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| Cast of a specimen nicknamed "Stan" (specimen BHI 3033), at Manchester Museum | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Dinosauria |
| Order: | Saurischia |
| Suborder: | Theropoda |
| (unranked): | Coelurosauria |
| Superfamily: | †Tyrannosauroidea |
| Family: | †Tyrannosauridae |
| Subfamily: | †Tyrannosaurinae |
| Genus: | †Tyrannosaurus |
| Osborn, 1905 | |
| Species | |
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Tyrannosaurus meaning 'tyrant
lizard') from the Greek words τυράννος (tyrannos, meaning "tyrant") and
σαύρος' (sauros, meaning "lizard"), is a genus of theropod dinosaur. The
species Tyrannosaurus rex ('rex' meaning 'king' in Latin), commonly
abbreviated to T. rex, is a fixture in popular culture. It lived
throughout what is now western North America, with a much wider range
than other tyrannosaurids. Fossils are found in a variety of rock
formations dating to the last two million years of the Cretaceous
Period, 67 to 65.5 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 clawed digits. Although other
theropods rivaled or exceeded Tyrannosaurus rex in size, it was the
largest known tyrannosaurid and one of the largest known land predators,
measuring up to 12.8 m (42 ft) in length, up to 4 metres (13 ft) tall
at the hips, and up to 6.8 metric tons (7.5 short tons) in weight. By
far the largest carnivore in its environment, Tyrannosaurus rex may have
been an apex predator, preying upon hadrosaurs and ceratopsians,
although some experts have suggested it was primarily a scavenger. The
debate over Tyrannosaurus as apex predator or scavenger is among the
longest running debates in paleontology.
More
than 30 specimens of Tyrannosaurus rex have been identified, some of
which are nearly complete skeletons. Soft tissue and proteins have been
reported in at least one of these specimens. The abundance of fossil
material has allowed significant research into many aspects of its
biology, including life history and biomechanics. The feeding habits,
physiology and potential speed of Tyrannosaurus rex are a few subjects
of debate. Its taxonomy is also controversial, 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 Description,
Size of various specimens compared with a human
Size (in green) compared with selected giant theropods
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 (13.1 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 some other
Cretaceous carnivores, such as Spinosaurus and Giganotosaurus.
The
neck of Tyrannosaurus rex formed a natural S-shaped curve like that of
other theropods, but was short and muscular to support the massive head.
The forelimbs had only two clawed fingers, along with an additional
small metacarpal representing the remnant of a third digit. In contrast
the hind limbs were among the longest in proportion to body size of any
theropod. The tail was heavy and long, sometimes containing over forty
vertebrae, in order to balance the massive head and torso. To compensate
for the immense bulk of the animal, many bones throughout the skeleton
were hollow, reducing its weight without significant loss of strength,.
Tyrannosaurus Restoration,
The
largest known Tyrannosaurus 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 Tyrannosaurus rex displayed marked heterodonty (differences in
shape). The premaxillary teeth at the front of the upper jaw were
closely packed, D-shaped in cross-section, had reinforcing ridges on the
rear surface, were incisiform (their tips were chisel-like blades) and
curved backwards. The D-shaped cross-section, reinforcing ridges and
backwards curve reduced the risk that the teeth would snap when
Tyrannosaurus bit and pulled. The remaining teeth were robust, like
"lethal bananas" rather than daggers; more widely spaced and also had
reinforcing ridges. Those in the upper jaw were larger than those in all
but the rear of the lower jaw. The largest found so far is estimated to
have been 30 centimetres (12 in) long including the root when the
animal was alive, making it the largest tooth of any carnivorous
dinosaur.
Tyrannosaurus Classification
Profile view of a skull (AMNH 5027)
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.
Reconstructed head and neck in the Naturhistorisches Museum in Vienna
Other
tyrannosaurid fossils found in the same formations as Tyrannosaurus 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 Tyrannosaurus 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 Tyrannosaurus 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,.
