Life history The identification of several specimens as juvenile
T. rex has allowed scientists to document
ontogenetic changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The
Stygivenator holotype (
LACM 28471, the "Jordan theropod"), possibly a juvenile
T. rex, is estimated to have weighed only , while the largest adults, such as
FMNH PR2081 (Sue) most likely weighed about .
Histologic analysis of
T. rex bones showed LACM 28471 had aged only 2 years when it died. Sue was initially estimated at 28 years old, an age which was at the time considered close to the maximum for the species, Similarly,
Trix (RGM 792.000) is estimated to have been at least 30 years old at time of death. 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 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 a year for the next four years. At 18 years of age, the curve plateaus again, indicating that growth slowed dramatically. For example, only separated the 28-year-old Sue from a 22-year-old Canadian specimen (
RTMP 81.12.1). A study by Hutchinson and colleagues in 2011 corroborated the previous estimation methods in general, but their estimation of peak growth rates is significantly higher; it found that the "maximum growth rates for T. rex during the exponential stage are 1790 kg/year". Further study indicates an age of 18 for this specimen. In 2016, it was finally confirmed by Mary Higby Schweitzer and Lindsay Zanno and colleagues that the soft tissue within the femur of MOR 1125 was medullary tissue. This also confirmed the identity of the specimen as a female. The discovery of
medullary bone tissue within
Tyrannosaurus may prove valuable in determining the sex of other dinosaur species in future examinations, as the chemical makeup of medullary tissue is unmistakable. Other tyrannosaurids exhibit extremely similar growth curves, although with lower growth rates corresponding to their lower adult sizes. An additional study published in 2020 by Woodward and colleagues, for the journal
Science Advances indicates that during their growth from juvenile to adult,
Tyrannosaurus was capable of slowing down its growth to counter environmental factors such as lack of food. Based on BMRP 2002.4.1 and BMRP 2006.4.4 between 13 and 15 years old housed at the Burpee Museum in Illinois then referred to as juvenile
Tyrannosaurus specimens, the authors suggested that the rate of maturation for
Tyrannosaurus was dependent on resource abundance. This study also indicates that in such changing environments,
Tyrannosaurus was particularly well-suited to an environment that shifted yearly in regards to resource abundance, hinting that other midsize predators might have had difficulty surviving in such harsh conditions and explaining the niche partitioning between juvenile and adult tyrannosaurs. The study further suggested that
Tyrannosaurus and
Nanotyrannus are synonymous, due to analysis of the growth rings in the bones of the two specimens studied. In 2026, Woodward, Myhrvold and Horner performed a comprehensive histological analysis of 17 tyrannosaur specimens, and argued that
Tyrannosaurus likely experienced a more gradual annual growth rate slope than indicated by earlier studies and evidence of a protracted subadult stage, reaching asymptotic size at around 35-40 years of age. The upper limit of the annual growth rate estimate is approximately 43-53 years. They also found that the growth trajectories of BMRP 2002.4.1 and BMRP 2006.4.4 do not fit with other
Tyrannosaurus specimens in their growth curve model. While they acknowledged the possibility of these ontogenetically immature specimens representing
Nanotyrannus as suggested by Zanno and Napoli (2025), they noted that the inconsistencies of these specimens observed in the growth curve do not necessarily bear weight on the proposal that
Nanotyrannus is a distinct taxon. 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 thus were not often fossilized. 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. Gregory S. Paul also writes that
Tyrannosaurus reproduced quickly and died young but attributes their short lifespans to the dangerous lives they lived.
