Feeding behaviour of Tyrannosaurus on:
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The feeding behaviour of ''Tyrannosaurus rex'' has been studied extensively. The well known attributes of ''T. rex'' (its jaws, legs and overall body design) are often interpreted to be indicative of either a Predation, predatory or scavenging lifestyle, and as such the biomechanics, feeding strategies and diet of ''Tyrannosaurus'' have been subject to much research and debate.
Like other tyrannosaurids, ''Tyrannosaurus rex'' is known to have been carnivorous due primarily to the shape of the teeth. A study conducted by Miriam Reichel of the University of Alberta found that the tyrannosaurs' dissimilar teeth had different uses depending on their size, placement, serrated edge and angle in the mouth. While the teeth at the front were specially designed for gripping and pulling, the teeth at the side of the jaw were meant to puncture, and the teeth at the back were specialized both to slice pieces of prey and to force the slices into the throat. She also proposed that the banana-shaped teeth of ''Tyrannosaurus rex'' were designed to withstand the strain of violently struggling prey which would otherwise snap teeth that were sharp, flat and knife-like.
In a study made by Stephan Lautenschlager and colleagues comparing ''Tyrannosaurus'' to fellow theropods ''Allosaurus'' and ''Erlikosaurus'', it was calculated that ''Tyrannosaurus'' was capable of a maximum jaw gape of around 80 degrees; this enormous jaw gape was a necessary adaptation for a wide range of jaw angles to power the creature's strong bite.
A study by Emily J. Rayfield from the University of Bristol further supported that ''Tyrannosaurus'' used the puncture and pull feeding strategy, where the ''Tyrannosaurus'' would startle its prey with a powerful bite and then drag its teeth back through its prey's flesh and bone. The study found that ''Tyrannosaurus'' had a bony skull that was well-adapted to withstand biting and shearing forces, with strong nasal bones that helped it withstand compression and shearing stresses and lacrimal bones that enabled the skull to withstand a variety of stresses. Her study also found that the maxilla jugal sutures found in ''Tyrannosaurus'' cheeks acted as shock absorbers. These joints had soft tissue that absorbed some of the stresses encountered when biting. This traded some of the skull's durability in return for enabling it to better protect the surrounding bones from damage when biting. The study also found that the skull redirected much of the strain from biting to the ''Tyrannosaurus'' skull's robust nasal bones.
In his 2013 lecture, Thomas R. Holtz Jr. stated that fused nasal bones and the presence of incisors were some of the unique traits of ''Tyrannosaurus'' and its relatives. He stated that most reptiles do not have incisors, having teeth at the front of the jaw that are similar to those in the rest of the jaw, and suggested that these incisors were used to scrape the meat from bones. He also stated that ''Tyrannosaurus'' teeth were different from previous theropods because they were thick from side to side, and while the teeth of many other theropods had roots just as long as the crown, the teeth of ''Tyrannosaurus'' had roots that were twice as long as the crowns. He further states that the teeth of ''Tyrannosaurus'' didn't look like they were for cutting, but instead looked like they were for pulverizing, crushing and piercing.
In 2012, a study of the jaws of ''Tyrannosaurus'' by biomechanical expert Karl Bates of the University of Liverpool and paleontologist Peter Falkingham of the Royal Veterinary College, London, and Brown University was published in ''Biology Letters''. Bates and Falkingham used computer modeling to reconstruct ''Tyrannosaurus''s skull and relevant jaw musculature based on anatomical research on crocodilians and birds. From these reconstructions, it was estimated that ''Tyrannosaurus'' was likely capable of exerting a bite force of between 35 and 57 kN (kilonewtons) (7,800–12,700 pounds force), around ten times as great as the strongest alligator bite. However, other, heavier predators, such as the crocodilian ''Deinosuchus'' and the giant shark megalodon, surpassed this bite in strength, having bite forces of about 100 kN and 180 kN respectively. The study also revealed that a juvenile ''Tyrannosaurus'' had a bite force of no more than 880 pounds force, or 3.9 kN, and that the bite became more powerful as the animal matured. This also supports the theory that juvenile ''Tyrannosaurus'' hunted different prey in a form of niche partitioning so as to avoid competition with the adults.
Additionally, research done by Greg Erikson and Paul Gignac et al. and published in the journal ''Scientific Reports'' indicates that ''Tyrannosaurus'' could bite down with around 8,000 pounds force (36 kN) when feeding, exerting a pressure of 431,000 pounds per square inch (3 gigapascals) with their teeth. This adaptation allowed ''Tyrannosaurus'' to drive open cracks present in bone during repetitive, mammal-like biting and produce high-pressure fracture arcades, leading to catastrophic explosions of some bones and allowing the theropod to fully exploit the carcasses of other dinosaurs such as hadrosaurs and ceratopsians, giving it access to the mineral salts and marrow within bone that other carnivores in the same environment could not take advantage of.
Studies published in 2019 on hadrosaur vertebrae from the Hell Creek Formation that were punctured by the teeth of what appears to be a late-stage juvenile ''Tyrannosaurus'' indicate that despite lacking the bone-crushing adaptations of the adults, young individuals were still capable of using the same bone-puncturing feeding technique as their adult counterparts. The bite force of a juvenile ''Tyrannosaurus'' was later calculated to be around 5.6 kN based on these puncture marks and others on another juvenile ''Tyrannosaurus'' in a study published in 2021.
* Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey. Other paleontologists such as Thomas Holtz Jr. and James Farlow, however, gave examples of animals that do not use their forelimbs to hunt such as wolf, wolves, seriemas and secretarybirds. Holtz later stated that the use of forelimbs are not the only viable way of prey capture giving examples of modern predators such as Canidae, canids and hyaenids (hyenas). He also cited other extinct animals such as the ''Diatryma'' (also known as ''Gastornis'') and Phorusrhacids. Gregory S. Paul cited thylacines as another example.
* ''Tyrannosaurus'' had large olfactory bulbs, suggesting a highly developed sense of smell which could sniff out carcasses over great distances, as modern vultures do. Because vultures are primarily scavengers, it has been suggested that such a highly developed sense of smell may imply that tyrannosaurs were as well. However, Farlow and Holtz have noted that a good sense of smell could also be used to detect live prey as well as for behaviors unrelated to food acquisition. Darla K. Zelenitsky, Francois Therrien and Yoshitsugu Kobayashi also discussed the ''Tyrannosaurus''s sense of smell in their 2009 study and stated that it was not an indication of a particular feeding strategy the animal was using (predator versus scavenger), but indicate that tyrannosaurids such as ''Tyrannosaurus'' were active during low light conditions and may have used their sense of smell to search for food and navigate through large home ranges. In a 2013 lecture, Holtz. also noted that like ''Tyrannosaurus'', Wolf, wolves and Dromaeosauridae, raptors such as ''Velociraptor'' also had a good sense of smell. Others have argued that the primary scavenger hypothesis is implausible because the only modern pure scavengers are large gliding birds, which use their keen senses and energy-efficient gliding to cover vast areas economically. However, researchers from Glasgow concluded that an ecosystem as productive as the current Serengeti would provide sufficient carrion for a large theropod scavenger, although the theropod might have had to be cold-blooded in order to get more calories from carrion than it spent on foraging (see Physiology of dinosaurs#Metabolism, Metabolism of dinosaurs). They also suggested that modern ecosystems like Serengeti have no large terrestrial scavengers because gliding birds now do the job much more efficiently, while large theropods did not face competition for the scavenger ecological niche from gliding birds. However, further research by the same scientists found that the evolution of a terrestrial obligate scavenger was unlikely (read more on Ruxton & Houson's 2004 study below).