Tyrannosaurus Manospondylus,
Skull
of the type specimen (CM 9380) at the Carnegie Museum of Natural
History. This was heavily and inaccurately restored with plaster using
Allosaurus as a model, and has since been disassembled.
The
first named 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. Cope believed that they belonged to an
"agathaumid" (ceratopsid) dinosaur, and named them Manospondylus gigas,
meaning "giant porous vertebra" in reverence to the numerous openings
for blood vessels he found in the bone. The M. gigas remains were later
identified as those of a theropod rather than a ceratopsid, and H.F.
Osborn recognized the similarity between M. gigas and Tyrannosaurus rex
as early as 1917. however, due to the fragmentary nature of the
Manospondylus vertebrae, Osborn did not synonymize the two genera.
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 Tyrannosaurus 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 is ever formally published on,
which it has not yet been. Manospondylus gigas could then be deemed a
nomen oblitum ("forgotten name").,.
Tyrannosaurus Paleobiology,
Tyrannosaurus Life history,
A
graph showing the hypothesized growth curve, body mass versus age
(drawn in black, with other tyrannosaurids for comparison). 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 30 kg (66 lb), while the largest,
such as FMNH PR2081 ("Sue") most likely weighed over 5,400 kg (12,000
lb). Histologic analysis of Tyrannosaurus 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 Tyrannosaurus rex growth curve is
S-shaped, with juveniles remaining under 1,800 kg (4,000 lb) until
approximately 14 years of age, when body size began to increase
dramatically. During this rapid growth phase, a young Tyrannosaurus 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
Tyrannosaurus 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 Tyrannosaurus rex specimens appear to have died
within six years of reaching sexual maturity, a pattern which is also
seen in other tyrannosaurs and in some large, long-lived birds and
mammals today. These species are characterized by high infant mortality
rates, followed by relatively low mortality among juveniles. Mortality
increases again following sexual maturity, partly due to the stresses of
reproduction. One study suggests that the rarity of juvenile
Tyrannosaurus rex fossils is due in part to low juvenile mortality
rates; the animals were not dying in large numbers at these ages, and so
were not often fossilized. However, this rarity may also be due to the
incompleteness of the fossil record or to the bias of fossil collectors
towards larger, more spectacular specimens.
Tyrannosaurus Sexual dimorphism
See also:Tyrannosaurus "x"
Skeleton casts mounted in a mating position, Jurassic Museum of Asturias.
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 Tyrannosaurus 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 Tyrannosaurus 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 Tyrannosaurus 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 a 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.
Tyrannosaurus Posture
Outdated reconstruction (by Charles R. Knight), showing 'tripod' pose
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
Tyrannosaurus 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 Tyrannosaurus rex
with its body approximately parallel to the ground and tail extended
behind the body to balance the head,.
Arms of Tyrannosaurus ,
Closeup of forelimb
When
Tyrannosaurus rex was first discovered, the humerus was the only
element of the forelimb known.[For the initial mounted skeleton as seen
by the public in 1915, Osborn substituted longer, three-fingered
forelimbs like those of Allosaurus.However, a year earlier, Lawrence
Lambe described the short, two-fingered forelimbs of the closely related
Gorgosaurus. This strongly suggested that Tyrannosaurus rex had similar
forelimbs, but this hypothesis was not confirmed until the first
complete Tyrannosaurus rex forelimbs were identified in 1989, belonging
to MOR 555 (the "Wankel rex").The remains of "Sue" also include complete
forelimbs Tyrannosaurus rex arms are very small relative to overall
body size, measuring only 1 metre (3.3 ft) long. 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.
Diagram illustrating arm anatomy
Tyrannosaurus
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
Tyrannosaurus 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 evolved to
hold fast despite the stresses of a struggling prey animal.
