Tyrannosaurus (pronounced /tɨˌrænəˈsɔːrəs/ or /taɪˌrænoʊˈsɔːrəs/, meaning 'tyrant lizard') is a genus of theropod dinosaur from North America. The famous species Tyrannosaurus rex ('rex' meaning 'king' in Latin), commonly abbreviated to T. rex (or incorrectly T-Rex), is a fixture in popular culture around the world, and is extensively used in scientific television and movies, such as documentaries and Jurassic Park, and in children's series such as The Land Before Time. Tyrannosaurus lived throughout what is now western North America, with a much wider range than other tyrannosaurids. Fossils of T. rex are found in a variety of rock formations dating to the last two million years of the Cretaceous Period, approximately 68 to 66 million years ago; it was among the last non-avian dinosaurs to exist prior to the Cretaceous–Tertiary extinction event.
Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small, though unusually powerful for their size, and bore two primary digits, along with a possible third vestigial digit. Although other theropods rivaled or exceeded T. rex in size]], it was the largest known tyrannosaurid and one of the largest known land predators, measuring up to 13.2 meters (43 ft) in length, up to 4 meters (13 ft.) tall at the hips, and up to 6.8 metric tonnes (7.5 short tons) in weight. By far the largest carnivore in its environment, T. rex may have been an apex predator, preying upon hadrosaurs and ceratopsians. Although some experts have suggested it was primarily a scavenger, this has been a highly controversial theory in recent years.
More than 30 specimens of T. rex have been identified, some of which are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including life history and biomechanics. The feeding habits, physiology and potential speed of T. rex are a few subjects of debate. Its taxonomy is also controversial, with some scientists considering Tarbosaurus bataar from Asia to represent a second species of Tyrannosaurus and others maintaining Tarbosaurus as a separate genus. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus.
Description[]
All Tyrannosaurus fossils are incomplete so no one knows how many bones an adult Tyrannosaurus had. One of the biggest specimen of Tyrannosaurus was Sue discovered and named after Susan Hendrickson near Faith, South Dakota, in August 1990. Sue has since been dwarfed by a specimen discovered in 1987, named by and discovered by Stan Sacrison (who also discovered Duffy). 199 bones were recovered from Stan and are now on display at the Black Hills Institute of Geological Research. Nearly 50+ specimens have been discovered since naming, with only a quarter considered complete (half the skeletal system recovered) [1].
Size[]
Various specimens of Tyrannosaurus rex with a human for scale.
Life restoration of Tyrannosaurus rex
Tyrannosaurus rex was one of the largest land carnivores of all time; the largest complete specimen, FMNH PR2081 ("Sue"), measured 12.8 metres (42 ft) long, and was 4.0 metres (13 ft) tall at the hips.[2] Mass estimates have varied widely over the years, from more than 7.2 metric tons (7.9 short tons),[3] to less than 4.5 metric tons (5.0 short tons),[4][5] with most modern estimates ranging between 5.4 and 6.8 metric tons (6.0 and 7.5 short tons).[6][7][8][9]
Although Tyrannosaurus rex was larger than the well known Jurassic theropod Allosaurus, it was slightly smaller than Cretaceous carnivores Spinosaurus and Giganotosaurus.[10][11]
Skull[]
Profile view of a Tyrannosaurus skull (AMNH 5027).
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's 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.
Skull of T. rex type specimen located at the Carnegie Museum of Natural History.
Additionally, The T. rex's jaws averaged four feet (1.2 meters) in length and were very muscular, compensating for the animal's devastating biting strength. Analysis has shown that Tyrannosaurus was capable of opening its jaws up to approximately 63-80 degrees wide, maximum. The neck of the T. rex formed a natural S-shaped curve, similar to that of other theropods, but was relatively short, and would have been immensely robust in order to support its massive head. Tyrannosaur's often-ridiculed forelimbs were only around the size of an adult human's arms, but were anchored to powerful muscles (the T. rex's arms were capable of bench pressing 400 pounds each), and, unlike dinosaurs such as Carnotaurus and its relatives, were not vestigial and would have had some use in life, although the exact purpose for them is not entirely known. Unlike more basal theropods, Tyrannosaurus hands bore only two usable digits that were tipped with sharp claws, the third being undeveloped and was too small to have shown through the skin. In contrast to the forelimbs, the hind limbs were among the longest in proportion to body size of any theropod and incredibly muscular in order to support the animal's massive bulk. Its feet resembled those of terrestrial birds, with three longer toes that would have impacted the ground, and one vestigial hallux "dewclaw" that would have never touched the ground; each toe was tipped with massive slightly hoof-like claws.
A 2012 study by scientists Karl Bates and Peter Falkingham suggested that the bite force of Tyrannosaurus could have been the strongest of any terrestrial animal that has ever lived. The calculations suggested that adult T. rex could have generated from 35000 to 57000 newtons of force in the back teeth, or the equivalent of three times the force estimated for a great white shark, 15 times the force of an African lion, 3 1/2 times the force of an Australian saltwater crocodile and around 7 times the estimated force for Allosaurus. However, even higher estimates were made by professor Mason B. Meers of the University of Tampa in 2003. In his study, Meers estimated a possible bite force of around 183000 to 235000 newtons or 18.3 to 23.5 metric tons; a bite force equivalent to that of the largest Megalodon shark specimens.
The teeth of T. rex displayed some heterodonty (differences in shape). The teeth in the premaxilla (front upper jaw) were relatively small and closely packed, D-shaped in cross-section, possessed reinforcing ridges on the rear surface, were incisiform (their tips were chisel-like blades) and curved backwards, which all would have decreased the risk of the teeth breaking when animal bit and pulled. The remaining teeth were robust with a blunter shape compared to the dagger teeth of basal theropods, more widely spaced and also possessed reinforcing roots. The teeth in the middle of the maxilla were the largest in its jaws; the biggest Tyrannosaurus tooth discovered currently was recorded as measuring 30.5 cm (12 inches) in length, including the root, making it the largest tooth of any carnivorous dinosaur and easily one of the most immense teeth in the animal kingdom. Tyrannosaurus has a robust dentary, bearing 13 teeth. Behind the teeth, the jaw raises a considerable amount. The jaws, like many theropod dinosaurs, bear many small foramina. Some propose these mark where integumentary structures were in life, such as lips or scales.
Skeleton[]
Tyrannosaurus' vertebral column consists of 10 neck, 12 back and 5 sacral vertebrae, with the exact number of tail vertebrae being unknown; possibly varying by individual, probably having at least 40. Sue has 47 caudal vertebrae. Tyrannosaurus has the signature S-curve in the neck, but was very short, deep and muscular to support the head. The axis is exceptionally short. The rest of the neck are weak opisthocoelous, with a convex front and a concave back. Their vertebral bodies have a pleurocoel on their sides. In the torso, their bodies are robust but narrow near their waist. Their undersides are keeled, fronts concave with a deep vertical trough and large pleurocoels. Neural spines are rough-fronted with rear sides built to anchor tendons. Sacral vertebrae fuse at their bodies and spines, pneumatized, and connected to the pelvis via transverse processes and sacral ribs.
The tail was long and heavy, occasionally containing over 40 vertebrae in order to balance the large head and torso. To compensate for its immense size, many bones throughout the skeleton were hollow (similar to birds and other theropods), reducing its weight without major loss of strength. The torso was wide and deep, resembling "barrel-chest". This body would have supported most of the animal's internal organs, with aid from the gastralia (belly ribs). Since Tyrannosaurus was a saurischian dinosaur, the pubis in the hips would have pointed forward and away from the backward-facing ischium.
Right forelimb of specimen "Sue"
e. Tyrannosaurus had notoriously small arms, having short and robust humeri topped by a slender but rounded end. The ulna and radius were smaller and straighter than the humerus. The second metacarpal is longer and wider than it's first counterpart, most theropods having the opposite. Each hand has two fingers, with a small underdeveloped metacarpal that was a remnant to when the lineage had three fingers. The pelvis is massive, having an extremely long and high ilium that anchored muscles and the pubis that has a boot larger than the element's entire shaft. The rear ischium is slender and straight, obliquely pointing behind and downwards. Contrasting the arms, the hindlimbs were among the greatest in size proportioned to body size. The metatarsus is "arctometatarsalian". To help reduce weight in the body, many bones are hollowed or built in a way that strength was not lost significantly.
Pelvic girdle of specimen MOR 555
Tyrannosaurus was first known from a humerus, having the first public mount in 1915. Osborn decided to give the animal large clawed hands like Allosaurus. However, a year before, Lawrence Lambe had noticed short two-fingered arms of the closely-affiliated Gorgosaurus, giving rise to the theory that Tyrannosaurus had the same, until more complete remains from the "Wankel rex" (MOR 555), and later Sue, confirmed the theory. They were only 1 meter (3.3 feet) long, some labeling them as vestigial. In 1906, Osborn first noticed large muscle attachment points in the arms, suggesting considerable strength. He brought-forth the theory that the arms were used as an anchor during mating. Other theories include helping the animal rise from a rest position. The humerus is 15-16 inches long and the ulna is 50% of the arm's length. In the first accepted description of Tyrannosaurus, Kenneth Carpenter and Matt Smith state the forearms were useless and that Tyrannosaurus was a scavenger. According to Steven M. Stanley, they arms were used for slashing prey, using it's long curved claws to inflict deep scratches[12].
Classification[]
T. rex head reconstruction at the Oxford University Museum of Natural History.
Skull casts of different Tyrannosaurus specimens
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,[13][14] both of which have occasionally been synonymized with Tyrannosaurus.[15] 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.[16]
Below is the cladogram of Tyrannosauridae based on the phylogenetic analysis conducted by Loewen et al. in 2013.
| Tyrannosauridae |
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The anatomy of tyrannosaurs, showing the variety of skeletal and cranial morphology in the group from Brusatte et al (2010).]] The first tyrannosauroids discovered were relatively small and coated with feathers. They were not the top predators of their period, since they were dwarfed by the considerably larger allosauroids. Proceratosaurus, the earliest of this family, inhabited what is now Europe during the Jurassic period, 167 million years ago. As time progressed and the carnosaurs were driven to extinction, the tyrannosauroids took over as apex predators of their environment, evolving to be larger as they traveled west into Asia and finally North America. Yutyrannus is perhaps the most well-known of these basal tyrannosauroids, famed for being the largest confirmed feathered animal; this sparked the thought that Tyrannosaurus and its near cousins may have been possessed feathers as well, however skin impressions show that Tyrannosaurus was actually mostly, if not completely, scaly[17].