* Tyrannosaur teeth could crush bone, and therefore could extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in coprolites (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted to systematically chewing bone like hyenas do to extract marrow. Summary at Gregory Paul also wrote that a bone-crushing bite would also have been advantageous to a predator; providing the extreme bite force to kill prey and later consume it efficiently. Other paleontologists would also find similarities between ''Tyrannosaurus'' teeth and those of other predators. Farlow and Holtz pointed out that like ''Tyrannosaurus'', Killer whale, orcas and crocodiles also had broad-based teeth. Holtz noted the similarities between ''Tyrannosaurus'' teeth and those of Hyena, hyaenids, but further added that all hyaenids are known to kill prey, with the largest (''Crocuta crocuta'') obtaining most of its food through this means. He also notes that hyaenids mainly crunch bone with their molars and premolars. Holtz also pointed out that felids also developed thickened teeth as adaptations to resist contact with bone during prey capture or dispatch as well as during feeding.
* Since at least some of ''Tyrannosaurus''s potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger. On the other hand, recent analyses suggest that ''Tyrannosaurus'', while slower than large modern terrestrial predators, may well have been fast enough to prey on large hadrosaurs and ceratopsians.
Other evidence suggests hunting behavior in ''Tyrannosaurus''. The eye-sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them binocular vision slightly better than that of modern hawks. Horner also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is not obvious why natural selection would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception that Stereopsis, stereoscopic vision provides. In modern animals, binocular vision is found mainly in predators.
A 2021 study focusing on the vision and hearing of the small theropod ''Shuvuuia'', to which ''Tyrannosaurus'' was compared suggests that ''Tyrannosaurus'' was a diurnal animal and would have hunted or scavenged predominantly during daylight hours, a feature it shared with the dromaeosaurid ''Dromaeosaurus'', which was also compared to ''Shuvuuia'' in the study.
Furthermore, fossil evidence of tyrannosaur attacks on other dinosaurs have been discovered. A pair of hadrosaur caudal (tail) vertebrae found in 2007 was described by David Burnham et al. in 2013 has the tip of an adult ''Tyrannosaurus'' tooth embedded in the bone, with evidence of new bone growth that wrapped around the tooth. Burnham and his colleagues suggest that this Edmontosaur had also survived a tyrannosaur attack and that this was further proof that ''Tyrannosaurus'' were predators. Kenneth Carpenter (1998) had also described another specimen of the hadrosaurid ''Edmontosaurus annectens'' (in some newspapers it is misidentified as the similar ''Hadrosaurus'') from Montana as having healed supposed tyrannosaur-inflicted damage on its tail vertebrae; having some of its caudal neural spines mutilated. The fact that the damage seems to have healed suggests that the ''Edmontosaurus'' survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation; however, the damage is ambiguous and not directly attributable to ''Tyrannosaurus''. Another Edmontosaur specimen that is suspected to have survived a tyrannosaur attack had also been previously identified by Bruce Rothschild and Robert DePalma in an article published in the journal "Cretaceous Research". This specimen is described to have fossilized skin showing scars and tooth induced traumas on the skull in the form of large tooth drags, with size and spacing that leaves only ''Tyrannosaurus'' as the only likely assailant. Phil Bell of Pipestone Creek further stated that the skull injuries were consistent with tyrannosaur-bitten bones. There is also evidence for an aggressive interaction between a ''Triceratops'' and a ''Tyrannosaurus'' in the form of partially healed tyrannosaur tooth marks on a ''Triceratops'' brow horn and squamosal (a bone of the neck frill); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor. Since the ''Triceratops'' wounds healed, it is most likely that the ''Triceratops'' survived the encounter and managed to overcome the ''Tyrannosaurus''. Paleontologist Peter Dodson estimated that in a battle against a bull ''Triceratops'', the ''Triceratops'' had the upper hand and would successfully defend itself by inflicting fatal wounds to the ''Tyrannosaurus'' using its sharp horns.
Various studies have also taken into account the ecosystem that ''Tyrannosaurus'' lived in. Some researchers argue that if ''Tyrannosaurus'' were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey were the larger marginocephalians and Ornithopoda, ornithopods. The other tyrannosaurids share so many characteristics that only small Dromaeosauridae, dromaeosaurs and Troodontidae, troodontids remain as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to kleptoparasitism, steal kills from smaller predators. However, a study published in 2011 by Chris Carbone, Samuel T. Turvey and Jon Bielby found that ''Tyrannosaurus'' would have been unable to compete as an obligate scavenger against smaller theropods and it would have been necessary for it to primarily hunt large prey. In addition, a study by Graeme D. Ruxton and David C. Houson in 2004 found that vertebrates would need to be large bodied and capable of soaring flight to be obligate scavengers. This study also suggested the evolution of a terrestrial obligate scavenger was unlikely even with the absence of birds because for terrestrial carnivores there is a lack of strong selection pressure towards becoming an exclusive scavenger. The study further adds that it may always be more advantageous for terrestrial carnivores to be able to retain the flexibility of obtaining food through hunting and scavenging. A census study of the Hell Creek Formation published by John Horner, Mark B. Goodwin and Nathan Myhrvold in 2011 found that because of their relative abundance, tyrannosaurs were more like hyenas: opportunistic feeders that dined on more than just live prey and a specific group of dinosaurs. Riley Black, however, held that this research did not overturn ''Tyrannosaurus''s image as a predator, noting that research has found that spotted hyenas obtained a majority of their food from hunting; scavenging as little as 5% in some locations. He also noted that the census is an imperfect depiction of the area's ecology since various biases in collecting and preservation may have affected the results. For example, ''Tyrannosaurus'' may have regularly destroyed the skeletons of ''Edmontosaurus'' which it preyed upon. Horner, Goodwin and Myhrvold's study, according to, actually shows what most palaeontologists believe; that ''Tyrannosaurus'' was an opportunistic carnivore; an animal that both hunted and scavenged. However, the energetic importance of scavenging in ''Tyrannosaurus'' may have been mainly restricted to juvenile individuals as a recent study has shown that multi-ton theropods would have gained little energy from scavenging after accounting for the energy expended from foraging.