Skin and possible filamentous feathering The discovery of
feathered dinosaurs led to debate regarding whether, and to what extent,
Tyrannosaurus might have been feathered. Filamentous structures, which are commonly recognized as the precursors of
feathers, have been reported in the small-bodied, basal tyrannosauroid
Dilong paradoxus from the Early Cretaceous
Yixian Formation of China in 2004. Because
integumentary impressions of larger tyrannosauroids known at that time showed evidence of
scales, the researchers who studied
Dilong speculated that insulating feathers might have been lost by larger species due to their smaller surface-to-volume ratio. A 2017 study reviewed known skin impressions of tyrannosaurids, including those of a
Tyrannosaurus specimen nicknamed "Wyrex" (HMNS 2006.1743.01, formerly known as BHI 6230) which preserves patches of mosaic scales on the tail, hip, and neck. A conference abstract published in 2016 posited that theropods such as
Tyrannosaurus had their upper teeth covered in lips, instead of bare teeth as seen in
crocodilians. This was based on the presence of
enamel, which according to the study needs to remain hydrated, an issue not faced by aquatic animals like crocodilians. However, there has been criticism where it favors the idea for lips, with the 2017 analytical study proposing that tyrannosaurids had large, flat scales on their snouts instead of lips, as modern crocodiles do. But crocodiles possess rather cracked keratinized skin, not flat scales; by observing the hummocky rugosity of tyrannosaurids, and comparing it to extant lizards, researchers have found that tyrannosaurids had squamose scales rather than a crocodillian-like skin. In 2023, Cullen and colleagues supported the idea that theropods like tyrannosaurids had lips based on anatomical patterns, such as those of the foramina on their face and jaws, more similar to those of modern
squamates such as
monitor lizards or
marine iguanas than those of modern
crocodilians like
alligators. Comparison of the teeth of
Daspletosaurus and
American alligators shows that the enamel of tyrannosaurids had no significant wear and that the teeth of modern crocodilians were eroded on the labial side and were substantially worn. This suggests that it is likely that theropod teeth were kept wet by lips. On the basis of the relationship between hydration and wear resistance, the authors argued that it is unlikely that the teeth of theropods, including tyrannosaurids, would have remained unworn when exposed for a long time, because it would have been hard to maintain hydration. The authors also performed regression analyses to demonstrate the relationship between tooth height and skull length, and found that
varanids like the
crocodile monitor had substantially greater ratios of tooth height to skull length than those of
Tyrannosaurus, indicating that the teeth of theropods were not too big to be covered by extraoral tissues when the mouth was closed. It was also thought that the 'robust' morphology correlated with a reduced
chevron on the first tail vertebra, also ostensibly to allow eggs to pass out of the
reproductive tract, as had been erroneously reported for
crocodiles. In recent years, evidence for sexual dimorphism has been weakened. A 2005 study reported that previous claims of sexual dimorphism in crocodile chevron anatomy were in error, casting doubt on the existence of similar dimorphism between
T. rex sexes. 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.
Posture ), showing upright pose Like many
bipedal dinosaurs,
T. 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. In 1915, convinced that the creature stood upright,
Henry Fairfield Osborn, former president of the American Museum of Natural History, further reinforced the notion in unveiling the first complete
T. rex skeleton arranged this way. It stood in an upright pose for 77 years, until it was dismantled in 1992. By 1970, scientists realized this pose was incorrect and could not have been maintained by a living animal, as it would have resulted in the
dislocation or weakening of several
joints, including the hips and the articulation between the head and the
spinal column. The inaccurate AMNH mount inspired similar depictions in many films and paintings (such as
Rudolph Zallinger's famous mural
The Age of Reptiles in
Yale University's
Peabody Museum of Natural History) until the 1990s, when films such as
Jurassic Park introduced a more accurate posture to the general public. Modern representations in museums, art, and film show
T. rex with its body approximately parallel to the ground with the tail extended behind the body to balance the head. To sit down,
Tyrannosaurus may have settled its weight backwards and rested its weight on a pubic boot, the wide expansion at the end of the pubis in some dinosaurs. With its weight rested on the pelvis, it may have been free to move the hindlimbs. Getting back up again might have involved some stabilization from the diminutive forelimbs. like the rest of the body.
Arms specimen) When
T. 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. This strongly suggested that
T. rex had similar forelimbs, but this
hypothesis was not confirmed until the first complete
T. rex forelimbs were identified in 1989, belonging to MOR 555 (the "Wankel rex"). The remains of Sue also include complete forelimbs. Newman (1970) suggested that the forelimbs were used to assist
Tyrannosaurus in rising from a prone position. Another possibility is that the forelimbs held struggling prey while it was killed by the tyrannosaur's enormous jaws. This hypothesis may be supported by
biomechanical analysis.