Diagram showing the differences between a generalized Tarbosaurus (A) and Tyrannosaurus rex (B) skull
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.
Nevertheless, cases have been issued that perhaps Jane and the holotype skull are in fact juveniles, but may pertain to a completely different species of tyrannosaur that just hasn't been uncovered yet in the Hell Creek, a similar case to Alioramus in the Nemegt Formation, and would therefore "Nanotyrannus" was reasserted as a valid taxon. The Nano-morphs follow a similar pattern of characteristics including a long, narrow snout, less binocular vision, blade-like teeth, long, slender hind limbs, a slimmer body plan in general compared to its potential adult counterparts, and 15 or more teeth in its lower jaw compared to the typical 12-13 found in adult T. rex.
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.
Paleobiology[]
The forelimbs might have been used to help T. rex rise from a resting pose, as seen in this cast (Bucky specimen)
When asked, paleontologists determined the taste of Tyrannosaurus meat based on fat distribution, skeletal chemistry and culinary science. Their meat may have been tough with no fat pockets associated with human flavour, bitter since carnivores taste bad and probably contained heavy metals (such as the cadmium that accumulated in Late Cretaceous soil) fatal to humans[18]. Akin to modern carnivorous animal meat.
Diagram illustrating arm anatomy
The muscular system in Tyrannosaurus was extremely strong and developed compared to other dinosaurs. The tail, legs, arms and neck were covered in thick muscle tissue to help the animal move properly in life. The large thick muscles on the neck were used to move the neck and to support the large weight produced by the skull. The thighs, calves and biceps on the arms and legs were exceptionally strong. The exact use for the miniature arms remains unknown, but it is thought that Tyrannosaurus either used them as anchors whilst mating, an aid to stand up, or for toppling and grabbing prey while the animal delivered the killing bite. Some paleontologists suggest the dinosaur held onto struggling prey with it's arms while it bit down, a theory that may be supported by biomechanical analysis. Tyrannosaurus forelimbs bear extremely thick cortical bones, which some think helped withstand large force. The biceps brachii was built to withstand 199 kilograms (439 pound) of weight, working with the brachialis in the elbow, being more powerful. The M. biceps was 3.5 times more powerful than in humans. However, the elbow and shoulder was limited in movement: only allowing 40-45°, a mere amount of movement compared to Deinonychus and humans (88-130° and 360° for the shoulder and 165° at the elbow, respectively). This entire system was built to quickly grip prey[12].
Life history[]
Illustration of a juvenile Tyrannosaurus rex
The identification of several specimens as juvenile Tyrannosaurus rex has allowed scientists to document ontogenetic changes in the species, estimate the lifespan, and determine how quickly the animals would have grown. The smallest known individual (LACM 28471, the "Jordan theropod") is estimated to have weighed only 29.9 kg (66 lb), while the largest, such as FMNH PR2081 ("Sue") most likely weighed over 5400 kg (6 short tons). Histologic analysis of T. rex bones showed LACM 28471 had aged only 2 years when it died, while "Sue" was 28 years old, an age which may have been close to the maximum for the species.[9]
The same method has also allowed other specimens to be studies, developing growth curves when their ages are plotted with their mass. They have an S-shaped curve, juveniles remaining under 1800 kilograms (4000 pounds) under year 14, where their size skyrockets. This phase is marked by an increase of 600 kilograms (1300 pounds) every year for 4 years, where the curve finally levels. This indicates a dramatic slow. For example, Sue and RTMP 81.12.1 (22 years old) are separated by 600 kilograms (1300 pounds). One 2004 study on bone histology find a growth slow at 16.
Hutchinson et al. (2011) confirm this, but received higher growth peaks, finding the amount of mass they could have gained per year during those four years was 1970 kilograms. These are higher than most estimations, but lower the difference between the expected growth and actual growth. The abrupt difference at the end of the spurt may indicate maturity has been reached, which has been supported by the medullary tissue (only present in ovulating birds) in MOR 1125 ("B-Rex"). This has proven the individual was female, and this method may be valuable to determining the sex of other species, as medullary tissue has a distinct chemical makeup. Other tyrannosaurs have similar curves, but are lower to accommodate their smaller size.
Woodward et al. (2020) in Science Advances find that Tyrannosaurus was capable of lowing it's growth rates to accommodate environmental factor during growth between the juvenile and adult stage. They focused on two individuals between 13 and 15 from the Burpee Museum, finding their maturation is based on resources. Additionally, Tyrannosaurus was adapted to an environment whose resources shifted yearly. This proposes the idea that midsize carnivores had difficulty surviving, which explains the niche partition between juvenile and adult Tyrannosaurus. The study also indicates that it and Nanotyrannus are synonyms, based on growth rings of the specimens studied,
Over half of Tyrannosaurus specimens appear to have passes 6 years before sexual maturity, which is observed in other tyrannosaurs and some long-living birds and mammals. These species have high infant mortality rates and low juvenile mortality rates. Then, mortality increases after sexual maturity, likely due to reproduction stresses. A study proposes that the lack of juvenile specimens is due to a low mortality rate (they were not dying in bulk, thus, fossil specimens are rarer). This may also be because of the fossil record's incomplete nature and the bias researchers have to larger specimens, Thomas R. Holtz Jr. (2013) in a lecture suggested Tyrannosaurus lived fast and died young. This is because they reproduced quickly, compared to mammals who take a longer time. Gregory S. Paul says the same, that this also attributes to how dangerous their lives would have been[12].
Tyrannosaurid life history graph.
Some argue Nanotyrannus is distinct, due to longer limb proportions, dentary groove morphology and several other features. Brusatte, Carr, Williamson, Holtz jr., Hone and Williams argue that the groove seen in Nanotyrannus is not distinct, as it would have shallowed as the individual developed. They object the claim that Nanotyrannus (if distinct) could be closer related to albertosaurines that possessed the groove rather than Tyrannosaurus, and that that specimen could not be attributed to Tyrannosaurus. They proved that the feature is seen in the genus Tyrannosaurus, and was a widespread ontogenetic feature [19]. In 2020, a paper was published on Nanotyrannus, showing it was likely a synonym of Tyrannosaurus [20].
In 2021, a paper by Charles Marshall et al. set to find the survival rates of Tyrannosaurus infants reaching adulthood, a process which had him attempt to find the approximate number of individuals who could have existed on earth. At the end of the study, it was revealed 2.5 billion individual adult Tyrannosaurus may have existed in total, meaning the species was one of the last "evolutionary supernovas" before the K-PG impactor. Tyrannosaurus assumed the role of a morphospecies, meaning the animal took many different niches until adulthood, where it reached apex predator. They compared Tyrannosaurus to many extant predators like lions and komodo dragons, comparing blood temperature, range, population density and growth curves to determine a likely number. They found that among the 2.5 billion, only about 20,000 individuals could be supported at one time. They estimate that for every one fossilized individual, 80,000 others did not preserve, and every 1 in 16,000 for the famous Hell Creek Formation. In the paper, they state the models are only a "ballpark estimate" and not data, but such information could be further revised in the future [21][22][23][24]. Juvenile tyrannosaurus are hypothesized to have driven contemporaneous medium-sized theropods to extinction.[25] A 2023 study used this estimate to suggest that the rate of preservation among individuals cannot determine a full population size, but note that it may be applied to other taxa variously because it only requires a growth trajectory and estimates of up to three traits that are seen in this trajectory[26].
Posture[]
  Outdated reconstruction (by Charles R. Knight), showing 'tripod' pose. |
  Replica at Senckenberg Museum, showing modern view of posture. |
Like many bipedal dinosaurs, Tyrannosaurus rex was historically depicted as a 'living tripod', with the body at 45 degrees or less from the vertical and the tail dragging along the ground, similar to a kangaroo. This concept dates from Joseph Leidy's 1865 reconstruction of Hadrosaurus, the first to depict a dinosaur in a bipedal posture.[27] Henry Fairfield Osborn, former president of the American Museum of Natural History (AMNH) in New York City, who believed the creature stood upright, further reinforced the notion after unveiling the first complete T. rex skeleton in 1915. It stood in this upright pose for nearly a century, until it was dismantled in 1992.[28] 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.[29] The mentioned mount inspired many media interpretations until the early 1990s, where mainstream film introduced the active bipedal dinosaur[12].
Distribution[]
Over 30 specimens of Tyrannosaurus have been discovered, most found in North America, and several others found in Asia. The most well known rock formation Tyrannosaurus specimens are known from is the Hell Creek Formation, located in Montana and dating to to the Late Cretaceous. Here is a list of all known locations Tyrannosaurus remains have been found in Montana, Texas, Utah, Wyoming, Alberta, Saskatchewan and New Mexico[12].
Paleopathology[]
Trichomonosis as seen in Sue.
The world-renowned specimen, Sue, is one of the most consistent tyrannosaurs to show disease and injury. While studying the specimen, scientists noticed many injuries. Sue had began to develop arthritis in the caudal vertebrae located in the tail. This disease was likely caused by age. Sue was about 28 years old when they died, which is why the joints in its tail began to swell, causing arthritis. Other pathologies recorded in Sue's skeleton include healed fractures on the ribs, broken legs which had became infected and healed, gashes in the vertebrae caused by other tyrannosaurids and unnatural holes in the mandible. Scientists speculate that the strange holes in the lower jaw would have made normal feeding techniques extremely painful, and may have been the cause of death. Similar holes torn into the lower jaws of tyrannosaurids have been observed in Daspletosaurus and some modern bird species today, caused by an infectious disease named trichomonosis.