Most paleontologists accept that ''Tyrannosaurus'' was both an active predator and a scavenger like most large carnivores. David Hone of Queen Mary, University of London, for example, wrote in his blog that ancering that it was either predator or scavenger in various papers has been unsatisfactory because it was most likely both. Switek also wrote that ''Tyrannosaurus'' was undoubtedly a predator and a scavenger, and that researchers have objected to the idea that ''Tyrannosaurus ''was an obligate scavenger and that there have only been a few studies to directly support the idea of ''Tyrannosaurus'' as an obligate scavenger. John Hutchinson, writing in his blog state that most scientists agree that ''Tyrannosaurus'' switched between being a predator and scavenger; not turning down a meal either dead or alive.
Various proposals have been made regarding the ways ''Tyrannosaurus'' may have hunted. Though adult tyrannosaurs are often depicted in art and other media as frequently attacking other giant dinosaurs, research suggests this type of behavior would have been rare. As with other carnivorous dinosaurs and modern carnivores in general, ''Tyrannosaurus'' probably preferred to target small prey animals, including juveniles of larger dinosaur species. A 2010 analysis by Hone & Rauhut suggested that this may partially explain the general lack of small and juvenile dinosaur skeletons in the fossil record. Tyrannosaurids like ''Tyrannosaurus'' appear to have been specialized to crush and likely ingest the bones of their prey, and predation of juvenile dinosaurs would therefore have left fewer skeletons to fossilize.
Some studies also suggest that ''Tyrannosaurus'' preferred different prey at different stages of its life. In K. T. Bates and P. L. Falkingham's 2012 study, they found that there was a great disparity between the bite force of adult and juvenile ''Tyrannosaurus''. According to the study, ''Tyrannosaurus'' only gained their powerful bite forces during their adulthood. This, according to the pair, suggest a difference in feeding ecologies between juveniles and adults; that the animals may have fed on different prey items at different stages of their lives. They propose that the powerful bite forces of adults may have allowed them to act as large prey specialists and thereby alleviate competition with younger tyrannosaurs. The juveniles according to the scientists were long-legged runners, but had relatively shallow skulls that were incapable of anchoring the muscles necessary to generate an adult ''Tyrannosaurus''s bite force. However, when the animals grew their jaw muscles grew exponentially to the point that these muscles were huge even for animals of their size. The scientists suggest that juveniles chased after small prey while adults had the power to prey on megaherbivores such as ''Edmontosaurus'' and ''Triceratops''. The scientists call this phenomenon as resource partitioning which would have given ''Tyrannosaurus'' a large evolutionary advantage. Horner, Goodwin and Myhrvold's 2011 census makes a similar proposition, proposing that adult ''Tyrannosaurus'' may not have directly competed with juveniles if the possibility of scavenging increased with size as they aged.
The University of Maryland's Thomas R. Holtz Jr. has proposed that ''Tyrannosaurus'' attacked prey like canids and hyaenids do; seizing and killing prey with the jaws, with limited use of the forelimbs for capture and dispatch. Holtz pointed out that ''Tyrannosaurus'' had stout, strong teeth and a bony palate; both of which would have enabled ''Tyrannosaurus'' to resist greater twisting loads and occasional bone contact than allosaurids or other typical theropods. Holtz elaborated that the incrassate (thickened) teeth of ''Tyrannosaurus'' were mechanically stronger than those of other theropods, with deep roots to withstand lateral forces during predation or feeding with a greater torsional component. Furthermore, ''Tyrannosaurus'' had a solidly built bony secondary palate found at the roof of its mouth that would also have strengthened it against torsional loads, a similar adaptation to that of crocodiles but uncommon amongst other theropods. In a lecture in 2013, Thomas Holtz Jr. would point out that torsion is encountered when biting into struggling prey and ''Tyrannosaurus'' resistance to torsional loads showed that it used a 'puncture and pull' method as opposed to the 'bite and slice' of many other theropods. He would also elaborate that like many reptiles, many dinosaurs did not have a hard palate. ''Tyrannosaurus'', however, had a hard palate, just like mammals and crocodiles. Holtz along with James O. Farlow would also support freelance researcher Gregory S. Paul's suggestion that ''Tyrannosaurus'' could have used hit-and-run attacks on its prey.
Gregory S. Paul has suggested that ''Tyrannosaurus'' was a high-risk predator that also attacked massive and dangerous prey; citing this as a reason tyrannosaurs died young. He would indicate that the fossil evidence of animals that surviving tyrannosaur attacks show that these animals were at least healthy enough to heal from their injuries; even suggesting the possibility that some of them may have been able to kill the attacker. Paul wrote that ''Triceratops'' were probably ''Tyrannosaurus''s most challenging and dangerous prey; with horns and parrot like beaks that they could use for defence, and that ''Tyrannosaurus'' did not attack horned animals such as ''Triceratops'' head-on because that would have maximized the danger while lessening the chance of success. Instead ''Tyrannosaurus'' would attack these prey from behind, attempting to bite either the thigh or the caudofemoralis muscle to disable its prey. The ''Tyrannosaurus'' would have done this through either ambushing or trying to intimidate the horned animals into trying to run away which would have then exposed these animals to attack.
David A. Krauss and John M. Robinson proposed that ''Tyrannosaurus'' could have used a hunting strategy similar in concept to "cow tipping" against ''Triceratops'', where the ''Tyrannosaurus'' would ambush and knock the ''Triceratops'' over to fall on its side. This strategy, according to the Krauss and Robinson could explain the unique characteristics of ''Tyrannosaurus''. ''Tyrannosaurus''s small, yet strong arms could have been adapted to grasp onto the back of Triceratops while pushing with its pectoral region, its large clawed feet would have given it better traction, its large head could have been used to tip the ''Triceratops'' over and its large mouth and bone piercing teeth would have made bites to the side more efficient and deadly. When the ''Triceratops'' had fallen over to its side, ''Tyrannosaurus'' would then bitten it at the rib cage; killing it. Krauss and Robinson backed up their proposal through physical analyses; finding that ''Tyrannosaurus'' moving at moderate speed could have generated enough force to topple ''Triceratops'' and would have only taken 2–3 seconds. Their study suggested that a ''Tyrannosaurus'' impacting the ''Triceratops'' at a conservative estimated speed of 7.5 meters per second would have enabled it to topple ''Triceratops'' without injuring itself, though there could be some variance depending on the sizes of the animals (''Tyrannosaurus'' could have attacked a smaller ''Triceratops''). Furthermore, their study noted that ''Triceratops'' would have experienced some difficulty quickly getting back up from being toppled on to its side. According to the study, modern day analogues of ''Triceratops'' such as rhinoceros, camels and large bovids, experience the same kind of difficulty, taking 3–10 seconds to recover. But ''Triceratops'' may have experienced more difficulty due to its Neck frill, frill. According to the study, ''Tyrannosaurus'' arms were adapted for this strategy, pushing the prey with its chest while gripping it with its arms reduced the chance of the prey slipping away while being pushed. The arms, being short yet strong reduced the chance of joint injury during this struggle. Also having more of the arm's power concentrated on its flexors instead of the extensors, were ideal since it would have had to flex its arms to keep its prey close. When the ''Tyrannosaurus'' is pressed against the side of ''Triceratops'', its arms were at the right height to reach the spine of the ''Triceratops'', providing a place to grip on. Furthermore, Krauss and Robinson suggest that this strategy would have been effective against other large ceratopsians and because the attack was done through an ambush, ''Tyrannosaurus'' would not have needed to compete in speed.