T. rex forelimb bones exhibit extremely thick
cortical bone, which has been interpreted as evidence that they were developed to withstand heavy loads. The
biceps brachii muscle of an adult
T. rex was capable of lifting by itself; other muscles such as the
brachialis would work along with the biceps to make elbow flexion even more powerful. The
M. biceps muscle of
T. rex was 3.5 times as powerful as the
human equivalent. A
T. rex forearm had a limited 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, 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. In the first detailed scientific description of
Tyrannosaurus forelimbs, paleontologists Kenneth Carpenter and Matt Smith dismissed notions that the forelimbs were useless or that
Tyrannosaurus was an obligate scavenger. The idea that the arms served as weapons when hunting prey have also been proposed by
Steven M. Stanley, who suggested that the arms were used for slashing prey, especially by using the claws to rapidly inflict long, deep gashes to its prey. This was dismissed by Padian, who argued that Stanley based his conclusion on incorrectly estimated forelimb size and range of motion.
T. rex itself was claimed to have been
endothermic ("warm-blooded"), implying a very active lifestyle. 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. In 2022, Wiemann and colleagues used a different approach—the
spectroscopy of lipoxidation signals, which are byproducts of
oxidative phosphorylation and correlate with metabolic rates—to show that various dinosaur genera including
Tyrannosaurus had endothermic metabolisms, on par with that of modern birds and higher than that of mammals. They also suggested that such a metabolism was ancestrally common to all dinosaurs. Even if
T. 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. Similar to contemporary crocodilians, openings (dorsotemporal fenestrae) in the skull roofs of
Tyrannosaurus may have aided thermoregulation.
Soft tissue (insets) were obtained 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
T. 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 be the result of people assuming preserved tissue was impossible, therefore not looking. Since the first, two more tyrannosaurs and a hadrosaur have also been found to have such tissue-like structures. The original endogenous chemistry was also found in MOR 1125 based on preservation of elements associated with bone remodeling and redeposition (sulfur, calcium, zinc), which showed that the bone cortices are similar to those of extant birds. In studies reported in
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". 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. Schweitzer has strongly criticized Kaye's claims and argues that there is no reported evidence that biofilms can produce branching, hollow tubes like those noted in her study. San Antonio, Schweitzer and colleagues published an analysis in 2011 of what parts of the collagen had been recovered, finding that it was the inner parts of the collagen coil that had been preserved, as would have been expected from a long period of protein degradation. Other research challenges the identification of soft tissue as biofilm and confirms finding "branching, vessel-like structures" from within fossilized bone.
Speed Scientists have produced a wide range of possible maximum running speeds for
Tyrannosaurus: mostly around , but as low as and as high as , though it running at this speed is very unlikely.
Tyrannosaurus was a bulky and heavy carnivore so it is unlikely to run very fast at all compared to other theropods like
Carnotaurus or
Giganotosaurus. Researchers have relied on various estimating techniques because, while there are many
tracks of large theropods walking, none showed evidence of running. A 2002 report used a mathematical model (validated by applying it to three living animals:
alligators,
chickens, and
humans; and eight more species, including emus and ostriches The third metatarsal was squeezed between the second and fourth metatarsals to form a single unit called an
arctometatarsus. This ankle feature may have helped the animal to run more efficiently. Together, these leg features allowed
Tyrannosaurus to transmit locomotory forces from the foot to the lower leg more effectively than in earlier theropods. A study published in 2021 by Pasha van Bijlert et al., calculated the
preferred walking speed of
Tyrannosaurus, reporting a speed of . While walking, animals reduce their
energy expenditure by choosing certain step rhythms at which their body parts