The Montana Dueling Dinos specimen was recovered from private collections in 2020. This specimen preserves a Tyrannosaurus and a Triceratops in death positions, presumably battling. The Tyrannosaurus' teeth are all broken, the skull is smashed in and a finger is broken. Several Tyrannosaurus teeth are embedded into its enemies vertebrae.
Sue the Tyrannosaurus preserves osteomyelitis, a bone infection that travels through the bloodstream and infects other tissue, then allowing the bone to be exposed to germs. This infection can be found in the left fibula and caudal vertebrae of a Tyrannosaurus specimen. Analysis shows neoplasia rates in non-avian dinosaurs as low as 3.1% and 1.8%, while infectious-disease rates in birds and dinosaurs are 32% and 53.9%. The fibula is roughly 68 centimeters long, and appear grossly deformed, with abnormal growths and strange tapered ends. A 3D model of the bones were made and the original were CT-scanned, showing many different fused elements in Sue's femur [30].
Brice Rothscield et al. (2001) published on stress fractures and tendon avulsions in theropods and how it affects their behaviour. Stress fractures are caused by repeated trauma, therefore, they are more likely t be caused by repeated behaviour than single occurrences. From 81 Tyrannosaurus bones, 1 had no fracture and none of the 10 hand bones examined had any. They found tendon avulsions only in Tyrannosaurus and Allosaurus. One avulsion injury left a divot in Sue's humerus, located at the deltoid and teres origin. Since the injury was in the forelimbs and shoulders, it was determined they (Tyrannosaurus and Allosaurus) had more complex musculature than birds, and was likely different functionally. They found the avulsion in Sue was likely from struggling prey. This suggests active predation rather than scavenging. Holes with smooth edges in the skulls of several specimens may have been caused by a parasite similar to Trichomonas gallinae. Some individuals that are seriously infected include Sue and Peck's Rex, who likely died from starvation due to the inability to eat. Previously, these were explained by the bone infection Actinomycosis and intraspecific attacks. Some specimens show tooth marks, specifically one with marks on the humerus, feet bones and metatarsals. They may indicate opportunistic scavenging , which other tyrannosaurs may have done[12].
Vocalization[]
Tyrannosaurus probably used closed mouth vocalization, a trait used in crocodiles. Tyrannosaurus may have made loud, deep bellowing sounds, which would had felt like intense vibrations. The sound would have been a nearly inaudible booming sound, which would have rumbled through the dense arid forests in Late Cretaceous Montana. Instead of exhaling to make the sound, the sound is made in birds by sucking in air while their beaks are closed. The sound releases as a deep rumbling sound, while the jaws still remain closed. Other animals would have barely been able to hear the noise, but would have been able to feel it. [31][32]
Integument and Soft Tissue[]
T. rex femur (MOR 1125) from which demineralized matrix and peptides (insets) were obtained
Since the discovery of feathers, the debate whether Tyrannosaurus had feathers, or to what extent, has been ongoing. Since the discovery of Dilong, filamentous fur-like integument was known to have been a key factor in small theropods. Because larger tyrannosauroid skin impressions showed signs of scales, authors speculated the lineage lost their coat due to surface-to-volume ratio. However, when Yutyrannus was named, a fossil of a large tyrannosaur with a full coat of feathers, many doubted the feature was related to size. In 2017, the skin impressions from Tyrannosaurus were reviewed, based on the Wyrex specimen, preserving scales from the tail, neck and hip. They concluded that, if feathers were present, were limited to the upper trunk.
A conference abstract in 2016 argues theropods' upper jaw teeth were sheathed by lips rather than the openness seen in crocodilians. If enamel were present, it were to need constant hydration, something modern crocodilians do not need to worry about. In 2017, an analytical study suggests Tyrannosaurus had large flat scales on their snouts, rather than lips. However, this idea has been criticized, and favours the presence of lips. Crocodiles have cracked keratin integument, rather than scales. By contrasting the hummocky rugosity in Tyrannosauridae with extant lizards, researchers found Tyrannosaurus had squamose scales rather than crocodilian-like skin. Based on close relatives and the weather of the Hell Creek Formation, scientists have suggested that Tyrannosaurus was scaly, possibly with sparse feather covering, because such a large body size would have overheated the animal and such a feature would be unnecessary [33][34].
In March 2005, an issue of Science by Mary Higby Schweitzer et al. announces the discovery of Tyrannosaurus material with a preserved marrow cavity. The bone had been reluctantly broken open while shipping, and the fossil itself was not fossilized normally. It was excavated from Hell Creek, given ID MOR 1125, and was hoped to test for soft tissue. In the bone lay flexible bifurcating blood vessels and fibrous elastic bone matrix, with microstructures appearing like blood cells inside the matrix and vessels, resembling those of ostriches. It is unknown how this fossilized, whether a distinct process or the material is original. Scientists are reluctant to classify this. If the material is original, surviving proteins may help determine DNA content in dinosaurs (as different genes produce different proteins). The absence of discoveries akin to this may be because it was assumed such preservation was impossible, and any material went unrecognized. Since, two more tyrannosaurs and a hadrosaur have been found. Research suggests birds are closer in relation to tyrannosaurs than any modern animal. Reported by Science in April 2007, Asara et al. found seven traces of collagen protein in purified Tyrannosaurus remains, closely matching chickens, with frogs and newts also tested. Proteins from a dinosaur, and another bone from a mastodon, changes the perception of fossils, introducing biochemistry as a new form of study. Until then, paleontologists assumed the process of fossilization replaced all tissue with minerals. Hans Larsson states this discovery is "a milestone" and it could "enter the field of molecular biology and really slingshot paleontology into the modern world"[12].
The discovery was questioned by Thomas Kaye et al. in 2008. They state the tissue was a biofilm created by bacteria to replace the now-decayed tissue. They found the "blood cells" were framboids, finding the same from fossil ammonites. The spheres were found where the detected iron would have not been associated with in life. Schweitzer counters, stating no known biofilms can create such branching narrow structures, as reported. San Antonio, Schweitzer et al. published in 2011 on the recovered collagen, finding the inner coil preserved, as expected. Other studies challenge this, finding similar structures, chalking it up to biofilm. In 2005, it was announced that the specimen "Scotty" preserves blood vessels in the rib[35].
| Species | Age | Material | Reference(s) |
|---|---|---|---|
| T. rex | ~66 million years ago | A crushed bone fragment, Hoescht stained. It is likely endogenous DNA, since there is no better alternative. | [36] |
| T. rex | ~66 million years ago | Circular nuclei, known from isolated bone cells. Likely endogenous DNA. | |
| T. bataar | ~80 million years ago | A centrally-located nucleus and nucleolus, known from isolated bone cells. Endogenous DNA, needing more material. | |
| T. rex | "Maastrichtian" | Stringy blood vessels found in the rib of "Scotty". | [37] |
Morphs[]
As more Tyrannosaurus fossils were excavated, scientists began to notice two distinct morphs. They were termed the robust and gracile morphs. In such morphs, morphological differences are observed that helps distinguish sex. The robust morph is though to have been female, with wider hips and a reduced first chevron from the tail to create a passage for eggs. This has been observed in crocodiles. Recently, differentiated sex is becoming less likely, as a 2005 paper states the crocodile trait was an error, doubting the two sexes were different. From Sue, an extremely robust specimen, a full chevron was recovered, meaning it could not be used to separate them. Specimens from Saskatchewan and New Mexico seem to indicate the morphs were of geographical variation or age-related with the robust being older, rather than sexual dimorphism. However, one Tyrannosaurus specimen, B-Rex, has been conclusively name a female. This specimen preserved tissue, including from the medullary region. This area is only present in modern birds, producing calcium to aid in eggshell development during ovulation. Additionally, medullary tissue is never found in crocodiles, but always in birds, demonstrating their close evolutionary relationship[12]. These morphs were named as T. regina (gracile) and T. imperator (robust) in 2022, but this is controversial.
Resting and Falling[]
Tyrannosaurus, in life, would have sat by balancing on the pubic boot whilst resting back, able to move it's limbs since the weight has been redirected. When getting up, it might have used it's forelimbs to stabilize (called Newman's pushup theory). If the animal fell, it could likely get up by placing the limbs under the body and using the tail to balance. Rarely, fossil trackways from New Mexico and Wyoming are assigned the ichnogenus Tyrannosauripus, trackways associated with Tyrannosaurus based on stratigraphic data. The first specimen was found in 1994 and described by Lockley and Hunt: a large footprint. Trackways from the Raton Formation show a resting prone Tyrannosaurus individual that stepped forward using it's left hindlimb while pushing down on the ground with it's arms, palms and feet in conjunction. This shows that Tyrannosaurus likely rose from a quadrupedal stance, the animal then using the hind legs to gain balance. This shows that tyrannosaurids could have gotten up from a fall or from a resting position [38]. These fossils were discovered in Ludlow, Colorado and Cimarron, New Mexico. Another ichnofossil described in 2018 from the Lance Formation belongs to a juvenile Tyrannosaurus ("Nanotyrannus"), moving at 4.5-8 kilometers/hour (2.8-5 miles/hour), a speed faster than assumed walking estimations[12].
Diet[]
Tyrannosaurus tooth marks on bones of various herbivorous dinosaurs
A Tyrannosaurus mounted next to a Triceratops at the Los Angeles Natural History Museum
Most think that Tyrannosaurus was an active predator and scavenger. It was the largest predator in it's environment, most likely an apex predator. It preyed upon hadrosaurs, ankylosaurs, ceratopsians and maybe sauropods. Karl Bates and Peter Falkingham (2012) found that Tyrannosaurus had the most powerful bite force of any terrestrial animal, exerting 35,000-57,000 Newtons (7868-12,814 pounds) nearer to the back of the mouth. Higher estimates by Mason B. Meers in 2003 were made. Tyrannosaurus could crush bone by repetitively biting and eventually consuming . Stephan Lautenschlager et al. calculates a maximum gape of ~80°, which powered it's strong bite. It is debated whether Tyrannosaurus was a predator or a pure scavenger. This was assessed by Lambe in 1917, citing the lack of wear on Gorgosaurus teeth. This may not be a valid argument, however, since tyrannosaurs regularly shed and replaced teeth. Since discovery, Tyrannosaurus was named a predator, one that would have eaten and stolen carcasses like a scavenger if presented the opportunity. Jack Horner has been a major character in the scavenger argument, stating it was an exclusive scavenger. He cites the following:
- Horner argues the short arms were too short to grip prey.