Gregory S. Paul also discussed the defenses that hadrosaurs may have employed against tyrannosaurids such as ''Tyrannosaurus''. Paul stated that duck-billed dinosaurs may have been able to kick out with its heavy footed hindlimbs. When faced with a predator, some duckbills were large and may have been able to use their size for protection, otherwise that the only apparent option for them to escape was to flee at maximum speed while attempting to land kicks on its pursuer. He would write that hadrosaurs, while using its forelimbs for locomotion, may have been able out turn tyrannosaurids. Paul wrote that hadrosaurs may have been gregarious (lived in groups) and may have prioritized trying to lose itself in the herd. He would also note that hadrosaurs were also lower-slung than their predators and may have therefore been able to use their forelimbs to push themselves through heavy vegetation; making it difficult for their predators to deliver effective bites.
A study by Lisa Cooper, Andrew H. Lee, Mark L. Taper and John R. Horner suggested that hadrosaurs may have also protected themselves through their rapid growth rates, growing faster than their predators, thus giving them a size advantage and enabling them to breed early. In ''National Geographic News'', Andrew Lee explained that hadrosaurs and ''Tyrannosaurus'' may have started out the same size when they hatched, but by 5 years of age hadrosaurs would be the size of a cow while ''Tyrannosaurus'' would still be the size of a dog. It would also be stated that the sample hadrosaur in the study, ''Hypacrosaurus'' reached a length 30 feet in 10–12 years. ''Tyrannosaurus'' on the other hand reached a length of 40 feet, but it took more than twice as long to reach that size.
''Tyrannosaurus'' may have had more endurance than hadrosaurs such as ''Edmontosaurus''; though biomechanical studies have shown ''Edmontosaurus'' was the faster animal, its greater speed was only useful over short distances, while ''Tyrannosaurus'', being better equipped for pursuit, likely would be able to, if able to keep the animal in sight, outpace and eventually subdue the hadrosaur once the herbivore tired. Such a strategy would save valuable energy while still allowing the ''Tyrannosaurus'' to actively chase down and kill its intended target.
Gregory S. Paul stated that tyrannosaurids attacked hadrosaurs by targeting the caudofemoralis muscle and thigh muscle to disable their prey's locomotor system, the abdomen to eviscerate their prey and the neck which would have caused the most rapid death by damaging the trachea and major blood vessels.
''Tyrannosaurus'' was once proposed to have had infectious saliva used to kill its prey. This theory was first proposed by William Abler. Abler examined the teeth of tyrannosaurids between each tooth serration; the serrations may have held pieces of carcass with bacteria, giving ''Tyrannosaurus'' a deadly, infectious bite much like the Komodo dragon was originally thought to have. However, Jack Horner regards ''Tyrannosaurus'' tooth serrations as more like cubes in shape than the serrations on a Komodo monitor's teeth, which are rounded. All forms of saliva contain possibly hazardous bacteria, so the prospect of it being used as a method of predation is disputable.
A few studies have also focused on ''Tyrannosaurus'' complex feeding habits. ''Tyrannosaurus'', and most other theropods, probably primarily processed carcasses with lateral shakes of the head, like crocodilians. The head was not as maneuverable as the skulls of allosauroidea, allosauroids, due to flat joints of the neck vertebrae. Eric Snively and Anthony Russell further elaborates in a study published in 2007 that ''Tyrannosaurus'' had a powerful neck that would have enabled it to strike rapidly at prey and take on complex and modulated inertial feeding; a way of feeding used by modern archosaurs that involved the animal ripping away chunks of meat, tossing it into the air and swallowing it. A team of paleontologists, led by Denver Fowler from the University of the Rockies would later discover that ''Tyrannosaurus'' employed a complex feeding strategy to consume ''Triceratops'' after analyzing various specimens. This involved the theropod repositioning and tearing off the head of the dead ''Triceratops'', so that it could consume its meal's nutrient-rich neck muscles. Studies of ''Tyrannosaurus''s teeth have also revealed that the animal's dentition was more complex than previously imagined. Researchers Kirstin Brink, Robert Reisz et al. found that ''Tyrannosaurus'' and other carnivorous theropods were equipped with teeth that were highly complex for carnivores; specialized layers of dentine enlarged the serration on the inside of the tooth structure. This unique structure, found in other large predators from other prehistoric eras, and found only in the modern Komodo dragon today is perfectly designed to handle the stresses of ripping into the flesh and biting into the bones of large prey animals without suffering large amounts of wear. This unique feature allowed theropods such as ''Tyrannosaurus'' to flourish for the entirety of their existence.
More findings have also shed light on how ''Tyrannosaurus'' interacted with each other. When examining Sue (dinosaur), Sue, paleontologist Pete Larson found a broken and healed fibula and tail vertebrae, scarred facial bones and a tooth from another ''Tyrannosaurus'' embedded in a neck vertebra. If correct, these might be strong evidence for aggressive behavior between tyrannosaurs but whether it would have been competition for food and mates or active cannibalism is unclear. However, further recent investigation of these purported wounds has shown that most are infections rather than injuries (or simply damage to the fossil after death) and the few injuries are too general to be indicative of intraspecific conflict.
The feeding behaviour of ''Tyrannosaurus rex'' has been studied extensively. The well known attributes of ''T. rex'' (its jaws, legs and overall body design) are often interpreted to be indicative of either a Predation, predatory or scavenging lifestyle, and as such the biomechanics, feeding strategies and diet of ''Tyrannosaurus'' have been subject to much research and debate.
Feeding
Like other tyrannosaurids, ''Tyrannosaurus rex'' is known to have been carnivorous due primarily to the shape of the teeth. A study conducted by Miriam Reichel of the University of Alberta found that the tyrannosaurs' dissimilar teeth had different uses depending on their size, placement, serrated edge and angle in the mouth. While the teeth at the front were specially designed for gripping and pulling, the teeth at the side of the jaw were meant to puncture, and the teeth at the back were specialized both to slice pieces of prey and to force the slices into the throat. She also proposed that the banana-shaped teeth of ''Tyrannosaurus rex'' were designed to withstand the strain of violently struggling prey which would otherwise snap teeth that were sharp, flat and knife-like.
In a study made by Stephan Lautenschlager and colleagues comparing ''Tyrannosaurus'' to fellow theropods ''Allosaurus'' and ''Erlikosaurus'', it was calculated that ''Tyrannosaurus'' was capable of a maximum jaw gape of around 80 degrees; this enormous jaw gape was a necessary adaptation for a wide range of jaw angles to power the creature's strong bite.