resonate. The same would have been true for
dinosaurs, but previous studies did not fully account for the impact the tail had on their walking speeds. According to the authors, when a dinosaur walked, its tail would slightly sway up and down with each step as a result of the
interspinous ligaments suspending the tail. Like rubber bands, these ligaments stored energy when they are stretched due to the swaying of the tail. Using a 3-D model of
Tyrannosaurus specimen
Trix, muscles and ligaments were reconstructed to simulate the tail movements. This results in a rhythmic, energy-efficient walking speed for
Tyrannosaurus similar to that seen in living animals such as humans, ostriches and giraffes. A 2017 study estimated the top running speed of
Tyrannosaurus as , speculating that
Tyrannosaurus exhausted its energy reserves long before reaching top speed, resulting in a parabola-like relationship between size and speed. Another 2017 study hypothesized that an adult
Tyrannosaurus was incapable of running due to high skeletal loads. Using a calculated weight estimate of 7 tons, the model showed that speeds above would have probably shattered the leg bones of
Tyrannosaurus. The finding may mean that running was also not possible for other giant theropod dinosaurs like
Giganotosaurus,
Mapusaurus and
Acrocanthosaurus. However, studies by Eric Snively and colleagues
, published in 2019 indicate that
Tyrannosaurus and other tyrannosaurids were more maneuverable than allosauroids and other theropods of comparable size due to low rotational inertia compared to their body mass combined with large leg muscles. As a result, it is hypothesized that
Tyrannosaurus was capable of making relatively quick turns and could likely pivot its body more quickly when close to its prey, or that while turning, the theropod could "pirouette" on a single planted foot while the alternating leg was held out in a suspended swing during a pursuit. The results of this study potentially could shed light on how agility could have contributed to the success of tyrannosaurid evolution. In 2026, Boeye and colleagues analyzed the foot biomechanics of
T. rex and determined that its foot likely functioned similarly to modern birds. This may have resulted in shorter stride lengths, higher stride frequencies, and a somewhat elevated top speed.
Possible footprints Two isolated fossilized
footprints have been tentatively assigned to
T. 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
T. rex, which would make it the first known footprint from this species. The track was made in what was once a vegetated wetland mudflat. It measures long by 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 long, shorter than the track described by Lockley and Hunt. Whether or not the track was made by
Tyrannosaurus is unclear, though
Tyrannosaurus is the only large theropod known to have existed in the Hell Creek Formation. A set of footprints in Glenrock, Wyoming dating to the
Maastrichtian stage of the Late Cretaceous and hailing from the
Lance Formation were described by Scott Persons, Phil Currie and colleagues in 2016, and are believed to belong to either a juvenile
T. rex or
Nanotyrannus lancensis. From measurements and based on the positions of the footprints, the animal was believed to be traveling at a walking speed of around 2.8 to 5 miles per hour and was estimated to have a hip height of . A follow-up paper appeared in 2017, increasing the speed estimations by 50–80%. Rare fossil footprints and trackways found in New Mexico and Wyoming that are assigned to the ichnogenus
Tyrannosauripus have been attributed to being made by
Tyrannosaurus, based on the stratigraphic age of the rocks they are preserved in. The first specimen, found in 1994 was described by Lockley and Hunt and consists of a single, large footprint. Another pair of ichnofossils, described in 2021, show a large tyrannosaurid rising from a prone position by rising up using its elbows in conjunction with the pads on their feet to stand. These two unique sets of fossils were found in Ludlow, Colorado and Cimarron, New Mexico. Another ichnofossil described in 2018, perhaps belonging to a juvenile
Tyrannosaurus or
Nanotyrannus was uncovered in the Lance Formation of Wyoming. The trackway itself offers a rare glimpse into the walking speed of tyrannosaurids, and the trackmaker is estimated to have been moving at a speed of , significantly faster than previously assumed for estimations of walking speed in tyrannosaurids.