Soft tissue
In
the March 2005 issue of Science, Mary Higby Schweitzer of North
Carolina State University and colleagues announced the recovery of soft
tissue from the marrow cavity of a fossilized leg bone, from a
Tyrannosaurus rex. 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 Tyrannosaurus 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 Tyrannosaurus
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. However, Schweitzer has strongly criticised Hayes' claims and
maintains that she really did find blood cells, and argues that there’s
no reported evidence that biofilms can produce branching, hollow tubes
like those noted in her study,.
Tyrannosaurus Skin and feathers,
Feathered dinosaurs,
Restoration of a young Tyrannosaurus, depicted with filamentous 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, skin impressions from
large tyrannosaurid specimens show mosaic scales.While it is possible
that protofeathers existed on parts of the body which have not been
preserved, a lack of insulatory body covering is consistent with modern
multi-ton mammals such as elephants, hippopotamus, and most species of
rhinoceros. 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 Thermoregulation,
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 T. Bakker and John Ostrom in
the early years of the "Dinosaur Renaissance", beginning in the late
1960s. Tyrannosaurus rex itself was claimed to have been endothermic
("warm-blooded"), implying a very active lifestyle. Since then, several
paleontologists have sought to determine the ability of Tyrannosaurus to
regulate its body temperature. Histological evidence of high growth
rates in young Tyrannosaurus rex, comparable to those of mammals and
birds, may support the hypothesis of a high metabolism. Growth curves
indicate that, as in mammals and birds, Tyrannosaurus rex growth was
limited mostly to immature animals, rather than the indeterminate growth
seen in most other vertebrates.
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 Tyrannosaurus 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,.
Tyrannosaurus Footprints,
Probable footprint from New Mexico
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,.
Tyrannosaurus Locomotion,
Replica
of a sequence of theropod footprints attributed to Megalosaurus at
OUMNH. No such sequence has yet been reported for tyrannosaurs, making
gait and speed estimates difficult.
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 (40 km/h; 25 mph), but a few as low as 5–11 metres
per second (18–40 km/h; 11–25 mph), and a few as high as 20 metres per
second (72 km/h; 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 4.5 metric tons (5.0 short 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.
Femur (thigh bone)Tibia (shin bone)Metatarsals (foot bones)DewclawPhalanges (toe bones)
Skeletal anatomy of a T. rex right leg
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 (40 km/h; 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 Tyrannosaurus weighing 5.4
metric tons (6.0 short tons) to 7.3 metric tons (8.0 short tons) 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 support speeds
faster than 40 kilometres per hour (25 mph), i.e. 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 km/h or 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
6-tonne chicken would have needed leg muscles making up almost 100% of
its body mass for running. Realistically, T. rex had the muscles to run
at about 5 meters per second (18 km/h, 11 mph)
A
study in 2007 used computer models to estimate running speeds, based on
data taken directly from fossils, and claimed that Tyrannosaurus rex
had a top running speed of 8 metres per second (29 km/h; 18 mph). An
average professional football (soccer) player would be slightly slower,
while a human sprinter can reach 12 metres per second (43 km/h; 27 mph).
Note that these computer models predict a top speed of 17.8 metres per
second (64 km/h; 40 mph) for a 3-kilogram (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,.
Tyrannosaurus Feeding strategies,
The
debate about whether Tyrannosaurus was a predator or a pure scavenger
is as old as the debate about its locomotion. Lambe (1917) described a
good skeleton of Tyrannosaurus’ close relative Gorgosaurus and concluded
that it and therefore also Tyrannosaurus was a pure scavenger, because
the Gorgosaurus’ teeth showed hardly any wear. This argument is no
longer taken seriously, because theropods replaced their teeth quite
rapidly. Ever since the first discovery of Tyrannosaurus most scientists
have speculated that it was a predator; like modern large predators it
would readily scavenge or steal another predator's kill if it had the
opportunity.