A study by Emily J. Rayfield from the University of Bristol further supported that ''Tyrannosaurus'' used the puncture and pull feeding strategy, where the ''Tyrannosaurus'' would startle its prey with a powerful bite and then drag its teeth back through its prey's flesh and bone. The study found that ''Tyrannosaurus'' had a bony skull that was well-adapted to withstand biting and shearing forces, with strong nasal bones that helped it withstand compression and shearing stresses and lacrimal bones that enabled the skull to withstand a variety of stresses. Her study also found that the maxilla jugal sutures found in ''Tyrannosaurus'' cheeks acted as shock absorbers. These joints had soft tissue that absorbed some of the stresses encountered when biting. This traded some of the skull's durability in return for enabling it to better protect the surrounding bones from damage when biting. The study also found that the skull redirected much of the strain from biting to the ''Tyrannosaurus'' skull's robust nasal bones.
In his 2013 lecture, Thomas R. Holtz Jr. stated that fused nasal bones and the presence of incisors were some of the unique traits of ''Tyrannosaurus'' and its relatives. He stated that most reptiles do not have incisors, having teeth at the front of the jaw that are similar to those in the rest of the jaw, and suggested that these incisors were used to scrape the meat from bones. He also stated that ''Tyrannosaurus'' teeth were different from previous theropods because they were thick from side to side, and while the teeth of many other theropods had roots just as long as the crown, the teeth of ''Tyrannosaurus'' had roots that were twice as long as the crowns. He further states that the teeth of ''Tyrannosaurus'' didn't look like they were for cutting, but instead looked like they were for pulverizing, crushing and piercing.
In 2012, a study of the jaws of ''Tyrannosaurus'' by biomechanical expert Karl Bates of the University of Liverpool and paleontologist Peter Falkingham of the Royal Veterinary College, London, and Brown University was published in ''Biology Letters''. Bates and Falkingham used computer modeling to reconstruct ''Tyrannosaurus''s skull and relevant jaw musculature based on anatomical research on crocodilians and birds. From these reconstructions, it was estimated that ''Tyrannosaurus'' was likely capable of exerting a bite force of between 35 and 57 kN (kilonewtons) (7,800–12,700 pounds force), around ten times as great as the strongest alligator bite. However, other, heavier predators, such as the crocodilian ''Deinosuchus'' and the giant shark megalodon, surpassed this bite in strength, having bite forces of about 100 kN and 180 kN respectively. The study also revealed that a juvenile ''Tyrannosaurus'' had a bite force of no more than 880 pounds force, or 3.9 kN, and that the bite became more powerful as the animal matured. This also supports the theory that juvenile ''Tyrannosaurus'' hunted different prey in a form of niche partitioning so as to avoid competition with the adults.
Additionally, research done by Greg Erikson and Paul Gignac et al. and published in the journal ''Scientific Reports'' indicates that ''Tyrannosaurus'' could bite down with around 8,000 pounds force (36 kN) when feeding, exerting a pressure of 431,000 pounds per square inch (3 gigapascals) with their teeth. This adaptation allowed ''Tyrannosaurus'' to drive open cracks present in bone during repetitive, mammal-like biting and produce high-pressure fracture arcades, leading to catastrophic explosions of some bones and allowing the theropod to fully exploit the carcasses of other dinosaurs such as hadrosaurs and ceratopsians, giving it access to the mineral salts and marrow within bone that other carnivores in the same environment could not take advantage of.
Studies published in 2019 on hadrosaur vertebrae from the Hell Creek Formation that were punctured by the teeth of what appears to be a late-stage juvenile ''Tyrannosaurus'' indicate that despite lacking the bone-crushing adaptations of the adults, young individuals were still capable of using the same bone-puncturing feeding technique as their adult counterparts. The bite force of a juvenile ''Tyrannosaurus'' was later calculated to be around 5.6 kN based on these puncture marks and others on another juvenile ''Tyrannosaurus'' in a study published in 2021.
Scavenging
The debate about whether ''Tyrannosaurus'' was an active predation, predator or a pure scavenger, however, is as old as the debate about its locomotion. Lambe (1917) described a good skeleton of ''Tyrannosaurus''s close relative ''Gorgosaurus'' and concluded that it and therefore also ''Tyrannosaurus'' was a pure scavenger, because the ''Gorgosaurus'' teeth showed hardly any wear. This argument is no longer taken seriously, because theropods replaced their teeth quite rapidly. Ever since the first discovery of ''Tyrannosaurus'' most scientists have speculated that it was a predator; like modern large predators it would readily scavenge or steal another predator's kill if it had the opportunity. Paleontologist Jack Horner (paleontologist), Jack Horner has been a major advocate of the idea that ''Tyrannosaurus'' was exclusively a scavenger and did not engage in active hunting at all, though Horner himself has claimed that he never published this idea in the peer reviewed scientific literature and used it mainly as a tool to teach a popular audience, particularly children, the dangers of making assumptions in science (such as assuming ''T. rex'' was a hunter) without using evidence.Novella, S. "Interview with Jack Horner." The Skeptics Guide to the Universe. 14-OCT-2011. Accessed 24-OCT-2011, http://media.libsyn.com/media/skepticsguide/skepticast2009-10-14.mp3 Nevertheless, Horner presented several arguments in the popular literature to support the pure scavenger hypothesis:
* Tyrannosaur arms are short when compared to other known predators. Horner argues that the arms were too short to make the necessary gripping force to hold on to prey. Other paleontologists such as Thomas Holtz Jr. and James Farlow, however, gave examples of animals that do not use their forelimbs to hunt such as wolf, wolves, seriemas and secretarybirds. Holtz later stated that the use of forelimbs are not the only viable way of prey capture giving examples of modern predators such as Canidae, canids and hyaenids (hyenas). He also cited other extinct animals such as the ''Diatryma'' (also known as ''Gastornis'') and Phorusrhacids. Gregory S. Paul cited thylacines as another example.
* ''Tyrannosaurus'' had large olfactory bulbs, suggesting a highly developed sense of smell which could sniff out carcasses over great distances, as modern vultures do. Because vultures are primarily scavengers, it has been suggested that such a highly developed sense of smell may imply that tyrannosaurs were as well. However, Farlow and Holtz have noted that a good sense of smell could also be used to detect live prey as well as for behaviors unrelated to food acquisition. Darla K. Zelenitsky, Francois Therrien and Yoshitsugu Kobayashi also discussed the ''Tyrannosaurus''s sense of smell in their 2009 study and stated that it was not an indication of a particular feeding strategy the animal was using (predator versus scavenger), but indicate that tyrannosaurids such as ''Tyrannosaurus'' were active during low light conditions and may have used their sense of smell to search for food and navigate through large home ranges. In a 2013 lecture, Holtz. also noted that like ''Tyrannosaurus'', Wolf, wolves and Dromaeosauridae, raptors such as ''Velociraptor'' also had a good sense of smell. Others have argued that the primary scavenger hypothesis is implausible because the only modern pure scavengers are large gliding birds, which use their keen senses and energy-efficient gliding to cover vast areas economically. However, researchers from Glasgow concluded that an ecosystem as productive as the current Serengeti would provide sufficient carrion for a large theropod scavenger, although the theropod might have had to be cold-blooded in order to get more calories from carrion than it spent on foraging (see Physiology of dinosaurs#Metabolism, Metabolism of dinosaurs). They also suggested that modern ecosystems like Serengeti have no large terrestrial scavengers because gliding birds now do the job much more efficiently, while large theropods did not face competition for the scavenger ecological niche from gliding birds. However, further research by the same scientists found that the evolution of a terrestrial obligate scavenger was unlikely (read more on Ruxton & Houson's 2004 study below).