Brain and senses (
Sue specimen). A study conducted by
Lawrence Witmer and Ryan Ridgely of Ohio University found that
Tyrannosaurus shared the heightened sensory abilities of other
coelurosaurs, highlighting relatively rapid and coordinated eye and head movements; an enhanced ability to sense low frequency sounds, which would allow tyrannosaurs to track prey movements from long distances; and an enhanced sense of smell. A study published by Kent Stevens concluded that
Tyrannosaurus had keen vision. By applying modified
perimetry to facial reconstructions of several dinosaurs including
Tyrannosaurus, the study found that
Tyrannosaurus had a binocular range of 55 degrees, surpassing that of modern hawks. Stevens estimated that
Tyrannosaurus had 13 times the visual acuity of a human and surpassed the visual acuity of an eagle, which is 3.6 times that of a person. Stevens estimated a limiting far point (that is, the distance at which an object can be seen as separate from the horizon) as far as away, which is greater than the that a human can see. Thomas Holtz Jr. would note that high depth perception of
Tyrannosaurus may have been due to the prey it had to hunt, noting that it had to hunt ceratopsians such as
Triceratops, ankylosaurs such as
Ankylosaurus, and hadrosaurs. He would suggest that this made precision more crucial for
Tyrannosaurus enabling it to, "get in, get that blow in and take it down." In contrast,
Acrocanthosaurus had limited depth perception because they hunted large sauropods, which were relatively rare during the time of
Tyrannosaurus.
Tyrannosaurus had very large
olfactory bulbs and
olfactory nerves relative to their brain size, the organs responsible for a heightened sense of smell. This suggests that the sense of smell was highly developed, and implies that tyrannosaurs could detect carcasses by scent alone across great distances. The sense of smell in tyrannosaurs may have been comparable to modern
vultures, which use scent to track carcasses for scavenging. Research on the olfactory bulbs has shown that
T. rex had the most highly developed sense of smell of 21 sampled non-avian dinosaur species. , Sydney Somewhat unusually among theropods,
T. rex had a very long
cochlea. The length of the cochlea is often related to hearing acuity, or at least the importance of hearing in behavior, implying that hearing was a particularly important sense to tyrannosaurs. Specifically, data suggests that
T. rex heard best in the low-frequency range, and that low-frequency sounds were an important part of tyrannosaur behavior. However, a more recent study reviewing the evolution of the trigeminal canals among sauropsids notes that a much denser network of neurovascular canals in the snout and lower jaw is more commonly encountered in aquatic or semiaquatic taxa (e.g.,
Spinosaurus,
Halszkaraptor,
Plesiosaurus), and taxa that developed a rhamphotheca (e.g.,
Caenagnathasia), while the network of canals in
Tyrannosaurus appears simpler, though still more derived than in most ornithischians, and overall terrestrial taxa such as tyrannosaurids and
Neovenator may have had average facial sensitivity for non-edentulous terrestrial theropods, although further research is needed. The neurovascular canals in
Tyrannosaurus may instead have supported soft tissue structures for thermoregulation or social signaling, the latter of which could be confirmed by the fact that the neurovascular network of canals may have changed during ontogeny. A study by Grant R. Hurlburt, Ryan C. Ridgely and Lawrence Witmer obtained estimates for
Encephalization Quotients (EQs), based on reptiles and birds, as well as estimates for the ratio of cerebrum to brain mass. The study concluded that
Tyrannosaurus had the relatively largest brain of all adult non-avian dinosaurs with the exception of certain small maniraptoriforms (
Bambiraptor,
Troodon and
Ornithomimus). The study found that
Tyrannosaurus's relative brain size was still within the range of modern reptiles, being at most 2
standard deviations above the mean of non-avian reptile EQs. The estimates for the ratio of cerebrum mass to brain mass would range from 47.5 to 49.53 percent. According to the study, this is more than the lowest estimates for extant birds (44.6 percent), but still close to the typical ratios of the smallest sexually mature alligators which range from 45.9–47.9 percent. Other studies, such as those by Steve Brusatte, indicate the encephalization quotient of
Tyrannosaurus was similar in range (2.0–2.4) to a
chimpanzee (2.2–2.5), though this may be debatable as reptilian and mammalian encephalization quotients are not equivalent.
