Tyrannosaurus

Before formal naming or identification, this organism was known as the following on this wiki:
**Hell Creek therizinosaur**, **UCMP 137538** and **AMNH 5027**

## Statistics

### Diet

Carnivorous

*Tyrannosaurus* is an extinct genus of tyrannosaurid theropod dinosaur that lived in North America during the Late Cretaceous.

## 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) . *Tyrannosaurus* is known from many skulls, but the largest is 1.52 meters (5 feet) long. The skull has many fenestrae which lighten it's build, a feature in every dinosaur, especially theropods. However, other than a few features, *Tyrannosaurus*' skull was not like other tyrannosaurid skulls. It's rear is wide and it's rostrum is narrow, a feature that allows great binocular vision. The individual bones that make the skull are massive, and bones like the nasals were fused in a strict space, with many other bones pneumatized to reduce weight. These strengthened the skull as well, a trend in tyrannosaurs toward a more powerful bite, of which Tyrannosaurus easily surpassed all other tyrannosauridae. Opposed to most tyrannosauroids having V-shaped upper jaw tips, *Tyrannosaurus* has a broad U. This adaptation allowed the animal to tear more material from a carcass, with the side effect of more stress on the front teeth.

*Tyrannosaurus* teeth show heterodonty. All four premaxillary teeth of the upper jaw ere closely packed, with a D-shaped cross section, reinforcing ridges and a backwards curve to reduce the risk of damaging or loosing teeth during feeding. Every other tooth were closer in shape to a banana than the dagger-like premaxillary teeth, also with ridges. In the upper jaw, twelve lined each side (when mature), larger than those in the lower jaw, minus teeth in the rear. The largest found was 30.5 centimeters (12 inches) long including the root, being the largest of any carnivorous dinosaur. *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. *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.

*Tyrannosaurus* has a long and heavy tail built to counterbalance the weight of the body and house the large locomotor muscles that connected to the thigh. By the underbelly lined 18-19 pairs of segmented gastralia. The shoulder girdle, in itself, was longer than the entire forelimb. The shoulder blade bears a narrow shaft that exceptionally expanded at the top end. The coracoid is long and rounded. The shoulder blades connected by small furcula. The breast bones were possibly made from cartilag

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.

*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.

## History

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. He writes:

—Barnum Brown
    Henry Fairfield Osborn names a second specimen, this time in 1905. He named it "tyrant lizard king", due to the animal's perceived dominance and size over humans and other dinosaurs. 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.

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. 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. 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. Since, the true identity of UCMP 137538 is still unknown, but rumours of a Hell Creek therizinosaur persisted. 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.

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*.

### Paleoart

Like many other theropods, *Tyrannosaurus* was depicted with a vertical posture akin to a tripod, usually 45° or less at the hip. The tail was depicted as a balance dragging on the floor, similar to kangaroos. In 1865, Joseph Leidy reconstructed *Hadrosaurus*, presenting the first depiction of a bipedal *Tyrannosaurus*. In 1915, Henry Fairfield Osborn commissioned the newly-prepared complete *Tyrannosaurus* mount to have an upright posture. It remained for 77 years, taken down in 1992. By 1970, scientists had figured out such a stance would weaken and dislocate joints, including the hips and spinal column. The mentioned mount inspired many media interpretations until the early 1990s, where mainstream film introduced the active bipedal dinosaur.

## Paleobiology

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. Akin to modern carnivorous animal meat.

    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.

### 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.

### Paleopathology

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 .

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.

### 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.

### Ontogeny

    The identification of juvenile individuals allows us to document the life stages, lifespan and growth rate of *Tyrannosaurus* The smallest is LACM 28471 ("Jordan theropod") was 30 kilograms (66 pounds), compared to one of the largest FMNH PR2081("Sue") weighted ~5650 kilograms (12,460 pounds). Bone histology determined LACM 28471 was 2 years old at death and Sue was 28 years old, which may have been close to the oldest age.

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.

    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 . In 2020, a paper was published on *Nanotyrannus*, showing it was likely a synonym of *Tyrannosaurus* .

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 . Juvenile tyrannosaurus are hypothesized to have driven contemporaneous medium-sized theropods to extinction. 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.

### Integument and Soft Tissue

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 .

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".

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.

Tyrannosaur Genetic Material
 *T. bataar* | ~80 million years ago
 *T. rex* | "Maastrichtian"

### 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. 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 . 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.

### Diet

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.

Specimens from E*dmontosaurus 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.

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.

### Thermoregulation

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.

### 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.

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 .