- A greater sense of smell to detect carcasses from long range.
- Tyrannosaurus could crush bone to extract marrow from it (although further study showing it could not chew bone like modern scavengers do).
- The animal was slower than previously estimated.
All of these points have been countered.
The damage to the tail vertebrae of this Edmontosaurus annectens skeleton (on display at the Denver Museum of Nature and Science) indicates that it may have been bitten by a Tyrannosaurus
Specimens from Edmontosaurus annectens show healed tyrannosaur-inflicted damage. This includes wounds in the tail vertebrae. The current consensus is that the animal survived an attempted attack from Tyrannosaurus, with some evidence pointing towards a different cause. One 2014 study places the on Edmontosaurus individuals stepping on each other, and a 2020 study on biomechanical stresses. One interaction preserves in a Triceratops, with bite marks on the brow horn and squamosal. The horn shows signs of breakage and regrowth. It is unknown which animal was the aggressor, with evidence pointing to the Triceratops overcoming a Tyrannosaurus due to healing. Triceratops would have likely defended by impaling the Tyrannosaurus with it's brow horns. In Sue, broken and healed fibula and tail vertebrae are present alongside scarred facial bones and another Tyrannosaurus tooth embedded in a neck vertebra. Studies on Hell Creek hadrosaurs show that juvenile Tyrannosaurus, although lacking the bone crushing capabilities of their adult, still inflicting puncturing wounds. Tyrannosaurus may have had infectious saliva that aided in the killing of prey, like extant varanids. This was proposed by Willian Abler in 1992, observing that the tiny protuberances in the teeth are closely spaced with small chambers between them. These may have trapped small chunks of food, giving the predator a bite that carried harmful bacteria. Horner and Don Lessem question Abler in 1993, arguing Tyrannosaurus had serrations more like cubes than the rounded ones of varanids. Tyrannosaurus processed carcasses like many theropods did, shaking the head laterally. Tyrannosaurus did not have a head that was as maneuverable as allosauroids due to flat joints at the neck vertebrae.
According to the Field Museum, the teeth of Tyrannosaurus would have carried loose chunks of flesh in life. This would have caused the mouth to have reeked. The study was conducted to be part of an attraction in Sue the Tyrannosaurus' suite in the Field Museum, were visitors can smell Sue's breath and touch it's skin. Evidence suggests tyrannosaurs, like Tyrannosaurus specifically, were cannibalistic; the latter was cannibalistic at least in scavenging, based on tooth marks on foot bones, the humerus and metatarsals in one specimen. Fossils from the Kirtland, Fruitland (Campanian) and the (Maastrichtian) Ojo Alamo Formations suggest cannibalism in multiple genera in the San Juan Basin. This evidence suggests opportunistic feeding. Currie, Horner, Erickson and Longrich (2010) suggests Tyrannosaurus cannibalism. They found Tyrannosaurus remains with tooth scrapes attributable to Tyrannosaurus from the humerus, foot and metatarsals. This has been interpreted as opportunistic scavenging rather than injury sustained from intraspecific combat. The main evidence for that is that it would difficult to bite the feet during heated combat. Since the areas exhibiting bites bore light soft tissue in life insinuates the animal was feeding from a carcass that had already been stripped of heavy soft tissue. The authors concluded it may be possible other Tyrannosauridae did the same[12].
A 2021 study on juvenile Tyrannosaurus bite force was conducted based on mechanical tests attempting to replicate fossil bite marks, using a 13-year-old specimen (BMR P2002.4.1). BMR P2002.4.1 was digitalized and sculpted in cobalt chromium alloy (dental-grade), then tested on multiple bovine long bones. Through a total of 17 trials it was determined a bite force of up to 5641.19 Newtons based on puncture marks on Edmontosaurus and other Tyrannosaurus. This falls within range of the expected force of adults, but is different than other estimates. This may shed a light on how juvenile tyrannosaurs differed in terms of niche partitioning and ontogenetic roles of Tyrannosaurus in ecosystems[39].
Thermoregulation[]
Restoration showing partial feathering
Since 2014, it has been conclusively decided if Tyrannosaurus was endothermic or ectothermic. The latter idea was the original consensus in paleontology, first challenged by Bakker and Ostrom during the late 1960's ("Dinosaur Renaissance"). Since, many want to determine the answer. Growth rates similar to mammals and birds may support the theory of a high metabolism, as growth curves similar to those groups show that growth was limited to immature animals rather than the intermediate growth in most vertebrates. Oxygen isotope ratios found in bone can be used to find the temperature it was deposited in (isotope ratios correlates with temperature). One specimen shows ratios from different areas of the body with a temperature difference no more than 4-5° Celsius (7-9° Fahrenheit), between the torso vertebrae and the lower tibia. Since this range is relatively small, Reese Barrick and William Showers claim Tyrannosaurus was homeothermic, with a metabolism between ectothermic reptiles and endothermic mammals. Others state the ratio of oxygen isotopes does not fully correlate with the animal's temperature during life, being altered as it fossilized. They defend their claim by analyzing another dinosaur from another continent and time era; Giganotosaurus. Additionally ornithischians showed homeothermy and varanids from the same formation did not. If Tyrannosaurus was homeothermic, it does not necessarily mean it displayed endothermy. Thermoregulation may be explained by gigantothermy (seen in some sea turtles). Similar to alligators, Tyrannosaurus' dorsotemporal fenestra may have aided in the thermoregulation process[12].
Speed and Agility[]
Estimates for Tyrannosaurus running speeds vary: 9 meters/second (32 kilometers/hour, 20 miles/hour), 4.5-6.8 meters/second (16-24 kilometers/hour, 10-15 miles/hour) and even 20 meters/second (72 kilometers/hour, 45 miles/hour), with the animal running at such a speed unlikely. Tyrannosaurus likely had leg muscles larger than any animal today, likely unable to sprint fast because of it's size compared to smaller dinosaurs. Paleontologists use many techniques to determine such data, with large theropod tracks discovered, but never running. A mathematical model in a 2002 report (validated by many animals including alligators, chickens, humans, emus and ostriches...) tested the necessary muscle mass in order to run over 40 kilometers/hour or 25 miles/hour. Some point to lightened build being proof, or that some modern animals achieve high speeds with slow, but long, strides. If a Tyrannosaurus were to achieve 10 kilometers/hour (25 miles/hour), about 40-86% of it's total mass would have to be leg muscle. Large muscle mass would have been needed moderately quick speeds, only being able to achieve 18 kilometers/hour (11 miles/hour), a walk/jog speed. Holtz notes that tyrannosaurids and some closely related groups have exceedingly larger distal hindlimb elements, including the shin, toes and foot compared to the femur of most theropods, with tyrannosauridae and relatives having tightly-interlocked metatarsus. In between the second and fourth metatarsals is the third metatarsal, forming the single arctometatarsus. This feature in the ankle may have helped to move efficiently, allowing the animal to transmit locomotory force to the foot more effectively than earlier theropods[12].
Only known tyrannosaurid trackway (Bellatoripes fredlundi), from the Wapiti Formation, British Columbia
In 2020, Dececchi et al. compare leg proportions, body mass and the gaits of 70+ theropods (including Tyrannosaurus and relatives) to find Tyrannosaurus was an incredibly efficient walker. They applied multiple methods to determine how much energy is required to run and walk. Along with dromaeosaurids, longer legs are better for running, but animals about 1000 kilograms (2200 pounds) in weight were unable to run faster, with longer legs then correlated to walking. This reinforces the idea that small theropods evolved longer legs for running and hunting, while larger theropods did to reduce energy and increase foraging efficiency, now freed from predation pressure as the apex predator. When compared with basal theropods, tyrannosaurids show an increase in foraging efficiency due to reserved energy from efficient hunting or scavenging. This likely results in tyrannosaurs reducing their need for hunting forays, requiring less food as a result. The research also points that tyrannosaurs were more agile than most large-bodied theropods, stalking prey for long distances, going for a burst of speed to take prey. This is similar to wolves, as at least some tyrannosaurs hunted in groups. In 2017, Tyrannosaurus' top speed was estimated as 17 miles/hour (27 kilometers/hour), speculating it would have been exhausted well before top speed. This is a relationship between size and speed. Another study in 2017 hypothesized that Tyrannosaurus was incapable of running at high speeds due to skeletal loads: at an estimated weight of 7 tons, the model's legs would shatter above 11 miles/hour (18 kilometers/hour), making running impossible for all large theropods. However, Eric Snively et al. (2019) states that Tyrannosauridae was more maneuverable than allosaurs and other large theropods due to low rotational inertia in comparison to body mass and large leg muscles. Thus, the animal could make quick turns and possibly even pivot when close to prey items or turning, spinning on a planted foot, with the other leg suspended in the air. This study may highlight how tyrannosaur agility helped the group gain an evolutionary advantage [40][41].
