to approximately 13
metres (43
feet) in length and up to 6.8
metric tons (7.5
short tons) in weight.
Fossils of ''T. rex'' have been found in North American
rock formations dating to the last three million years of the
Cretaceous Period at the end of the
Maastrichtian stage, approximately 68.5 to 65.5
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 been identified, some of which are nearly complete skeletons. Some researchers have discovered soft tissue as well. 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 often subjects of debate.
Description
''Tyrannosaurus rex'' was one of the largest land carnivores of all time, measuring 12 to 13
meters (40 to 43.3
feet) long, and 4.5–5 m (14–16.6 ft) tall, when fully-grown.
[2] Mass estimates have varied widely over the years, from more than 7,200
kilograms (8 tons),
[3] to less than 4,500 kg (5 tons),
[4][5] with most modern estimates ranging between 5,400 and 6,800 kg (between 6 and 7.5 tons).
[6][7][8][9]
Various specimens of ''Tyrannosaurus rex'' with a human for scale.
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 dinosaur and one of the strongest bite forces 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
''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'',
[10][11] both of which have occasionally been synonymized with ''Tyrannosaurus''.
[12] 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.
[13]
In 1955,
Soviet paleontologist Evgeny Maleev named a new species, ''Tyrannosaurus bataar'', from
Mongolia.
[14] By 1965, this species had been renamed ''Tarbosaurus bataar''.
[15] 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.
[18] 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.
[19] However, these fossils are now universally considered to belong to juvenile ''T. rex''.
[20] 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,
[21] but was later referred to a new genus, ''
Nanotyrannus''.
[22] Opinions remain divided on the validity of ''N. lancensis''. Many paleontologists consider the skull to belong to a juvenile ''T. rex''.
[23] 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
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.
[25]
Controversy erupted in June 2000 after 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.
[26] However, the Fourth Edition of the
ICZN, which took effect on
January 1 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…"
[27] ''Tyrannosaurus rex'' easily qualifies 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").
[28]
Paleobiology
As with all dinosaurs known only from the
fossil record, much of ''Tyrannosaurus'' biology, including behavior, 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.
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.
[29]
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.
[30] This sudden change 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.
[31] Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes.
[32]
Over half of the known ''T. rex'' specimens appear to have died within six years of reaching sexual maturity, a pattern which is also seen in other tyrannosaurs and in some large, long-lived birds and mammals today. These species are characterized by high infant mortality rates, followed by relatively low mortality among juveniles. Mortality increases again following sexual maturity, partly due to the stresses of reproduction. One study suggests that the rarity of juvenile ''T. rex'' fossils is due in part to low juvenile mortality rates; the animals were not dying in large numbers at these ages, and so were not often fossilized. However, this rarity may also be due to the incompleteness of the
fossil record or to the bias of fossil collectors towards larger, more spectacular specimens.
Sexual dimorphism
As the number of specimens increased, scientists began to analyze the variation between individuals and discovered what appeared to be two distinct body types, or ''morphs'', 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 '.' 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.
[33] 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.
[34]
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.
[35] 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.
[36]
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.
[37] 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.
[38] 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.
[39] 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.
Arms
When ''Tyrannosaurus rex'' was first discovered, the
humerus was the only element of the forelimb known.
[40] 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''.
[41] 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").
[42] 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.
[43] 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.
[44]
Soft tissue
In the March 2005 issue of ''
Science'', Mary Higby Schweitzer of
North Carolina State University and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone, from a 68 million-year-old ''Tyrannosaurus''. The bone had been intentionally, though reluctantly, broken for shipping and then not preserved in the normal manner, specifically because Schweitzer was hoping to test it for soft tissue. Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the Hell Creek Formation. Flexible, bifurcating
blood vessels and fibrous but elastic
bone matrix tissue were recognized. In addition, microstructures resembling
blood cells were found inside the matrix and vessels. The structures bear resemblance to
ostrich blood cells and vessels. Whether an unknown process, distinct from normal fossilization, preserved the material, or the material is original, the researchers do not know, and they are careful not to make any claims about preservation.
[45] 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.
[46] Research on some of the tissues involved have suggested that birds are closer relatives to tyrannosaurs than other modern animals.
[47]
In subsequent 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."
[48]
Skin
Main articles: Feathered dinosaurs
A baby ''T. Rex'', covered with
down.
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.
[49]
Thermoregulation
Main articles: Physiology of dinosaurs
''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 Bakker and
John Ostrom in the early years of the "
Dinosaur Renaissance", beginning in the late
1960s.
[50][51] ''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.
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.
[52] 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).
[53] 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'').
[54] Ornithischian dinosaurs also showed evidence of homeothermy, while
varanid lizards from the same formation did not.
[55] Even if ''Tyrannosaurus rex'' does exhibit evidence of homothermy, it does not necessarily mean that it was endothermic. Such thermoregulation may also be explained by
gigantothermy, as in some living
sea turtles.
[56][57]
Feeding strategies
''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.
[58][59]
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.