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 . 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. *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. Other research suggests that adults were slower with forager locamotion, while their young were more nimble.

### Senses

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". 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.

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. Controversially, it may have had a neuron count similar to papions and possibly the ability to develop culture, but this research is disputed.

### Intraspecific Behaviour

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.

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.

### 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.

## Species

### Reassigned Species

* "*T." bataar*?
* "*T." zhuchengensis*?
* *"T." (Nanuqsaurus) hoglundi*
* *"T." (Teratophoneus) curriei*
* *"T." (Daspletosaurus) torosus*
* "T. brinkmani" (suggested)
* *T.* "vannus"
* *T. lanpingensis*/*lanpingi*
* *T. gigas*
* *T. novojilovi*
* *T. stanwinstonorum*/*stanwinstonorus*
* *T. lancensis* (suggested)
* *T. gigantus*
* *T. megragracilis*
* *"T." luanchuanensis*

## Synonyms

* *Tarbosaurus*?
	+ *Raptorex*?
	+ *Maleevosaurus*?
	+ *Shanshanosaurus*?
	+ *Jenghizkhan*?
* *Stygivenator*
* *Dinotyrannus*
* *Dynamosaurus*
* *Manospondylus*
* *Nanotyrannus*
	+ "Clevelanotyrannus"
* "Alamotyrannus"?
* CM 9401?
* Hell Creek therizinosaur
* *T.* (*Daspletosaurus*)
* *T.* (*T.*)
* *Aublysodon amplus*?
* *Deinodon amplus*?
* *T. amplus*
* *Aublysodon cristatus*?
* *Deinodon cristatus*?
* *Stygivenator cristatus*?
* *T. imperiosus*
* *Albertosaurus lancensis*
* *Aublysodon lancensis*
* *Deinodon lancensis*
* *Gorgosaurus lancensis*
* *T. regina*
* *T. imperator* (also a name used for Peck's Rex)

## Notable Specimens

* FMNH PR2081 "Sue": One of the most famous specimens known, 'Sue' (named after Susan "Sue" Hendrickson, who discovered the skeleton). Sue is 98% complete and 41 feet long. Sue has many healed injuries, including holes in the bones, signs of disease in their jaws that overtook them and the dinosaur was 28 years old when they died. It was discovered on August 12, 1990 by Hendrickson. The specimen was auctioned after ownership disputes in October 1997 for 8.3 million dollars. This price has since been dwarfed by another specimen, Stan, being auctioned at 31.8 million dollars on October 7, 2020. Sue has since became a permanent attraction housed in the Field Museum in Chicago.
* RSM P2523.8 "Scotty": Discovered in Saskatchewan, Canada in 1991, 'Scotty' was named after the bottle of scotch the excavation team celebrated with. Scotty is 8.8 pounds heavy, outsizing Sue. Scotty was 70% complete upon discovery.
* MOR 1125 "B-Rex": Discovered by Jack Horner, this specimen preserved soft tissue, which shows that dinosaurs had a birth cycle like that of birds. B-Rex may show signs that the individual was a female, based upon the wider hips allowing for egg passage and modified tail bones to allow for said modifications.
* BHI 3033 "Stan": Discovered in South Dakota in 1987, named after Stan Sacrinson, 'Stan' is now the largest *Tyrannosaurus* known. Stan is 70% complete and was described at the Black Hills Institute, of which the skeleton stayed for several years. However, the specimen was put up for auction in 2020, being sold for about $31.8 million dollars. In 2022, National Geographic writer Michael Greshko tracked down who Stan was sold to by looking at export statistics to identify spikes in money that closely match the price it was sold for. He found that it was heading to the Natural History Museum Abu Dhabi according to records from March 2021, an at-the-time un-built complex that was planned to cover 377,000 square feet with science facilities and staff. He also recovered records stating how heavy each shipment was, with the crates assumed to be Stan weighed in at 5100 kilograms, a plausible weight.