Recent 2021 research and publication suggests that the Tyrannosaurus was neither a fast, nor an agile theropod, in fact an average human should be easily capable of out-walking, pacing a regular Tyrannosaurus. The new simulations based on tail movement showed that T. rex wasn't even a quick walker. In fact, its preferred walking speed clocked in at just under 3 mph (5 km/h), about half the speed of earlier estimates. To put that into perspective, that's about the average walking speed for a human, according to the British Heart Foundation. An adult T. rex would have measured about 40 feet (12 meters) long, stood 12 feet (3.6 m) tall and weighed about 11,000 to 15,500 pounds (5,000 to 7,000 kilograms) on average, according to the American Museum of Natural History in New York City. The heaviest known T. rex, a hefty specimen found in Saskatchewan, Canada, and nicknamed "Scotty," weighed in at a whopping 19,555 pounds (8,870 kg), Live Science previously reported. But, how fast could such a big animal could move was unknown. Previously, researchers answered that question by looking at T. rex's mass and hip height, sometimes incorporating stride length from preserved trackways. Those estimates placed a T. rex's walking speed roughly between 4.5 and 6.7 mph (7.2 and 10.8 km/h), about as fast as an average/normal human runner [42][43]. The speed estimates found out that an adult Tyrannosaurus ideal or the most suitable walking speed was just under 3 mph (5 km/h), which was about half the speed predicted earlier.[44][45][46][47][48][49][50] Tyrannosaurus could have been a rather slow forager instead of an agile pursuit predator as it needed to conserve energy as much and often as possible.[51] Other research suggests that adults were slower with forager locamotion, while their young were more nimble[52][53].
Senses[]
The eye-sockets faced mainly forwards, giving it good binocular vision (Sue specimen).
Lawrence Witmer and Ryan Ridgely found Tyrannosaurus had heightened sensory capabilities similar to other coelurosaurians, with: quick and controlled head and eye movements, enhanced low frequency detection to track prey from a distance and enhanced smell. Kent Stevens concludes Tyrannosaurus had keen vision, applying perimetry to the face of multiple dinosaurs, Tyrannosaurus had binocular vision of a ranger of 55°, greater than a hawk. Stevens estimates Tyrannosaurus had 13x the visual acuity as the average human, surpassing the 3.6x in eagles. He also estimates the limiting far point to 6 kilometers (3.7 miles) away, far greater than the 1.6 kilometers (1 mile) in humans. Holtz Jr. notes this may have been due to what it hunted, Triceratops, Ankylosaurus and Edmontosaurus, able to track the precise social behaviours in prey. This enabled Tyrannosaurus to track prey and make blows with precision. This contrasts large predators at the time, such as Acrocanthosaurus, due to prey being scarcer. Tyrannosaurus, relative to brain size, had large olfactory bulbs and nerves, parts responsible for smell. This insinuates Tyrannosaurus had a developed sense of smell, detecting carcasses only by smell from large distance. This is compared to vultures, who do the same. Of 21 non-avian dinosaurs tested, Tyrannosaurus had the best sense of smell. Tyrannosaurus had long cochlea, related to hearing acuity and behaviour, showing tyrannosaurs found importance in hearing. Tyrannosaurus heard a low frequency range at best, and such sounds were important. Thomas Carr et al. (2017) found Tyrannosaurus and tyrannosaurids had sensitive snouts, having many small pits that filled with sensory neurons in life. This was found in Daspletosaurus. They speculate tyrannosaurs may have used their snouts to measure the temperature of their nests and to pick up eggs and children, like in modern crocodilians.
Soichiro Kawabe et al. (2021) confirmed this. They found a complex network of sensory organs in the snout of Tyrannosaurus. Nerves are the most complexly distributed of all dinosaurs. They found it was able to recognize different areas, materials and movement with great accuracy. This would have enabled it to have eaten bodies depending on the situation. Neurovascular canals branched through the anterior of the dentary. Because it may have lacked the thick integument seen in crocodilians, it was likely more sensitive; and ornithischians, when compared, did not match the level seen in Tyrannosaurus. However, the team was not able to fully study the mandible and compare enough dinosaurs to be seen as sufficient, so their findings are seen as "a reasonable estimate"[54]. Grant R. Hurlburt, Ryan C. Ridely and Lawrence Witmer created estimates for the Encephalization Quotient (EQ) of Tyrannosaurus based on birds and reptiles and an estimate for the cerebrum/brain mass ratio. Tyrannosaurus had the largest brain of any non-avian dinosaur, except for small maniraptoriforms (Bambiraptor, Troodon and Ornithomimus). It's brain size was within the ranges of modern reptiles, being, at the most, 2 deviations above the non-avian reptile mean EQs. The cerebrum/brain mass ratio would have been 47.5-49.53%, more than the 44.6% of extant birds and close to the smallest sexually mature alligators of 45.9-47.9%. Other studies, some by Steve Brusatte, indicate an EQ was 2-2.4% in range of a chimpanzee (2.2-2.5%), although this is debatable, since mammal and reptile EQs are often not equivalent[12].
A relatively recent research have found that the Tyrannosaurus had nerve sensors in the tips of its jaws that could recognize the varied parts of its prey. Researchers from Japan's Fukui Prefectural University scanned a fossil T. rex jaw From this they were able to reconstruct the blood vessels and nerves from within They found that the 'tyrant lizard kind' most likely had a very sensitive mouth It may have been able to use its mouth to help build nests and care for young.[55][56][57] Controversially, it may have had a neuron count similar to papions and possibly the ability to develop culture, but this research is disputed[58].
Intraspecific Behaviour[]
Mounted skeletons of different age groups (skeleton in lower left based on the juvenile formerly named Stygivenator), Natural History Museum of Los Angeles County
Philip J. Currie suggested Tyrannosaurus may have been a pack hunter, comparing it to close genera that have proven fossil evidence of pack behaviour. One site in South Dakota suggests the animals were close together, suggesting pack. It has been suggested that pack hunting may have been ideal to take on prey with great defenses, especially in Hell Creek. This hypothesis has been criticized due to it not being peer-reviewed, as the concept was only discussed in a broadcasted interview and in a book: "Dino Gangs". The entire idea is based on the evidence in Tarbosaurus bataar, such evidence not being peer-reviewed either. Such evidence has been cited as weak, since events, such as floods, could have swept individuals together or drought forcing animals in one spot. However, tracks from the Wapiti Formation indicate animals moving together and possibly a pack. Found by Joseph Peterson, intraspecific attack is notable in the juvenile specimen Jane. Peterson et al. found healed punctures in the upper jaw and rostrum, thought to have been from another juvenile. CT scans would further confirm this. They also found the punctures were different from ones that would result from parasites.
Recent studies of a fossil area, that shown several specimens of different life stages of Tyrannosaurus that died together, this could indicate the pack or group behaviour in Tyrannosaurus. The publication studies a group of tyrannosaur fossils that were found buried together in Rainbows and Unicorns Quarry at the Grand Staircase-Escalante National Monument. With a skull of the same species found about two miles north of the site. Alan Titus thinks that the site could be evidence that tyrannosaurs worked together as pack hunters. He says: “Now you’ve got these giant terrestrial predators behaving in a group, much more akin to a pack of wolves and a pride of lions, is staggering,”. But as he and other experts note, true pack hunting is rare among living predators. Social behavior among predators ranges from the least tolerance of another, to coordinated pack attacks and cooperation. This site is not the first example of tyrannosaurs discovered in the same place, but a thorough reconstruction of the area’s geologic history gives strong evidence that they died in a group. It is still unknown what the group was doing together[12].
The 75-million-year-old site, named Rainbows and Unicorns Quarry by Titus’ colleague for it's incredible specimens, is the first of its kind in the southern United States. However, it’s not the only evidence that tyrannosaurs gathered in groups. One bonebed in Alberta, Canada contains the fossil remains of 12-14 Albertosaurus, seemingly concentrated together during a flood. From Montana, an area about half the size of a tennis court contains the remains of ~3 Daspletosaurus. A site in South Dakota, the same area preserving Sue, contained remains of other T. rex. Fossil tracks might also provide evidence. In 2014, scientists announced that a British Columbia site preserves footprints of three tyrannosaurs walking in the same direction, with some prints taken either a short time after or the same time. Researchers argued that the site could point to social behavior, suggesting a tyrannosaur group be called a “terror”. Thomas Carr, not involved in the study, states that finding more evidence of dinosaur sociability is expected. Extinct dinosaurs belong to archosaurs, including social animals like birds, alligators, and crocodiles.[59]
Mating[]
Using the behaviours of extant archosaurs, a team of palontological consultants working on the documentary Prehistoric Planet were able to use phylogenetic bracketing to determine that Tyrannosaurus likely used appeasement/conciliation with throat display. By doing this, they would have raised their heads while releasing closed-mouth vocalizations that originated from the chest and neck. The sensitivity of their faces likely allowed for nuzzling, rubbing and/ore biting[60].
History[]
Skeletal restoration by William D. Matthew from 1905, which was the first reconstruction of Tyrannosaurus rex ever published[61]
Teeth now attributed to Tyrannosaurus were found by Arthur Lakes in 1874 near Golden, Colorado. Postcranials found by John Bell Hatcher in the early 1890s in Wyoming are also documented. These fossils were attributed to Ornithomimus grandis (now Deinodon), now attributed to Tyrannosaurus rex. Edward Drinker Cope found fragmented vertebrae in 1892, which he attributed the two to an "agathaumid" ceratopsian, named Manospondylus gigas. This name means "giant porous vertebra", in reference to numerous blood vessel openings in the material. Barnum Brown identified the bones as of a theropod in 1907. As far as 1917, Henry Fairfield Osborn recognized traits shared between Manospondylus and Tyrannosaurus. By this time, the second vertebrae had been lost. Due to the fragmentary nature, he did not synonymize the two, naming the older species indeterminate. In June of 2000, the Black Hills Institute realized over 10% of BHI 6248 was recovered from the Manospondylus locality. Barnum Brown discovered the first documented partial skeleton of Tyrannosaurus remains in 1900 from Wyoming. And in 1902, Brown had found partial material from Hell Creek. This lot contains 34 bones.
Henry Fairfield Osborn, president of the American Museum of Natural History, named Tyrannosaurus rex in 1905. The generic name is derived from the Greek words τυραννος (tyrannos, meaning "tyrant") and σαυρος (sauros, meaning "lizard"). Osborn used the Latin word rex, meaning "king", for the specific name. The full binomial therefore translates to "tyrant lizard king," emphasizing the animal's size and perceived dominance over other species of the time.[62]
Osborn named another specimen, Dynamosaurus, and in 1906, realized the two were named from the same material. He chose Tyrannosaurus as a better name, with the original Dynamosaurus belonging to the Natural History Museum in London. In 1941, the Tyrannosaurus specimen was sold to the Carnegie Museum of Natural History in Pennsylvania for $7000. Dynamosaurus would be later honoured in 2018, with the naming of Dynamoterror, since it had been a "childhood favourite" of the author; Andrew McDonald. From the 1910s-1950s, Barnum's specimens were the only known, since the Great Depression kept scientists from obtaining more.