* Tyrannosaur teeth could crush bone, and therefore could extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in coprolites (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted to systematically chewing bone like hyenas do to extract marrow. Summary at Gregory Paul also wrote that a bone-crushing bite would also have been advantageous to a predator; providing the extreme bite force to kill prey and later consume it efficiently. Other paleontologists would also find similarities between ''Tyrannosaurus'' teeth and those of other predators. Farlow and Holtz pointed out that like ''Tyrannosaurus'', Killer whale, orcas and crocodiles also had broad-based teeth. Holtz noted the similarities between ''Tyrannosaurus'' teeth and those of Hyena, hyaenids, but further added that all hyaenids are known to kill prey, with the largest (''Crocuta crocuta'') obtaining most of its food through this means. He also notes that hyaenids mainly crunch bone with their molars and premolars. Holtz also pointed out that felids also developed thickened teeth as adaptations to resist contact with bone during prey capture or dispatch as well as during feeding.
* Since at least some of ''Tyrannosaurus''s potential prey could move quickly, evidence that it walked instead of ran could indicate that it was a scavenger. On the other hand, recent analyses suggest that ''Tyrannosaurus'', while slower than large modern terrestrial predators, may well have been fast enough to prey on large hadrosaurs and ceratopsians.
Other evidence suggests hunting behavior in ''Tyrannosaurus''. The eye-sockets of tyrannosaurs are positioned so that the eyes would point forward, giving them binocular vision slightly better than that of modern hawks. Horner also pointed out that the tyrannosaur lineage had a history of steadily improving binocular vision. It is not obvious why natural selection would have favored this long-term trend if tyrannosaurs had been pure scavengers, which would not have needed the advanced depth perception that Stereopsis, stereoscopic vision provides. In modern animals, binocular vision is found mainly in predators.
A 2021 study focusing on the vision and hearing of the small theropod ''Shuvuuia'', to which ''Tyrannosaurus'' was compared suggests that ''Tyrannosaurus'' was a diurnal animal and would have hunted or scavenged predominantly during daylight hours, a feature it shared with the dromaeosaurid ''Dromaeosaurus'', which was also compared to ''Shuvuuia'' in the study.
Furthermore, fossil evidence of tyrannosaur attacks on other dinosaurs have been discovered. A pair of hadrosaur caudal (tail) vertebrae found in 2007 was described by David Burnham et al. in 2013 has the tip of an adult ''Tyrannosaurus'' tooth embedded in the bone, with evidence of new bone growth that wrapped around the tooth. Burnham and his colleagues suggest that this Edmontosaur had also survived a tyrannosaur attack and that this was further proof that ''Tyrannosaurus'' were predators. Kenneth Carpenter (1998) had also described another specimen of the hadrosaurid ''Edmontosaurus annectens'' (in some newspapers it is misidentified as the similar ''Hadrosaurus'') from Montana as having healed supposed tyrannosaur-inflicted damage on its tail vertebrae; having some of its caudal neural spines mutilated. The fact that the damage seems to have healed suggests that the ''Edmontosaurus'' survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation; however, the damage is ambiguous and not directly attributable to ''Tyrannosaurus''. Another Edmontosaur specimen that is suspected to have survived a tyrannosaur attack had also been previously identified by Bruce Rothschild and Robert DePalma in an article published in the journal "Cretaceous Research". This specimen is described to have fossilized skin showing scars and tooth induced traumas on the skull in the form of large tooth drags, with size and spacing that leaves only ''Tyrannosaurus'' as the only likely assailant. Phil Bell of Pipestone Creek further stated that the skull injuries were consistent with tyrannosaur-bitten bones. There is also evidence for an aggressive interaction between a ''Triceratops'' and a ''Tyrannosaurus'' in the form of partially healed tyrannosaur tooth marks on a ''Triceratops'' brow horn and squamosal (a bone of the neck frill); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor. Since the ''Triceratops'' wounds healed, it is most likely that the ''Triceratops'' survived the encounter and managed to overcome the ''Tyrannosaurus''. Paleontologist Peter Dodson estimated that in a battle against a bull ''Triceratops'', the ''Triceratops'' had the upper hand and would successfully defend itself by inflicting fatal wounds to the ''Tyrannosaurus'' using its sharp horns.
Various studies have also taken into account the ecosystem that ''Tyrannosaurus'' lived in. Some researchers argue that if ''Tyrannosaurus'' were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey were the larger marginocephalians and Ornithopoda, ornithopods. The other tyrannosaurids share so many characteristics that only small Dromaeosauridae, dromaeosaurs and Troodontidae, troodontids remain as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to kleptoparasitism, steal kills from smaller predators. However, a study published in 2011 by Chris Carbone, Samuel T. Turvey and Jon Bielby found that ''Tyrannosaurus'' would have been unable to compete as an obligate scavenger against smaller theropods and it would have been necessary for it to primarily hunt large prey. In addition, a study by Graeme D. Ruxton and David C. Houson in 2004 found that vertebrates would need to be large bodied and capable of soaring flight to be obligate scavengers. This study also suggested the evolution of a terrestrial obligate scavenger was unlikely even with the absence of birds because for terrestrial carnivores there is a lack of strong selection pressure towards becoming an exclusive scavenger. The study further adds that it may always be more advantageous for terrestrial carnivores to be able to retain the flexibility of obtaining food through hunting and scavenging. A census study of the Hell Creek Formation published by John Horner, Mark B. Goodwin and Nathan Myhrvold in 2011 found that because of their relative abundance, tyrannosaurs were more like hyenas: opportunistic feeders that dined on more than just live prey and a specific group of dinosaurs. Riley Black, however, held that this research did not overturn ''Tyrannosaurus''s image as a predator, noting that research has found that spotted hyenas obtained a majority of their food from hunting; scavenging as little as 5% in some locations. He also noted that the census is an imperfect depiction of the area's ecology since various biases in collecting and preservation may have affected the results. For example, ''Tyrannosaurus'' may have regularly destroyed the skeletons of ''Edmontosaurus'' which it preyed upon. Horner, Goodwin and Myhrvold's study, according to, actually shows what most palaeontologists believe; that ''Tyrannosaurus'' was an opportunistic carnivore; an animal that both hunted and scavenged. However, the energetic importance of scavenging in ''Tyrannosaurus'' may have been mainly restricted to juvenile individuals as a recent study has shown that multi-ton theropods would have gained little energy from scavenging after accounting for the energy expended from foraging.