* BMRP 2002.4.1 "Jane": A juvenile *Tyrannosaurus* (*Nanotyrannus*?).
* "Tinker" or "Rocky": An immature *Tyrannosaurus*, described as "one of the best preserved and he is the world’s only teenage *T. rex* found to date"; the second statement is incorrect. This specimen is currently unpublished, and was rebranded to "Rocky" for an exhibition at Dinosaur Museum Altmühltal.
* "Titus": Presented as the first real *Tyrannosaurus* to travel for display at the Wollaton Hall Natural History Museum, it was prepared by Nigel Larkin for over 1 year. It was found in 2018 in Montana, being 20% complete upon discovery. It was restored with black obsidian, being 4 meters tall and 11 meters long. The exhibition was named "Titus: T rex is King", and was never displayed before this exhibit; the exhibit will leave in August 2022.
* CM 9380 (prev. AMNH 973) "Barnum": CM 9380 is the type of T. rex. Barnum Brown discovered the fragmented skeleton used to reconstruct the specimen later. The remaining skeleton was recovered 3 years later. The reconstruction is 11.9 meters long and 7.4–14.6 metric tonnes heavy, with an average of 9.1 metric tonnes. The reconstructed skeleton is mounted in Pittsburgh. Osborn first thought the shortened forelimbs of the specimen were incorrect. However, later studies and the publications of a *Gorgosaurus* specimen would prove otherwise. It was first mounted in a bipedal pose and later altered by Phil Fraley and crew. Michael Holland reconstructed the skull, which is a composite. It is rarely referred to as "Barnum". Paul et al. (2022) misspell this specimen as CM 9340.
* LACM 23844 "Harley Rex": Named after Harley Garbani who directed a crew that discovered it in 1966, a near-complete skull of a large, mature *Tyrannosaurus*. When first put on display in Los Angeles. it was then the largest *Tyrannosaurus* on display, but has since been beaten by larger specimens.
* AMNH 5027/AMNH FR 5027: Along with the holotype, one of the main references for Osborn's early-twentieth-century papers describing *Tyrannosaurus* in detail, with it being the first complete *Tyrannosaurus* skull found. The original is displayed at the American Museum of Natural History in New York City, and casts are displayed in various museums worldwide. It was hypothesized by Peter Larson (*Tyrannosaurus rex*, the Tyrant King, 2008) to represent a new, unnamed species within the genus *Tyrannosaurus*. However, Larson listed no autapomorphies and all studies conclude it is a *Tyrannosaurus rex*. Larson also approves of discredited theories such as *Nanotyrannus**.* The mount displayed at the museum bears legs from a larger specimen, CM 9380, with *Allosaurus* feet, which were once believed to have been model for all theropods[*citation needed*].
* "Zuri": A juvenile *Tyrannosaurus* or "*Nanotyrannus*", known from a near-complete skull consisting of a dentary (HRS08486), an ectopterygoid (HRS08498), a frontal (HRS08607), a jugal (HRS08502), a lacrimal (HRS08496), a maxilla (HRS08438), nasals (HRS08423), prearticulars (HRS08495 and HRS08564), pterygoids (HRS08430 and HRS08444), quadrates (HRS08600 and HRS08614), a quadratojugal (HRS08440), a splenial (HRS08443) and a surangular (HRS08510). It was discovered by Zuri Franco (2001), of which it was named, from the Maastrichtian-aged Stair Quarry of the Lance Formation. It was found with many *Edmontosaurus* remains. The compressed teeth are similar to *Nanotyrannus* morphs, but the quadratojugal lacks a pneumatophore.
* "Metarex": 3D models of each bone were split into 58,000 NFTs, nicknamed "Metarex", and sold. This specimen is apparently to be donated to a museum.
* "Lucy": A skeleton at the University of Kansas that took 4 summers to excavate in Montana. David Burnham and crew nicknamed the skeleton Lucy. Some of her (the individual presumed female) remains are still under preparation, but planned to be displayed with the full skeleton at the school's Natural History Museum. 25% of the skull, 60% of the hip and 45% of the leg were recovered. She died at around 15 years.
* AWMM-IL 2022.9 "Peter": A specimen housed in The Auckland War Memorial Museum. It was discovered from the Lance Formation and made public in 2022. Crushed and shattered remains were likely caused by another *Tyrannosaurus* feeding on Peter near to or at the end of its life. This may represent an extreme case of osteophagy, but it was certainly killed by another *Tyrannosaurus*. Damage is most often found in the femur and tibia, and the damage only matches the bite force of *Tyrannosaurus*, The specimen is 47% complete, with *Knethichnus paralleum* found on both leg bones and smaller tooth scrapes caused by a juvenile across the femur, Erosion on the anterior of the ischium and femur and two ascending lesions on the astragalus (one that penetrates the bone, surrounded by reactive bone) are also paleopathologies observed.

## Classification

*Tyrannosaurus* is the type genus of Tyrannosauroidea, Tyrannosauridae and Tyrannosaurinae. Other tyrannosaurines include *Daspletosaurus* and *Tarbosaurus*. Both have been merged with *Tyrannosaurus* on occasion. Tyrannosauridae was commonly thought to be the descendants of large theropods, namely megalosaurs and carnosaurs, but were recently reclassified as coelurosaurs.