Dynamosaurus holotype at the London Natural History Museum.
The 1960s marked a great interest in Tyrannosaurus. This results in 42 skeletons, each from 5-80% complete based on bone count, one of the largest known, 'Scotty' MOR 008, discovered in Western North America. This specimen is nearly 15% complete, discovered by Dr. William MacMannis. A reconstructed skull and skeleton is now displayed at the Museum of the Rockies. In the 1990s, many finds are reported, nearly twice than in past years. These include Sue and Stan. When amateur paleontologist Susan Hendrickson discovered Sue in Hell Creek on August 12, 1990, nearly 85% complete, surged a legal battle between who held the fossil in 1997. The litigation settled in favour of land owner Maurice Williams. The Field Museum bought the collection for 7.6 million dollars, being the most expensively sold dinosaur until Stan's auction in 2020. From 1998-1999, the museum spent over 25,000 hours preparing the material, where the remains were shipped to New Jersey to construct a mount and assemble in Chicago. On May 17, 2000, the exhibition was publicized. Countless other specimens, such as Scotty, Stan, Jane, Wyrex, B-Rex and countless others have challenged the paleobiology and paleoecology of Tyrannosaurus. Tyrannosaurus is by far the most well known dinosaur in popular culture among Triceratops and Velociraptor which made their debuts in popular films, shows, novels and other media.
According to the Field Museum, of which Sue is kept at, Sue prefers the they/them pronouns. They further specify that scientists have yet to figure out Sue's gender. When first studied, scientists though Sue as a she, later recalling the statement. Additionally, Sue the Tyrannosaurus was given it's own "suite". Featured attractions are a cast of Sue's mostly complete skeleton, stations where people can touch Sue's skin, here its sounds, and smell its breath. Alongside the skeleton is a separate display case for its gastralia and a realistic life sized model holding an Edmontosaurus nicknamed "fleshy" in its jaws. In 2022, G.S. Paul et al. published their views that Tyrannosaurus formed three species: T. imperator, T. regina and T. rex. This was met with backlash.
Rumours[]
UCMP 137538 is a large (13-centimeter-long) left pedal phalanx assigned to theropoda. It has previously been assigned to Tyrannosaurus, however, it has been rumoured it may have actually been a therizinosaur. It is impossible to tell how large this individual was, since remains, especially in Tyrannosaurus, since they can proportionally vary in specimens, Scaling it based on FMNH PR2081 (Sue) places it at 14+ meters, a gigantic size. However, scaling it with other specimens yields a size much smaller. It was assigned to Tyrannosaurus due to time and location and how it was one of the only large Maastrichtian-aged North American theropod. Additionally, it has been said it may not even be a foot bone[63]. Rumours of a large Hell Creek caenagnathid (once thought to be Gigantoraptor) were once present, which led too people believing that taxon was not the only animal to have migrated to North America, which has been disproven. If it were 14-15 meters long, this would fall within the range of Therizinosaurus, with trackways from the Harebell (same age) and Prince Creek (older age) proving therizinosaurs existed at this time and place[64]. At one point, a Tyrannosaurus astragalus was mistaken by Welles and Long as therizinosaur, but Russel and Manabe (2002) reclassified it as a Tyrannosaurus quadrate[65][66]. Since, the true identity of UCMP 137538 is still unknown, but rumours of a Hell Creek therizinosaur persisted[67]. However, UCMP 137538 was reexamined some time later. The authors noted it most resembled tyrannosaurs and reassigned it to Tyrannosaurus, with evidence for tyrannosaur cannibalism being observed[68].
Tyrannosaur tracks from the Hell Creek Formation were once thought to have been of a massive oviraptorosaur. This was speculated to be most similar to Gigantoraptor or Wakinyatanka, estimated to have reached 2.7 meters. However, a tibia found near the trackways have often been assigned to the same animal. However, the material is likely of a juvenile tyrannosaurid, even more likely a Tyrannosaurus[69][70].
Sue[]
"Sue" the Tyrannosaurus, Field Museum of Natural History, Chicago, showing the forelimbs. The 'wishbone' is between the forelimbs.
Sue Hendrickson, amateur paleontologist, discovered the most complete (more than 90%) and, until 2001, the largest, Tyrannosaurus fossil skeleton known in the Hell Creek Formation near Faith, South Dakota, on 12 August 1990. This Tyrannosaurus, nicknamed "Sue" in her honor, was the object of a legal battle over its ownership. In 1997 this was settled in favor of Maurice Williams, the original land owner, and the fossil collection was sold at auction for USD 7.6 million, making it the most expensive dinosaur skeleton to date. It has now been reassembled and is currently exhibited at the Field Museum of Natural History. A study of this specimen's fossilized bones showed that "Sue" reached full size at age 19 and died at age 28, the longest any tyrannosaur is known to have lived.[71] The "Sue" specimen apparently died from a massive bite to the head, which could only have been inflicted by another tyrannosaur.[72]
Paleoecology[]
Fauna of Hell Creek (Tyrannosaurus in dark red, left).
Tyrannosaurus rex would have served the role as apex predator in its environment. In this case, the environment of Hell Creek during the Maastrichtian would have resembled northern Florida as a warm, moist delta ecosystem with tropical plants growing in swamps and floodplains. During this point in Earth's history the Western Interior Seaway was receding and where there was once ocean a few million years earlier there was now only river systems and a coastal plain.
Tyrannosaurus and other animals of the Hell Creek Formation
Of all the known fauna in the area, Tyrannosaurus makes up around a quarter of all fossils found in Hell Creek, which is surprisingly high for an apex predator, though there could be bias in the fossil record with larger animals preserving better than smaller ones. Living alongside Tyrannosaurus in these fluvial habitats were the iconic three-horned Triceratops, which were the most plentiful animal in the area and would have been the main source of nutrition for Tyrannosaurus. The large hadrosaur Edmontosaurus would have migrated into Hell Creek fairly regularly and served as another favorite prey item for the local tyrannosaur. Other dinosaur residents would have included the armored club-tailed Ankylosaurus, the dome-headed Pachycephalosaurus, the ostrich-like Ornithomimus and the more nimble Thescelosaurus. Among T. rex's carnivorous dinosaur competition, there was the dromaeosaur Acheroraptor, the large oviraptorosaur Anzu, and the troodontid Pectinodon.
While mammals were relatively rare in the area, Didelphodon was a relatively large one that lived alongside all of these dinosaurs. Because the environment was so tropical, Hell Creek would also have supported many animals that require a more warm environment such as crocodilians, turtles, and fish such as gar, sturgeon and even freshwater rays. Specimens of a freshwater mosasaur have also been described to have come from the same deposits as T. rex. Although it didn't live in Hell Creek itself, the gigantic sauropod Alamosaurus was contemporaneous with Tyrannosaurus and fossil evidence suggests that they would have even fed on these massive animals if given the opportunity, as bite marks and tyrannosaur teeth have been found with Alamosaurus bones. As top predator, it would have been T. rex's job to make sure the weak and sick individuals of these herbivores were taken out so the herd populations would be healthy and not overrun the entire ecosystem, so it would have acted as a keystone species. There would have been many deciduous and coniferous trees and made dense forests in Hell Creek. These large plants would have made good places for hiding from prey to ambush (as Tyrannosaurus was suspected to do) or rest in the shade on a hot day. It is believed that instead of four distinct seasons like in modern-day western North America, there would only have been a dry season and a rainy season similar to the African Savannah. The average temperature for Hell Creek would have been much warmer and wetter than the average climate in the same region today. Because the environment was a fluvial one, most fossil remains found have been disarticulated. Tyrannosaurus and its cohorts were among the last non-avian dinosaurs, as Hell Creek goes all the way to the Cretaceous-Paleogene boundary where it is believed an asteroid the size of Mt. Everest crashed into the Yucatan Peninsula and set off a chain of events that would ultimately end in the mass extinction.
Cultural Influence[]
Since it was first described in 1905, Tyrannosaurus rex has become the most widely recognized dinosaur in popular culture. It is the only dinosaur which is routinely referred to by its full scientific name (Tyrannosaurus rex) among the general public, and the scientific abbreviation T. rex has also come into wide usage (commonly misspelled "T-Rex").[73] Robert T. Bakker notes this in The Dinosaur Heresies and explains that a name like "Tyrannosaurus rex is just irresistible to the tongue."[5]
General Impact[]
Tyrannosaurus rex is unique among dinosaurs in its place in modern culture; paleontologist Robert Bakker has called it "the most popular dinosaur among people of all ages, all cultures, and all nationalities".[74] From the beginning, it was embraced by the public. Henry Fairfield Osborn billed it the greatest hunter to have ever walked the earth. He stated in 1905,[75]
In 1942, Charles R. Knight painted a mural incorporating Tyrannosaurus facing a Triceratops in the Field Museum of Natural History for the National Geographic Society, establishing the two dinosaurs as enemies in popular thought;[76] paleontologist Phil Currie cites this mural as one of his inspirations to study dinosaurs.[75] Bakker said of the imagined rivalry between Tyrannosaurus and Triceratops, "No matchup between predator and prey has ever been more dramatic. It’s somehow fitting that those two massive antagonists lived out their co-evolutionary belligerence through the very last days of the very last epoch of the Age of Dinosaurs."[76]
Notable Specimens[]
The "Sue" specimen, stored in the Field Museum of Natural History, Chicago
Sue (FMNH PR2081):[]
Perhaps the most famous and most complete T. rex specimen, Sue is also among the largest and was known to be 12.35 m (40 ft) long. It was found in the badlands of South Dakota in 1990 by Susan Hendrickson (who the animal was named after) and is over 90% complete. After years of legal disputes between the paleontologists who found the skeleton and the owner of the land it was found on, Sue sold for over $8 million to the Field Museum of Chicago and is now where it currently resides on display for the world to see. Along with being one of the largest and most complete T. rex specimens, Sue is also one of the oldest at 28 years of age. By now it was already showing signs of aging with arthritis being visible in the caudal (tail) vertebrae. Other pathologies found on Sue include healed rib fractures, healed infected broken leg bones, bites taken out of its vertebrae by other tyrannosaurs, and even a disease that caused unnatural holes to form in its jaw, which would have made eating incredibly painful and is believed to be the cause of its death. All of this indicates that even the most infamous predator in history would have struggled to survive.