[60] Modern carnivores such as
lions and
hyenas will often scavenge what other predators have killed, suggesting that tyrannosaurs may also have done so.
[61]
Some other evidence exists that suggests hunting behavior in ''Tyrannosaurus''. The ocular cavities of tyrannosaurs are positioned so that the eyes would point forward, giving the dinosaur
binocular vision.
[62] A scavenger might not need the advanced depth perception that
stereoscopic vision affords; in modern animals, binocular vision is found primarily in predators.
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 behavior between tyrannosaurs but whether it would be competition for food and mates or active
cannibalism is unclear.
[63] 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.
[64] 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.
[65][66] 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.
[67]
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."
[68] If it tripped and fell while running, a tumbling tyrannosaur's torso would have slammed into the ground at a deceleration of 6 g (six times the acceleration due to gravity, or about 60 m/s²).
(See also
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.
[59]
Locomotion
Scientists who think that ''Tyrannosaurus'' was able to run slowly 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 km/h or 25–45 mph).
[70]
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.
[71] It should be noted, however, that
giraffes have been known to gallop at 50 km/h (31 mph).
[72] 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.
[73] 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 stronger, if at all, 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.
[74] 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
[75] or it may have used ambush tactics to attack faster prey animals.
[70]
Most recent research on ''Tyrannosaurus'' locomotion does not 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''
[74] 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.
[70]
Research using computer models to estimate running speeds, based on data taken directly from fossils and published in August 2007, claims that ''T. rex'' had a top running speed of 8 metres per second (18 mph). An average professional footballer ('soccer' variety) would be slightly slower. A human sprinter can reach 12 m/s (27 mph).
[79]
According to Thomas R. Holtz Jr however, it is notable that in terms of any animal as massive as it was (5–7 tons), the tibia/femur and metatarsus/femur ratio of tyrannosaurs are the most gracile known of any animal in the Mesozoic or Cenozoic fossil record.
At the typical size of an adult ''Tyrannosaurus'', gracile limb proportions appear bulky. However, when compared to the hindlimbs of other similarly sized animals, like an elephant (as a modern example), a ''Triceratops'', or ''Edmontosaurus'', the legs of ''Tyrannosaurus rex'' are more slender and have relatively longer tibiae and metatarsi.
In relation to other large theropod families, tyrannosaurids had limb proportions that are more gracile. The smaller tyrannosaurids were even more gracile, and the smallest had the same limb proportions to the largest ornithomimids: in terms of measurement, the legs of ''
Alectrosaurus'' and ''
Gallimimus'' are identical (Holtz).
Additionally, tyrannosaurids had ornithomimid-like feet, which were smaller and more slender than that of other large theropod families, which would equate to more efficient locomotion as the leg was articulated while the animal was moving.
According to Holtz, with functional morphology as a guide, tyrannosaurids would be better adapted for speed than any other family of large theropod, including allosauroids, megalosauroids and neoceratosaurs. This may not mean that ''T. rex'' was capable of the more fantastic speed figures estimated for it, but that it was, for an animal for its size, optimised for speed, and in relevance to the predator/scavenger debate, faster than its prey.
[80]
New evidence based on biomechanic computer models suggests ''Tyrannosaurus'' had a poor turning circle. According to John Hutchinson, expert on biomechanics at the University of London's Royal Veterinary College in England, ''Tyrannosaurus'' would probably have taken one to two seconds to turn only 45° – an amount that humans, being vertically oriented and tail-less, can spin in just a fraction of a second.
[81]
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.
[82] 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.
[83]
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.
[42]
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.
[85]
Notable specimens
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
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 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. 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.
[86]
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 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''.
[87] 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.
[88][89]
Also in 2001, Dr. Jack Horner discovered a specimen of ''T. rex'' around 10% larger than "Sue". Dubbed ''C. rex'' (or "Celeste" after Jack's wife), this specimen is currently under study.
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%.
[90][91]
Appearances in popular culture
Since it was first described in 1905, ''Tyrannosaurus rex'', or "tyrant lizard king" 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").
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.
[92] ''T. rex'' has appeared numerous times on
television and in
films, notably ''
The Lost World'', ''
King Kong'', ''
The Land Before Time'', ''
Jurassic Park'', and ''
Night at the Museum''. 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. 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.
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References
★
Bite-force estimation for ''Tyrannosaurus rex'' from tooth-marked bones., Erickson, G. M., Van Kirk, S. D., Su, J., Levenston, M. E., Caler, W. E., and Carter, D. R., , , Nature, 1996
★
★
External links
★
The secret of ''T. rex's colossal size: a teenage growth spurt
★
''Tyrannosaurus'' in the Dino Directory
★
Sue's homepage
★
Stan's homepage
★
Tree of Life discussing Tyrannosauridae
★
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''
★
University of Tampa on bite force etc. of ''T. rex''
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Stanford University on bite force of ''T. rex''
★
How Tyrannosaurus might have had sex
★
Recent Discovery of Soft Tissue
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