Most paleontologists accept that ''Tyrannosaurus'' was both an active predator and a scavenger like most large carnivores. David Hone of Queen Mary, University of London, for example, wrote in his blog that ancering that it was either predator or scavenger in various papers has been unsatisfactory because it was most likely both. Switek also wrote that ''Tyrannosaurus'' was undoubtedly a predator and a scavenger, and that researchers have objected to the idea that ''Tyrannosaurus ''was an obligate scavenger and that there have only been a few studies to directly support the idea of ''Tyrannosaurus'' as an obligate scavenger. John Hutchinson, writing in his blog state that most scientists agree that ''Tyrannosaurus'' switched between being a predator and scavenger; not turning down a meal either dead or alive.
Hunting strategies
Various proposals have been made regarding the ways ''Tyrannosaurus'' may have hunted. Though adult tyrannosaurs are often depicted in art and other media as frequently attacking other giant dinosaurs, research suggests this type of behavior would have been rare. As with other carnivorous dinosaurs and modern carnivores in general, ''Tyrannosaurus'' probably preferred to target small prey animals, including juveniles of larger dinosaur species. A 2010 analysis by Hone & Rauhut suggested that this may partially explain the general lack of small and juvenile dinosaur skeletons in the fossil record. Tyrannosaurids like ''Tyrannosaurus'' appear to have been specialized to crush and likely ingest the bones of their prey, and predation of juvenile dinosaurs would therefore have left fewer skeletons to fossilize.
Some studies also suggest that ''Tyrannosaurus'' preferred different prey at different stages of its life. In K. T. Bates and P. L. Falkingham's 2012 study, they found that there was a great disparity between the bite force of adult and juvenile ''Tyrannosaurus''. According to the study, ''Tyrannosaurus'' only gained their powerful bite forces during their adulthood. This, according to the pair, suggest a difference in feeding ecologies between juveniles and adults; that the animals may have fed on different prey items at different stages of their lives. They propose that the powerful bite forces of adults may have allowed them to act as large prey specialists and thereby alleviate competition with younger tyrannosaurs. The juveniles according to the scientists were long-legged runners, but had relatively shallow skulls that were incapable of anchoring the muscles necessary to generate an adult ''Tyrannosaurus''s bite force. However, when the animals grew their jaw muscles grew exponentially to the point that these muscles were huge even for animals of their size. The scientists suggest that juveniles chased after small prey while adults had the power to prey on megaherbivores such as ''Edmontosaurus'' and ''Triceratops''. The scientists call this phenomenon as resource partitioning which would have given ''Tyrannosaurus'' a large evolutionary advantage. Horner, Goodwin and Myhrvold's 2011 census makes a similar proposition, proposing that adult ''Tyrannosaurus'' may not have directly competed with juveniles if the possibility of scavenging increased with size as they aged.
The University of Maryland's Thomas R. Holtz Jr. has proposed that ''Tyrannosaurus'' attacked prey like canids and hyaenids do; seizing and killing prey with the jaws, with limited use of the forelimbs for capture and dispatch. Holtz pointed out that ''Tyrannosaurus'' had stout, strong teeth and a bony palate; both of which would have enabled ''Tyrannosaurus'' to resist greater twisting loads and occasional bone contact than allosaurids or other typical theropods. Holtz elaborated that the incrassate (thickened) teeth of ''Tyrannosaurus'' were mechanically stronger than those of other theropods, with deep roots to withstand lateral forces during predation or feeding with a greater torsional component. Furthermore, ''Tyrannosaurus'' had a solidly built bony secondary palate found at the roof of its mouth that would also have strengthened it against torsional loads, a similar adaptation to that of crocodiles but uncommon amongst other theropods. In a lecture in 2013, Thomas Holtz Jr. would point out that torsion is encountered when biting into struggling prey and ''Tyrannosaurus'' resistance to torsional loads showed that it used a 'puncture and pull' method as opposed to the 'bite and slice' of many other theropods. He would also elaborate that like many reptiles, many dinosaurs did not have a hard palate. ''Tyrannosaurus'', however, had a hard palate, just like mammals and crocodiles. Holtz along with James O. Farlow would also support freelance researcher Gregory S. Paul's suggestion that ''Tyrannosaurus'' could have used hit-and-run attacks on its prey.
Gregory S. Paul has suggested that ''Tyrannosaurus'' was a high-risk predator that also attacked massive and dangerous prey; citing this as a reason tyrannosaurs died young. He would indicate that the fossil evidence of animals that surviving tyrannosaur attacks show that these animals were at least healthy enough to heal from their injuries; even suggesting the possibility that some of them may have been able to kill the attacker. Paul wrote that ''Triceratops'' were probably ''Tyrannosaurus''s most challenging and dangerous prey; with horns and parrot like beaks that they could use for defence, and that ''Tyrannosaurus'' did not attack horned animals such as ''Triceratops'' head-on because that would have maximized the danger while lessening the chance of success. Instead ''Tyrannosaurus'' would attack these prey from behind, attempting to bite either the thigh or the caudofemoralis muscle to disable its prey. The ''Tyrannosaurus'' would have done this through either ambushing or trying to intimidate the horned animals into trying to run away which would have then exposed these animals to attack.
David A. Krauss and John M. Robinson proposed that ''Tyrannosaurus'' could have used a hunting strategy similar in concept to "cow tipping" against ''Triceratops'', where the ''Tyrannosaurus'' would ambush and knock the ''Triceratops'' over to fall on its side. This strategy, according to the Krauss and Robinson could explain the unique characteristics of ''Tyrannosaurus''. ''Tyrannosaurus''s small, yet strong arms could have been adapted to grasp onto the back of Triceratops while pushing with its pectoral region, its large clawed feet would have given it better traction, its large head could have been used to tip the ''Triceratops'' over and its large mouth and bone piercing teeth would have made bites to the side more efficient and deadly. When the ''Triceratops'' had fallen over to its side, ''Tyrannosaurus'' would then bitten it at the rib cage; killing it. Krauss and Robinson backed up their proposal through physical analyses; finding that ''Tyrannosaurus'' moving at moderate speed could have generated enough force to topple ''Triceratops'' and would have only taken 2–3 seconds. Their study suggested that a ''Tyrannosaurus'' impacting the ''Triceratops'' at a conservative estimated speed of 7.5 meters per second would have enabled it to topple ''Triceratops'' without injuring itself, though there could be some variance depending on the sizes of the animals (''Tyrannosaurus'' could have attacked a smaller ''Triceratops''). Furthermore, their study noted that ''Triceratops'' would have experienced some difficulty quickly getting back up from being toppled on to its side. According to the study, modern day analogues of ''Triceratops'' such as rhinoceros, camels and large bovids, experience the same kind of difficulty, taking 3–10 seconds to recover. But ''Triceratops'' may have experienced more difficulty due to its Neck frill, frill. According to the study, ''Tyrannosaurus'' arms were adapted for this strategy, pushing the prey with its chest while gripping it with its arms reduced the chance of the prey slipping away while being pushed. The arms, being short yet strong reduced the chance of joint injury during this struggle. Also having more of the arm's power concentrated on its flexors instead of the extensors, were ideal since it would have had to flex its arms to keep its prey close. When the ''Tyrannosaurus'' is pressed against the side of ''Triceratops'', its arms were at the right height to reach the spine of the ''Triceratops'', providing a place to grip on. Furthermore, Krauss and Robinson suggest that this strategy would have been effective against other large ceratopsians and because the attack was done through an ambush, ''Tyrannosaurus'' would not have needed to compete in speed.