Scotty (RSM P2523.8):[]
Scotty skeleton
Scotty was discovered in Saskatchewan, Canada in 1991 by Robert Gebhardt. Phillip J. Currie and his team excavated the rest of the skeleton and started preparation in the Royal Saskatchewan Museum from there. Scotty was named after the bottle of scotch that was for celebration once the bones had been identified as belonging to T. rex. Once the matrix had been completely cleaned from the bones, analysis was able to be done on them and found that the skeleton was around 70% complete and likely belonged to a Tyrannosaurus that was bigger than any that had been seen before. Estimates put Scotty slightly outsizing Sue at 10-11 tonnes in weight, 12.4 m long and 3.9 m tall. Scotty is also significant for Canada because not only is it the biggest T. rex found from there, it's the biggest dinosaur found in the country period.
B-Rex (MOR 1125):[]
T.rex skeleton in Carnegie Museum of Natural History
In 2000, experienced paleontologist Bob Harmon from Museum of the Rockies was digging in Charles M. Russell National Wildlife Refuge in Garfield County, Montana when he saw a bone sticking out of a steep cliffside. When it was found that the bones belonged to a Tyrannosaurus, it was nicknamed "Bob Rex" or "B-Rex" after the paleontologist who found her. Unfortunately, the fossil had to be split in order for it to be transported, however this allowed for some interesting discoveries to be made. Paleontologist Mary Schweitzer decided to take other opportunity of this situation and tried dissolving a piece of the fossilized bone in acid to see what would happen. As it turned out, when inspected under a microscope, Schweitzer found out that some of the fossils were elastic and resembled soft tissue such as blood vessels. This was the first sign of soft tissue in dinosaur fossils of any kind that had been found. Later on after further study, it was found that the soft tissue was actually medullary tissue, which is what is found in female birds that are about to lay eggs, indicating that B-Rex was female. This also was further indication of how closely T. rex, and by extension dinosaurs, were to birds. Interestingly, histology showed that B-Rex was only a subadult when she died, which suggested that T. rex didn't have to be skeletally mature to be sexually mature, and also that B-Rex was in the middle of laying eggs when she mysteriously died. Only about 37% of the skeleton was found (including nearly a complete skull), and what was found doesn't seem to indicate any injuries that would indicate how she passed away prematurely.
JPInstitute.com Description[]
Probably the most famous of all dinosaurs, T. rex was probably the fiercest meat eater that ever lived. At more than 45 feet in length, it was huge and had the most powerful head of any dinosaur. It also had the biggest teeth of any dinosaur - teeth that were not only sharp and cutting edged, but also thick and strong, capable of crushing bones.
After many millions of years of evolution, nature arrived at T. rex, an almost perfect killing machine. It had large feet to help it run quickly through the swampy environment in which it lived. Although it had very short arms, it didn't need its arms to be an effective and efficient killer. It had enormous strength in its jaws; it could bite right through the frill of a Triceratops or into the back of a hadrosaur. In fact, the only thing that a T. rex had to fear was another T. rex. Most of the scars and wounds found on fossil bones of these great creatures seem to come from others of its kind.
T. rex is very well known, with more than 30 individual specimens having been found. Less than half of these had any significant amount of the fossil, but it still gives us a very good picture of these creatures. The most famous of the fossils of this creature is "Sue" which is now on display at the Field Museum in Chicago. Sue is about 42 feet long; her largest tooth is almost 13 inches.
T. rex is a good example of how our thinking about dinosaurs has changed based on how much we have learned. Back in 1915 when the first skeleton was mounted, most people thought it was a slow beast that dragged its tail along the ground. This view was partially because it would have been very expensive to mount it any other way, and scientists weren't sure how it looked in life. Now, scientists are confident that they understand how T. rex and other dinosaurs looked and lived. T. rex probably walked and ran with its back and tail parallel to the ground, its massive legs and hips a fulcrum for its body. It was an active beast, and recent evidence strongly suggests it was warm blooded.
It has recently been debated as to whether T. rex was strictly a hunter or strictly a scavenger. Their is evidence to both sides of this debate and most scientists believe that T. rex was both an effective hunter and an opportunistic scavenger.
Dinosaur Field Guide Description[]
Tyrannosaurus ("tyrant lizard") is one of the most well-known of all dinosaurs, It is no longer considered the largest of the theropods (see Giganotosaurus), but it is certainly one of the fiercest and most powerful. Tyrannosaurus is the last and largest of the tyrannosaurs, or tyrant dinosaurs. Like other tyrant dinosaurs, Tyrannosaurus has very short arms with only two fingers. Although these were probably useless while hunting, its jaws were not; Tyrannosaurus has an enormous skull armed with teeth the size of bananas! Unlike the teeth of most meat-eaters, tyrant dinosaur teeth are very thick and capable of crushing bones. The skull and neck bones show that T. rex had the largest neck muscles of any meat-eating dinosaur. It probably used its strong neck to twist and pull off big chunks of meat that it grasped with its jaws. Tyrannosaurus could bite with extremely strong force one fossilized skeleton shows that it crushed and swallowed the bones of a smaller plant-eating dinosaur. Most dinosaurs, in general, had eyes facing sideways, which allowed them to see all around themselves. The eyes of Tyrannosaurus, though, faced forward so it could focus better on a single object and tell precisely how far away it was.
This would be very useful for a hunter-especially one that had to fight Triceratops, one of the most dangerous plant-eating dinosaurs of all. The legs of the tyrant dinosaurs were long and slender for their size, allowing them to chase down the horned dinosaurs and duckbills that were the most common plant-eaters of their time. In fact, a specimen of the duckbill Edmontosaurus shows a bite mark taken out of its tail that matches the bite of Tyrannosaurus. Because this bite was healed, we know that the Edmontosaurus managed to get away from its attacker! Although some people think that the female Tyrannosaurus was larger than the male, there is no real evidence for this. Indeed, paleontologists do not yet know how to tell a male Tyrannosaurus from a female from just the skeleton. It is known, though, that Tyrannosaurus led a rough life. Some specimens show many broken bones that had healed over.[77]
Fun Facts[]
A fossilized T. rex dropping was found in Saskatchewan, Canada, in 1995. It was filled with the broken and digested bones of a plant-eating dinosaur. The dropping was the size of a loaf of bread!
Trivia[]
Tyrannosaurus had the biggest brain of any dinosaur known.
Gallery[]
Fact Card[]
Download a flash card to cut out and quiz your friends: File:Dftyran.pdf
Related Articles[]
Appearance in Jurassic Park and other media[]
Jurassic Park[]
Tyrannosaurus rex has arguably made its most iconic role in the movie Jurassic Park (1993) and all of its sequels such as The Lost World: Jurassic Park (1997), Jurassic Park III (2001), Jurassic World (2015), Jurassic World: Fallen Kingdom (2018), and Jurassic World: Dominion (2022) as well as both of the original novels by Michael Crichton. It has acted as a powerful carnivore that often saves the main protagonists (most notably near the end of the movie) and occasionally fights another carnivore that is typically portrayed as a villain (examples include Giganotosaurus and Indominus rex). The most notable Tyrannosaurus from the Jurassic series is Rexy, appearing since the first installment all the way to Dominion, with the only movies he wasn't featured in being The Lost World and Jurassic Park III. Other notable Tyrannosaurus are Buck, Doe, and their Tyrannosaurus all from The Lost World, with Buck and Doe repearing in Dominion, and Bull, a younger adult from Jurassic Park 3 most popular for dying against the Spinosaurus. There are also two recurring Tyrannosaurus in the Netflix tie-in show Camp Cretaceous, a mother-daughter duo known as Big Eatie and Little Eatie.
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The Land Before Time[]
In both the films and television series, Tyrannosaurus plays an important role in sequences involving predators, similarly to the T. rex in Jurassic Park. There are exceptions to T. rex being portrayed in antagonistic lights, however; the character Chomper is a Tyrannosaurus who is a member of the Prehistoric Pals.
As is the case for all carnivorous dinosaurs in the series, though some others have more specific terms, the herbivorous characters simply refer to Tyrannosaurus as "sharpteeth".
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We're Back! A Dinosaur's Story[]
Links[]
https://web.archive.org/web/20080517023754/http://kids.yahoo.com/dinosaurs/49--Tyrannosaurus
References[]
- ↑ https://richmond.com/sue-the-largest-and-most-complete-t-rex-fossil-ever-discovered/article_3c495463-4e8b-588e-a17c-e14e67f494a8.html
- ↑ Sue's vital statistics Sue at the Field Museum. Field Museum of Natural History.
- ↑ Henderson, DM, 1999. Estimating the masses and centers of mass of extinct animals by 3-D mathematical slicing, from the Journal of Paleobiology, vol. 25, issue 1, pp. 88–106 [1].
- ↑ Anderson, JF and Hall-Martin AJ, Russell, Dale A. 1985. Long bone circumference and weight in mammals, birds and dinosaurs, from the Journal of Zoology, vol. 207, issue 1, pp. 53–61.
- ↑ 5.0 5.1 Bakker, Robert T., 1986. The Dinosaur Heresies. New York, Kensington Publishing, ISBN 0-688-04287-2
- ↑ Farlow, James O., Smith MB, & Robinson, JM, 1995. Body mass, bone "strength indicator", and cursorial potential of Tyrannosaurus rex, from the Journal of Vertebrate Paleontology, vol. 15, issue 4, pp. 713–725. [2]
- ↑ Seebacher, Frank. 2001. A new method to calculate allometric length-mass relationships of dinosaurs, from the Journal of Vertebrate Paleontology, vol. 21, issue 1, pp. 51–60.