Loewen at al. (2013) recovered the following cladogram:

### Possible New Species

*Tarbosaurus* has been suggested to share enough similarities with *Tyrannosaurus rex* that it should be considered a new species of *Tyrannosaurus*, "*Tyrannosaurus baatar*". The synonymy of *Tarbosaurus* is still a contested issue and certain acedemics support it, while others uphold *Tarbosaurus* as a distinct genus. In 1955, Evengy Maleev named *Tyrannosaurus* *bataar* from Mongolia, and it was classified as *Tarbosaurus bataar* by 1965. However, many phylogenetic analyses place the two as sister taxa, and many still consider them of the same genus. When *Lythronax* was discovered, a clade was formed containing *Tyrannosaurus*, *Tarbosaurus* and *Zhuchengtyrannus*, with *Lythronax* as the sister. Steven Brusatte et al. (2016) suggests *Tyrannosaurus* may have immigrated from Asia, as well as being a possible descendant from *Tarbosaurus*. Various tyrannosaur elements (teeth and a metatarsal) were unearthed in 2001 at a quarry near Zhucheng, Chine. Hu Chengzhi named *Tyrannosaurus zhuchengensis*. However, a right maxilla and left jaw were assigned the genus *Zhuchengtyrannus* in 2001. It is possible the two are synonymous, with *T. zhuchengensis* considered a nomen dubium because the holotype lacks features below Tyrannosaurinae. *T. mcraeensis* and T. "vannus" are all possibly the same species or genus. *Tyrannosaurus* "x" (coined by Bakker) was a designation used in reference to AMNH 5027 being hypothesized to be a new species based on another incisiform in the dentary by Pete Larson (2008). Larson also included MOR 008, "Samson" and SDSM 12047 to this morphotype, but further research denied the new species claim.

A 2022 study by G.S. Paul et al. split the genus into three species: *T. regina* ("queen"), from the Lower Hell Creek, which speciated into *T. rex* and *T. imperator* ("emperor") in the Upper Hell Creek. Though this idea of *Tyrannosaurus* speciating is not controversial and even expected by certain tyrannosaur specialists such as Holtz Jr., the methodology of the study attracted much controversy. Paul et al. use femur robusticity and two, slender incisiform dentary teeth to distinguish *T. imperator* of the 1 incisiform and gracile *T. regina*, both of which are unstable autapomorphies that overlap considerably (unlike the expected uniform arrangement distinct species would bear). Instead, these can be explained by individual variation, ontogeny and paleopathology. The species diagnoses are also credited as using generalities, which indicates that not all specimens bear autapomorphies, and that not every specimen was tested and previous morphometric studies refute claims of distinct species (such as Carr (2020), who analyzes all specimens and finds no grounds for a specific distinction). This idea of cladogenesis producing multiple *Tyrannosaurus* species is an idea Paul has advocated for since the 1980s, but this has already been debunked. Additionally, the only reason they decided to name the new species was due to Paul fearing another scientist would, with one author leaving before the article was published. The publication coined Sue as the holotype of *T. imperator* and placed Nation's *T. rex* as the holotype of *T. regina* (also referring Stan, a lost specimen). The hypothesis is considered likely, considering tyrannosaurs, but this particular study does not likely identify separate species. If the names were to be used, it is noted that referred specimens would call for the resurrection of *T. lancensis* for *T. imperator* and *T, megagracilis* for *T. regina*. Holtz Jr., Dave Hone, Asher Elbein, Darren Naish, Gabriel Ugueto and others teased the paper earlier the day of publication, saying it would be controversial and that it was not about spinosaurs or integument. A 2022 study by Carr et al. used phylogenetics to confirm that the specimens suggested to represent new species do not form separate clusters and thus do not require different species names.

## Paleoecology

*Tyrannosaurus* lived in the Hell Creek Formation during the Late Cretaceous. *Tyrannosaurus* lived during the Lancian faunal stage during the Maastrichtian, Late Cretaceous. It extended northwards to Canada and southwards to New Mexico of Laramidia. *Triceratops* was a major herbivore at this time in the north, while *Alamosaurus* dominated the south. *Tyrannosaurus* is known from inland, coastal subtropical and semi-arid plains environments.