Social behavior ''),
Natural History Museum of Los Angeles County Philip J. Currie suggested that Tyrannosaurus may have been
pack hunters, comparing
T. rex to related species
Tarbosaurus bataar and
Albertosaurus sarcophagus, citing fossil evidence that may indicate
gregarious (describing animals that travel in herds or packs) behavior. A find in
South Dakota where three
T. rex skeletons were in close proximity may suggest the formation of a pack. Cooperative pack hunting may have been an effective strategy for subduing prey with advanced
anti-predator adaptations which pose potential lethality such as
Triceratops and
Ankylosaurus. The Currie theory for pack hunting by
T. rex is based mainly by analogy to a different species,
Tarbosaurus bataar. Evidence of gregariousness in
T. bataar itself has not been peer-reviewed, and to Currie's own admission, can only be interpreted with reference to evidence in other closely related species. According to Currie gregariousness in
Albertosaurus sarcophagus is supported by the discovery of 26 individuals with varied ages in the Dry Island bonebed. He ruled out the possibility of a predator trap due to the similar preservation state of individuals and the near absence of herbivores. Additional support of tyrannosaurid gregariousness can be found in fossilized
trackways from the Upper Cretaceous
Wapiti Formation of northeastern
British Columbia, Canada, left by three tyrannosaurids traveling in the same direction. According to scientists assessing the Dino Gangs program, the evidence for pack hunting in
Tarbosaurus and
Albertosaurus is weak and based on group skeletal remains for which alternate explanations may apply (such as drought or a flood forcing dinosaurs to die together in one place). Pathologies of
Tyrannosaurus specimens have been suggested as evidence of conspecific attack, including "Wyrex" with a hole penetrating its jugual and severe trauma on its tail that shows signs of
bone remodeling (not regrowth).
Diet and feeding behavior Most paleontologists accept that
Tyrannosaurus was both an active
predator and a
scavenger like most large
carnivores. By far the largest carnivore in its environment,
T. rex was most likely an
apex predator, preying upon
hadrosaurs, armored herbivores like
ceratopsians and
ankylosaurs, and possibly
sauropods (such as
Alamosaurus). Enamel δ44/42Ca values also suggest the possibility that
T. rex occasionally fed on carcasses of marine reptiles and fish washed up on the shores of the Western Interior Seaway. A study in 2012 by Karl Bates and Peter Falkingham found that
Tyrannosaurus had the most powerful bite of any terrestrial animal that has ever lived, finding an adult
Tyrannosaurus could have exerted 35,000 to 57,000
N (7,868 to 12,814
lbf) of force in the back teeth. Even higher estimates were made by Mason B. Meers in 2003. A debate exists, however, about whether
Tyrannosaurus was primarily a
predator or a pure
scavenger. The debate originated in a 1917 study by Lambe which argued that large theropods were pure scavengers because
Gorgosaurus teeth showed hardly any wear. This argument disregarded the fact that 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. Paleontologist
Jack Horner has been a major proponent of the view that
Tyrannosaurus was not a predator at all but instead was an obligate scavenger. He has put forward arguments in the popular literature to support the pure scavenger hypothesis: '' at the
Los Angeles Natural History Museum • 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. Other paleontologists such as
Thomas Holtz Jr. argued that there are plenty of modern-day predators that do not use their forelimbs to hunt such as
wolves,
hyenas, and
secretary birds as well as other extinct animals thought to be predators that would not have used their forelimbs such as
phorusrhacids. • 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. • Since at least some of
Tyrannosauruss potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger. Despite the consensus that the tail bites were caused by
Tyrannosaurus, there has been some evidence to show that they might have been created by other factors. For example, a 2014 study suggested that the tail injuries might have been due to
Edmontosaurus individuals stepping on each other, while another study in 2020 backs up the hypothesis that biomechanical stress is the cause for the tail injuries. 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. Since the
Triceratops wounds healed, it is most likely that the
Triceratops survived the encounter and managed to overcome the
Tyrannosaurus. In a battle against a bull
Triceratops, the
Triceratops would likely defend itself by inflicting fatal wounds to the
Tyrannosaurus using its sharp horns. Studies of
Sue found a broken and healed
fibula and tail vertebrae, scarred facial bones and a tooth from another
Tyrannosaurus embedded in a neck vertebra, providing evidence for aggressive behavior. Studies on hadrosaur vertebrae from the Hell Creek Formation that were punctured by the teeth of what appears to be a late-stage juvenile
Tyrannosaurus indicate that despite lacking the bone-crushing adaptations of the adults, young individuals were still capable of using the same bone-puncturing feeding technique as their adult counterparts. In 1992,
William Abler suggested that
Tyrannosaurus may have had infectious
saliva used to kill its prey. Abler observed that the (tiny protuberances) on the cutting edges of the teeth are closely spaced, enclosing little chambers, which he argued trapped pieces of carcass with bacteria, giving
Tyrannosaurus a deadly, infectious bite, as the
Komodo dragon was mistakenly thought to have. Jack Horner and Don Lessem, in a 1993 popular book, questioned Abler's hypothesis, arguing that
Tyrannosauruss tooth serrations as more like cubes in shape than the serrations on a Komodo monitor's teeth, which are rounded.