- ↑ Christiansen, Per & Fariña, Richard A., 2004. Mass prediction in theropod dinosaurs, from the Journal of Historical Biology, vol. 16, issues 2-4, pp. 85–92.
- ↑ 9.0 9.1 Erickson, Gregory M., Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; & Brochu, Christopher A. 2004. Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs, from the Journal of Nature, vol. 430, issue 7001, pp. 772–775. Cite error: Invalid
<ref>tag; name "ericksonetal2004" defined multiple times with different content - ↑ dal Sasso, Cristiano and Maganuco, Simone; Buffetaut, Eric; & Mendez, Marcos A. 2005. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities, from the Journal of Vertebrate Paleontology vol. 25, issue 4, pp. 888–896. [3]
- ↑ Calvo, Jorge O., and Rodolfo Coria, 1998, December. New specimen of Giganotosaurus carolinii (Coria & Salgado, 1995), supports it as the as the largest theropod ever found, from the Journal of Gaia Revista de Geociências, vol. 15, pp. 117–122. [4]
- ↑ 12.00 12.01 12.02 12.03 12.04 12.05 12.06 12.07 12.08 12.09 12.10 12.11 12.12 12.13 https://en.wikipedia.org/wiki/Tyrannosaurus
- ↑ Philip J. Currie, Jørn H. Hurum and Karol Sabath. 2003. Skull structure and evolution in tyrannosaurid dinosaurs, from the Journal of Acta Palaeontologica Polonica, vol. 48, issue 2. pp. 227–234. [5]
- ↑ David B. Weishampel, Peter Dodson and Halszka Osmólska, The dinosauria. University of California Press, in Berkeley, 2004. pp. 111–136, ISBN 0-520-24209-2 Chapter: Tyrannosauroidea, Thomas R., Jr. Holtz.
- ↑ Paul, Gregory S. Predatory dinosaurs of the world: a complete illustrated guide. Simon and Schuster, in New York. 1988. ISBN 0-671-61946-2
- ↑ Holtz, Thomas R., 1994. The Phylogenetic Position of the Tyrannosauridae: Implications for Theropod Systematics, from the Journal of Palaeontology, vol. 68, issue 5, pp. 1100–1117 http://www.jstor.org/pss/1306180
- ↑ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5493735/
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- ↑ https://gizmodo.com/2-5-billion-t-rex-may-have-roamed-earth-1846691923?utm_medium=sharefromsite&utm_source=gizmodo_twitter
- ↑ https://wbng.com/2021/04/15/study-about-2-5-billion-t-rex-roamed-earth-but-not-at-once/
- ↑ https://abcnews.go.com/Technology/wireStory/study-25-billion-rex-roamed-earth-77098450
- ↑ https://fox40.com/news/national-and-world-news/study-about-2-5-billion-t-rex-roamed-earth-but-not-at-once/
- ↑ https://www.sciencefocus.com/news/t-rex-teens-may-have-driven-medium-sized-dinosaur-species-extinct/amp/
- ↑ https://onlinelibrary.wiley.com/doi/10.1111/pala.12648
- ↑ Leidy, J, 1865. Memoir on the extinct reptiles of the Cretaceous formations of the United States, from the journal of Smithsonian Contributions to Knowledge, vol. 14, pp. 1–135.
- ↑ Tyrannosaurus, from the American Museum of Natural History. Retrieved on January 25th, 2009.
- ↑ Newman, BH, 1970. "Stance and gait in the flesh-eating Tyrannosaurus", from the Biological Journal of the Linnean Society, vol. 2, pp. 119–123.
- ↑ https://www-nature-com.libaccess.lib.mcmaster.ca/articles/s41598-020-75731-0
- ↑ The real sound of a T-Rex
- ↑ https://news.utexas.edu/2016/07/11/dinosaurs-may-have-cooed-like-doves/#:~:text=Closed%2Dmouth%20vocalizations%20are%20sounds,exhale%20through%20the%20open%20beak.
- ↑ https://sauriangame.squarespace.com/blog/2018/9/20/tyrannosaurus-redesign-2018
- ↑ https://eartharchives.org/articles/is-the-tyrannosaur-feather-debate-really-over/index.html
- ↑ https://www.cbc.ca/news/canada/saskatchewan/sask-rare-find-in-trex-fossil-1.6435826
- ↑ https://www.sciencedirect.com/science/article/abs/pii/S0012825221001008
- ↑ https://globalnews.ca/news/8702275/scientists-worlds-largest-t-rex-dinosaurs-evolution/
- ↑ https://www.researchgate.net/publication/348002331_TRACKS_IN_THE_UPPER_CRETACEOUS_OF_THE_RATON_BASIN_POSSIBLY_SHOW_TYRANNOSAURID_RISING_FROM_A_PRONE_POSITION
- ↑ https://peerj.com/articles/11450/
- ↑ https://phys.org/news/2017-07-tyrannosaurus-rex-couldnt.html
- ↑ https://www.washingtonpost.com/news/speaking-of-science/wp/2017/07/19/tyrannosaurus-rex-couldnt-run-but-it-was-a-speedy-walker/
- ↑ https://www.livescience.com/t-rex-slow-walker-tail.html
- ↑ https://edition.cnn.com/2021/04/20/world/t-rex-walked-slowly-study-scn/index.html
- ↑ https://www.businessinsider.com/t-rex-walking-speed-slow-similar-to-humans-study-2021-4
- ↑ https://www.news18.com/news/buzz/on-your-mark-humans-can-probably-outwalk-a-tyrannosaurus-rex-reveals-study-3663092.html
- ↑ https://www.sciencetimes.com/articles/30805/20210422/could-you-outrun-a-t-rex-dinosaur-heres-what-experts-say.htm
- ↑ https://www.nationalgeographic.com/science/article/tyrannosaur-trex-running-speed
- ↑ https://scitechdaily.com/new-biomechanical-model-shows-tyrannosaurus-rex-walked-surprisingly-slowly/
- ↑ https://www.forbes.com/sites/davidbressan/2021/04/23/tyrannosaurus-rex-was-not-a-fast-runner-more-a-slow-walker-simulation-shows/?sh=113d28bf64be
- ↑ https://www.businessinsider.com/t-rex-discoveries-hunted-walked-growth-2021-4?amp
- ↑ https://nautil.us/issue/102/hidden-truths/t-rex-was-a-slacker-rp
- ↑ https://theconversation.com/fat-footed-tyrannosaur-parents-couldnt-keep-up-with-their-skinnier-offspring-fossil-footprints-reveal-154188
- ↑ https://phys.org/news/2021-04-fat-footed-tyrannosaur-parents-skinnier-adolescent.html
- ↑ https://phys.org/news/2021-08-rex-jaw-sensors-fearsome-predator.html
- ↑ https://www.dailymail.co.uk/sciencetech/article-9919241/Fossils-T-rex-complex-nerve-sensors-tips-jaws-study-finds.html
- ↑ https://www.sciencedaily.com/releases/2021/08/210824083443.htm
- ↑ https://scitechdaily.com/t-rexs-huge-jaw-had-nerve-sensors-to-make-it-an-even-more-fearsome-predator/
- ↑ https://twitter.com/suzanahh/status/1611119537109479424
- ↑ https://www.nationalgeographic.com/science/article/did-tyrannosaurs-live-in-groups-experts-discuss-new-fossil-clues
- ↑ https://twitter.com/TetZoo/status/1530165632850972672
- ↑ The First Tyrannosaurus Skeleton, 1905, published by Linda Hall, of the Library of Science, Engineering and Technology. [6].
- ↑ Cite error: Invalid
<ref>tag; no text was provided for refs namedosborn1905 - ↑ http://sauropodomorphlair.blogspot.com/2013/07/how-large-is-ucmp-137538-really.html
- ↑ https://www.researchgate.net/publication/236585180_A_therizinosaur_track_from_the_lower_cantwell_formation_upper_cretaceous_of_denali_national_park_alaska
- ↑ http://theropoddatabase.blogspot.com/2014/11/
- ↑ Ryan and Russell, 2001. Dinosaurs of Alberta (exclusive of Aves). in Tanke and Carpenter (eds). Mesozoic Vertebrate Life. Indiana University Press. 279-297.
- ↑ https://www.deviantart.com/paleop/journal/UCMP-137538-612437302
- ↑ https://www.researchgate.net/publication/47545561_Cannibalism_in_Tyrannosaurus_rex
- ↑ https://www.deviantart.com/randomdinos/art/Stem-Bird-Files-Giant-Hell-Creek-oviraptorosaur-594260152
- ↑ https://en.wikipedia.org/wiki/Wakinyantanka
- ↑ Stokstad, E.,"Bone Study Shows T. rex Bulked Up With Massive Growth Spurt", from the Science journal, (13 August 2004), vol. 305, issue 5686, pp. 930–931. [7].
- ↑ Lessons From A Tyrannosaur: The Ambassadorial Role Of Paleontology, by Brochui, C.A., from the Palaios journal. Vol. 18, issue 6, (December, 2003). [8]. Page: 475.
- ↑ Cite error: Invalid
<ref>tag; no text was provided for refs namedbrochu2003 - ↑ Bakker, Robert. Edited by Fiffer, S. Tyrannosaurus Sue (2000). Publisher: W. H. Freeman & Company, in New York ISBN 0-7167-4017-6 pp. xi-xiv Chapter: Prologue.
- ↑ 75.0 75.1 John "Jack" Horner and Don "Dino" Lessem, The Complete T. Rex (New York: Simon & Schuster, 1993), pages 58-62
- ↑ 76.0 76.1 Bakker, R.T. 1986. The Dinosaur Heresies. New York: Kensington Publishing, p. 240. On that page, Bakker has his own T. rex/Triceratops fight.
- ↑
