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 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 Tyrannosauruss 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 predator or a pure scavenger is as old as the debate about its locomotion. Lambe (1917) described a good skeleton of Tyrannosauruss 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 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 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 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 Tyrannosauruss 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, wolves and 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 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, orcas and crocodiles also had broad-based teeth. Holtz noted the similarities between Tyrannosaurus teeth and those of 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 Tyrannosauruss 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.