Tyrannosaurus probably primarily processed carcasses with lateral shakes of the head, like crocodilians. The head was not as maneuverable as the skulls of
allosauroids, due to flat joints of the neck vertebrae. Evidence also strongly suggests that tyrannosaurs were at least occasionally cannibalistic.
Tyrannosaurus itself has strong evidence pointing towards it having been cannibalistic in at least a scavenging capacity based on tooth marks on the foot bones, humerus, and metatarsals of one specimen.
Parenting While there is no direct evidence of
Tyrannosaurus raising their young (the rarity of juvenile and nest Tyrannosaur fossils has left researchers guessing), it has been suggested by some that like its closest living relatives, modern archosaurs (birds and crocodiles)
Tyrannosaurus may have protected and fed its young. Crocodilians and birds are often suggested by some paleontologists to be modern analogues for dinosaur parenting. Direct evidence of parental behavior exists in other dinosaurs such as
Maiasaura peeblesorum, the first dinosaur to have been discovered to raise its young, as well as more closely related
Oviraptorids, the latter suggesting parental behavior in theropods.
Pathology In 2001, Bruce Rothschild and others published a study examining evidence for
stress fractures and
tendon avulsions in
theropod dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by regular behavior than other types of injuries. Of the 81
Tyrannosaurus foot bones examined in the study, one was found to have a stress fracture, while none of the 10 hand bones were found to have stress fractures. The researchers found tendon avulsions only among
Tyrannosaurus and
Allosaurus. An avulsion injury left a divot on the humerus of Sue the
T. rex, apparently located at the origin of the
deltoid or
teres major muscles. The presence of avulsion injuries being limited to the forelimb and shoulder in both
Tyrannosaurus and
Allosaurus suggests that theropods may have had a musculature more complex than and functionally different from those of birds. The researchers concluded that Sue's tendon avulsion was probably obtained from struggling prey. The presence of stress fractures and tendon avulsions, in general, provides evidence for a "very active" predation-based diet rather than obligate scavenging. A 2009 study showed that smooth-edged holes in the skulls of several specimens might have been caused by
Trichomonas-like parasites that commonly infect
birds. According to the study, seriously infected individuals, including "Sue" and MOR 980 ("Peck's Rex"), might therefore have died from starvation after feeding became increasingly difficult. Previously, these holes had been explained by the bacterious bone infection
Actinomycosis or by intraspecific attacks. A subsequent study found that while trichomoniasis has many attributes of the model proposed (osteolytic, intra oral) several features make the assumption that it was the cause of death less supportable by evidence. For example, the observed sharp margins with little reactive bone shown by the radiographs of
Trichomonas-infected birds are dissimilar to the reactive bone seen in the affected
T. rex specimens. Also, trichomoniasis can be very rapidly fatal in birds (14 days or less) albeit in its milder form, and this suggests that if a
Trichomonas-like protozoan is the culprit, trichomoniasis was less acute in its non-avian dinosaur form during the Late Cretaceous. Finally, the relative size of this type of lesions is much larger in small bird throats, and may not have been enough to choke a
T. rex. A more recent study examining the pathologies concluded that the osseous alteration observed most closely resembles those around healing human cranial trepanations and healing fractures in the Triassic reptile
Stagonolepis, in the absence of infection. The possible cause may instead have been intraspecific combat. One study of
Tyrannosaurus specimens with tooth marks in the bones attributable to the same genus was presented as evidence of
cannibalism. Other
tyrannosaurids may also have practiced cannibalism. ==Paleoecology==