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:
Cast of the braincase at the Australian Museum, Sydney
Tyrannosaur
arms are short when compared to other known predators. Horner argues
that the arms were too short to make the necessary gripping force to
hold on to prey.
Tyrannosaurs
had large olfactory bulbs and olfactory nerves (relative to their brain
size). These suggest a highly developed sense of smell which could
sniff out carcasses over great distances, as modern vultures do.
Research on the olfactory bulbs of dinosaurs has shown that
Tyrannosaurus had the most highly developed sense of smell of 21 sampled
dinosaurs. Opponents of the pure scavenger hypothesis have used the
example of vultures in the opposite way, arguing that the scavenger
hypothesis is implausible because the only modern pure scavengers are
large gliding birds, which use their keen senses and energy-efficient
gliding to cover vast areas economically.However, researchers from
Glasgow concluded that an ecosystem as productive as the current
Serengeti would provide sufficient carrion for a large theropod
scavenger, although the theropod might have had to be cold-blooded in
order to get more calories from carrion than it spent on foraging (see
Metabolism of dinosaurs). They also suggested that modern ecosystems
like Serengeti have no large terrestrial scavengers because gliding
birds now do the job much more efficiently, while large theropods did
not face competition for the scavenger ecological niche from gliding
birds.
Tyrannosaur
teeth could crush bone, and therefore could extract as much food (bone
marrow) as possible from carcass remnants, usually the least nutritious
parts. Karen Chin and colleagues have found bone fragments in coprolites
(fossilized feces) that they attribute to tyrannosaurs, but point out
that a tyrannosaur's teeth were not well adapted to systematically
chewing bone like hyenas do to extract marrow.
Since
at least some of Tyrannosaurus's potential prey could move quickly,
evidence that it walked instead of ran could indicate that it was a
scavenger. On the other hand, recent analyses suggest that
Tyrannosaurus, while slower than large modern terrestrial predators, may
well have been fast enough to prey on large hadrosaurs and
ceratopsians.
The eye-sockets faced mainly forwards, giving it good binocular vision
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 not obvious why natural
selection would have favored this long-term trend if tyrannosaurs had
been pure scavengers, which would not have needed the advanced depth
perception that stereoscopic vision provides. In modern animals,
binocular vision is found mainly in predators.
Restoration
(based on MOR 980) with parasite infections, which might be the cause
of scars seen in the skulls of several specimens that were previously
explained by intraspecific attacks
A
skeleton of the hadrosaurid Edmontosaurus annectens has been described
from Montana with healed tyrannosaur-inflicted damage on its tail
vertebrae. The fact that the damage seems to have healed suggests that
the Edmontosaurus survived a tyrannosaur's attack on a living target,
i.e. the tyrannosaur had attempted active predation. There is also
evidence for an aggressive interaction between a Triceratops and a
Tyrannosaurus in the form of partially healed tyrannosaur tooth marks on
a Triceratops brow horn and squamosal (a bone of the neck frill); the
bitten horn is also broken, with new bone growth after the break. It is
not known what the exact nature of the interaction was, though: either
animal could have been the aggressor. 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. A 2009 study showed that holes in
the skulls of several specimens might have been caused by
Trichomonas-like parasites that commonly infect avians.
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 like most large carnivores,.
Tyrannosaurus Cannibalism,
A
study from Currie, Horner, Erickson and Longrich in 2010 has been
putted forward as conclusive evidenc of cannibalism in the genus
Tyrannosaurus. They studied some Tyrannosaurus specimens with tooth
marks in the bones, attributable to the same genus. The tooth marks were
identified in the humerus, foot bones and metatarsals, and this was
seen as evidence for opportunistic scavenging, rather than wounds caused
by intraspecific combat. In a fight, they proposed it would be
difficult to reach down to bite in the feet of a rival, making it more
likely that the bitemarks were made in a carcass. As the bitemarks were
made in body parts with relatively scantly amounts of flesh, it is
suggested that the Tyrannosaurus was feeding on a cadaver in which the
more fleshy parts already had been eaten up. They were also open to the
possibility that other tyrannosaurids practiced cannibalism.