Several notable *Tyrannosaurus* specimens are known from the Hell Creek Formation. It was subtropical - warm and humid - during the Maastrichtian. The area consisted mainly of angiosperms, with *Metasequoia* and *Araicaria*. It lived with *Leptoceratops*, *Torosaurus*, *Triceratops*, *Edmontosaurus annectens*, *Thescelosaurus*, *Ankylosaurus*, *Denversaurus*, *Sphaerotholus*, *Pachycephalosaurus*, *Ornithomimus*, *Struthiomimus*, *Acheroraptor*, *Dakotaraptor*, *Pectinodon* and *Anzu*.

*Tyrannosaurus* is also known from Wyoming's Lance Formation, interpreted as a bayou environment similar to the Gulf Coast. The fauna is very similar to Hell Creek, but *Stuthiomimus* is replaced by *Ornithomimus*. *Leptoceratops* also lived in the area.

In the south, *Tyrannosaurus* lived with *Alamosaurus*, *Torosaurus*, *Bravoceratops*, *Ojoceratops*, *Edmontosaurus*, *Kritosaurus*, a possible *Gryposaurus* species, *Glyptodonpelta*, *Ojoraptosaurus*, and possibly even *Troodon* and *Richardoestesia*. *Quetzalcoatlus* also lived in the area. This area is thought to be mainly semi-arid inland plains (likely) after the Western Interior Seaway levels fell.

*Tyrannosaurus* may have inhabited the Lomas Coloradas Formation of Sonora. Material is lacking, but 6 shed and broken teeth appear to be of *Tyrannosaurus* after thorough comparison. If this is true, *Tyrannosaurus*' range may be more extensive than previously believed. It is possible tyrannosaurs were Asian species, who migrated to North America in the Upper Late Cretaceous.

The areas *Tyrannosaurus* lived in where semi-arid, and were likely covered in forests with brackish river systems. The area surrounded the Western Interior Seaway, which means that the edge of *Tyrannosaurus* territory was lined with beaches. Because so many environments were nearby, animals would often cross over. Animals like *Torosaurus* were likely rare to see in the wild. *Quetzalcoatlus*, a long-distance-flying azhdarchid may have crossed into Hell Creek, alongside the unnamed azhdarchid and pteranodontian that are known to have existed alongside *Tyrannosaurus*. *Tyrannosaurus* took up approximately 24% of main Hell Creek fauna .

## Gallery

### Life Reconstructions

**Credit: Fred Wierum.****Credit: Lindsey Wakefield.****Credit: Max Bellomio on ArtStation.****Credit: Beth Zaiken.****Credit: R.J. Palmer.****Credit: R.J. Palmer.****Credit: Corbin Rainbolt.**Reconstruction of Sue resting.**Credit: Batavotyrannus on DeviantArt.****Credit: DanneArt on DeviantArt.****Credit: TeraTheFeathernazi on DeviantArt.****Credit: r-heinart on DeviantArt.**
### Fossils

The texture of a Tyrannosaurus tooth.View from the inside of *Tyrannosaurus* jaws.A *Tyrannosaurus* wishbone.
### Mounts

Old mount at The Field Museum*Tyrannosaurus* and *Triceratops* mount."Stan" the *Tyrannosaurus* mount, before being auctioned.A juvenile *Tyrannosaurus* specimen.Montana's Dueling Dinos cast.Black Beauty at the Royal Tyrrell."Rocky"."Titus"."Lucy".Mounted skeleton of AMNH 5027.
**Credit: Skye McDavid.**Skull of AMNH 5027 in lateral view.
**Credit: Skye McDavid.**Skull of AMNH 5027 in rostral view.
**Credit: Skye McDavid.**AMNH 5027.
**Credit: Skye McDavid.**AMNH 5027.
**Credit: Skye McDavid.**"Wankel Rex" cast at the Royal Ontario Museum.
**Credit: Clumsystiggy on DeviantArt.**
### Diagrams

**Credit: RandomDinos on DeviantArt.**A diagram showcasing various cranial morphologies during various stages of the animals growth cycle. The skeletal has inaccurate anatomy.Comparison of 2D and 3D tyrannosaurid skulls: 2D being the top row and 3D being the bottom. The adult *Tyrannosaurus* USNM 555000, juvenile *Tyrannosaurus* (or *Nanotyrannus*) BMRP 2002.4.1 and the baby tyrannosaurid known as *Raptorex*; LH PV1.**Credit: Matt Dempsey on Twitter.****Credit: Matt Dempsey on Twitter.****Credit: @TyrannOlivia on Twitter.****Credit: @TyrannOlivia on Twitter.****Credit: @TyrannOlivia on Twitter.**"Zuri".
**Credit: Olof Moleman.**"Peter".

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