Gregory S. Paul also discussed the defenses that hadrosaurs may have employed against tyrannosaurids such as ''Tyrannosaurus''. Paul stated that duck-billed dinosaurs may have been able to kick out with its heavy footed hindlimbs. When faced with a predator, some duckbills were large and may have been able to use their size for protection, otherwise that the only apparent option for them to escape was to flee at maximum speed while attempting to land kicks on its pursuer. He would write that hadrosaurs, while using its forelimbs for locomotion, may have been able out turn tyrannosaurids. Paul wrote that hadrosaurs may have been gregarious (lived in groups) and may have prioritized trying to lose itself in the herd. He would also note that hadrosaurs were also lower-slung than their predators and may have therefore been able to use their forelimbs to push themselves through heavy vegetation; making it difficult for their predators to deliver effective bites.
A study by Lisa Cooper, Andrew H. Lee, Mark L. Taper and John R. Horner suggested that hadrosaurs may have also protected themselves through their rapid growth rates, growing faster than their predators, thus giving them a size advantage and enabling them to breed early. In ''National Geographic News'', Andrew Lee explained that hadrosaurs and ''Tyrannosaurus'' may have started out the same size when they hatched, but by 5 years of age hadrosaurs would be the size of a cow while ''Tyrannosaurus'' would still be the size of a dog. It would also be stated that the sample hadrosaur in the study, ''Hypacrosaurus'' reached a length 30 feet in 10–12 years. ''Tyrannosaurus'' on the other hand reached a length of 40 feet, but it took more than twice as long to reach that size.
''Tyrannosaurus'' may have had more endurance than hadrosaurs such as ''Edmontosaurus''; though biomechanical studies have shown ''Edmontosaurus'' was the faster animal, its greater speed was only useful over short distances, while ''Tyrannosaurus'', being better equipped for pursuit, likely would be able to, if able to keep the animal in sight, outpace and eventually subdue the hadrosaur once the herbivore tired. Such a strategy would save valuable energy while still allowing the ''Tyrannosaurus'' to actively chase down and kill its intended target.
Gregory S. Paul stated that tyrannosaurids attacked hadrosaurs by targeting the caudofemoralis muscle and thigh muscle to disable their prey's locomotor system, the abdomen to eviscerate their prey and the neck which would have caused the most rapid death by damaging the trachea and major blood vessels.
''Tyrannosaurus'' was once proposed to have had infectious saliva used to kill its prey. This theory was first proposed by William Abler. Abler examined the teeth of tyrannosaurids between each tooth serration; the serrations may have held pieces of carcass with bacteria, giving ''Tyrannosaurus'' a deadly, infectious bite much like the Komodo dragon was originally thought to have. However, Jack Horner regards ''Tyrannosaurus'' tooth serrations as more like cubes in shape than the serrations on a Komodo monitor's teeth, which are rounded. All forms of saliva contain possibly hazardous bacteria, so the prospect of it being used as a method of predation is disputable.
Feeding behavior
A few studies have also focused on ''Tyrannosaurus'' complex feeding habits. ''Tyrannosaurus'', and most other theropods, probably primarily processed carcasses with lateral shakes of the head, like crocodilians. The head was not as maneuverable as the skulls of allosauroidea, allosauroids, due to flat joints of the neck vertebrae. Eric Snively and Anthony Russell further elaborates in a study published in 2007 that ''Tyrannosaurus'' had a powerful neck that would have enabled it to strike rapidly at prey and take on complex and modulated inertial feeding; a way of feeding used by modern archosaurs that involved the animal ripping away chunks of meat, tossing it into the air and swallowing it. A team of paleontologists, led by Denver Fowler from the University of the Rockies would later discover that ''Tyrannosaurus'' employed a complex feeding strategy to consume ''Triceratops'' after analyzing various specimens. This involved the theropod repositioning and tearing off the head of the dead ''Triceratops'', so that it could consume its meal's nutrient-rich neck muscles. Studies of ''Tyrannosaurus''s teeth have also revealed that the animal's dentition was more complex than previously imagined. Researchers Kirstin Brink, Robert Reisz et al. found that ''Tyrannosaurus'' and other carnivorous theropods were equipped with teeth that were highly complex for carnivores; specialized layers of dentine enlarged the serration on the inside of the tooth structure. This unique structure, found in other large predators from other prehistoric eras, and found only in the modern Komodo dragon today is perfectly designed to handle the stresses of ripping into the flesh and biting into the bones of large prey animals without suffering large amounts of wear. This unique feature allowed theropods such as ''Tyrannosaurus'' to flourish for the entirety of their existence.
More findings have also shed light on how ''Tyrannosaurus'' interacted with each other. When examining Sue (dinosaur), Sue, paleontologist Pete Larson found a broken and healed fibula and tail vertebrae, scarred facial bones and a tooth from another ''Tyrannosaurus'' embedded in a neck vertebra. If correct, these might be strong evidence for aggressive behavior between tyrannosaurs but whether it would have been competition for food and mates or active cannibalism is unclear. However, further recent investigation of these purported wounds has shown that most are infections rather than injuries (or simply damage to the fossil after death) and the few injuries are too general to be indicative of intraspecific conflict.
Cannibalism
A study from Currie, Horner, Erickson and Longrich in 2010 has been put forward as evidence of cannibalism in the genus ''Tyrannosaurus''. They studied some ''Tyrannosaurus'' specimens with tooth marks in the bones, attributable to the same genus. The tooth marks were identified in the humerus, foot bones and metatarsals, and this was seen as evidence for opportunistic scavenging, rather than wounds caused by intraspecific combat. In a fight, they proposed it would be difficult to reach down to bite in the feet of a rival, making it more likely that the bitemarks were made in a carcass. As the bitemarks were made in body parts with relatively scantly amounts of flesh, it is suggested that the ''Tyrannosaurus'' was feeding on a cadaver in which the more fleshy parts already had been consumed. They were also open to the possibility that other Tyrannosauridae, tyrannosaurids practiced cannibalism.References
{{Reflist Predation Tyrannosaurus Carnivory