Infectious saliva
A
partial Tyrannosaurus rex tooth; the tiny serrations (on the top right
part of the tooth in this photo) may have been the key to T. rex's
infectious saliva.
Tyrannosaurus
may have had infectious saliva used to kill its prey. This theory was
first proposed by William Abler. Abler examined the teeth of
tyrannosaurids between each tooth serration; the serrations may have
held pieces of carcass with bacteria, giving Tyrannosaurus a deadly,
infectious bite much like the Komodo Dragon. However, Jack Horner
regards Tyrannosaurus tooth serrations as more like cubes in shape than
the serrations on a Komodo monitor's teeth, which are rounded.
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 τυράννος (tyrannos, meaning "tyrant") and σαύρος (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
Skeletal restoration by William D. Matthew from 1905, the first reconstruction of this dinosaur ever published
Teeth
from what is now documented as a Tyrannosaurus 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 Tyrannosaurus rex. Vertebral fragments found by E. D.
Cope in western South Dakota in 1892 and named as Manospondylus gigas
have also been recognized as belonging to Tyrannosaurus rex.
Scale model of the never-completed exhibit planned for the American Museum of Natural History by H.F. Osborn
Barnum
Brown, assistant curator of the American Museum of Natural History,
found the first partial skeleton of Tyrannosaurus 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. In 1906, Osborn recognized the two as synonyms, and acted
as first revisor by selecting Tyrannosaurus as the valid name.The
original Dynamosaurus material resides in the collections of the Natural
History Museum, 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.
Notable specimens
Main article: Specimens of Tyrannosaurus
"Sue" specimen, Field Museum of Natural History, Chicago
Sue
Hendrickson, amateur paleontologist, discovered the most complete
(approximately 85%) 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. The
fossil collection was purchased by the Field Museum of Natural History
at auction for USD 7.6 million, making it the most expensive dinosaur
skeleton to date. From 1998 to 1999 Field Museum of Natural History
preparators spent over 25,000 man-hours taking the rock off each of the
bones. The bones were then shipped off to New Jersey where the mount was
made. The finished mount was then taken apart, and along with the
bones, shipped back to Chicago for the final assembly. The mounted
skeleton opened to the public on May 17, 2000 in the great hall (Stanley
Field Hall) 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. Early speculation that Sue may have died from a bite to the back
of the head was not confirmed. Though subsequent study showed many
pathologies in the skeleton, no bite marks were found. Damage to the
back of the skull may have been caused by post-mortem trampling. Recent
speculation indicates that "Sue" may have died of starvation after
contracting a parasitic infection from eating diseased meat; the
resulting infection would have caused inflammation in the throat,
ultimately leading "Sue" to starve because she could no longer swallow
food. This hypothesis is substantiated by smooth-edged holes in her
skull which are similar to those caused in modern-day birds that
contract the same parasite.
Samson, a Tyrannosaurus rex specimen that was put up for auction on eBay in 2000 with an asking price of over USD 8 million,.
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 man-hours of digging and
preparing, a 65% complete skeleton emerged. Stan is currently on display
in the Black Hills Institute of Geological Research 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.
"Jane" specimen, Cleveland Museum of Natural History, Cleveland, Ohio
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 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%.
Appearances in popular culture
Since
it was first described in 1905, Tyrannosaurus rex has become the most
widely recognized dinosaur species in popular culture. It is the only
dinosaur that is commonly known to the general public by its full
scientific name (binomial name) (Tyrannosaurus rex), and the scientific
abbreviation T. rex has also come into wide usage. Robert T. Bakker
notes this in The Dinosaur Heresies and explains that a name like
"Tyrannosaurus rex is just irresistible to the tongue."
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