Ever since the paleontologist Henry Fairfield Osborn rediscovered the Tyrannosaurus rex in 1905 —it was actually discovered 13 years earlier by Edward Drinker Cope, under the name of Manospondylus gigas , but this name never settled—, this gigantic carnivorous dinosaur became in one of the most famous Exploited to the point of exhaustion in literature, cinema and documentaries, it is often considered the largest carnivore that has walked the earth —an important nuance that de facto excludes marine animals—.
Today we know that Tyrannosaurus rex was not actually the largest carnivore ; others surpassed it in size —such as Giganotosaurus— or in length —such as Spinosaurus— . However, Tyrannosaurus continues to retain its fame and media reign, although there are also those who consider it an overrated dinosaur.
Almost since its discovery, a very intense debate about Tyrannosaurus has been on the table. Was it an active predator , attacking its live prey, knocking it down, and devouring it? Or, on the contrary, were their habits those of a scavenger , who, taking advantage of their large size, stole food from other smaller carnivores? As in any good scientific debate, there are data that seem to confirm both hypotheses.
Tyrannosaurus rex as scavenger
One of the most striking features of more modern tyrannosaurids in general, and perfectly represented in Tyrannosaurus , is the diminutive size of its front legs , compared to body size. Compared to the front legs of other dinosaurs that are known predators, those of the ‘tyrant reptile’ do not seem to have much use. But this argument is not very strong. Examples of predatory animals that do not use their front legs in hunting or that have reduced them abound, among them, Carnotaurus , an animal that we know was a predator —and that had the physiognomy of a runner—.
This brings us to a new, more powerful plot line. Tyrannosaurus rex couldn’t run. No, at least an adult Tyrannosaurus , weighing 6 tons. Estimates based on biomechanical studies indicate that he could only walk, and although his stride was considerably long, his speed would not exceed 20 km/h. This limitation would restrict the predatory activity of Tyrannosaurus to animals at least as slow as it, which generally equates to large, strong animals, which it could doubtlessly bring down. Smaller and weaker prey would be far out of reach. However, it would not represent any limitation in scavenging behavior.
Another argument in favor of this behavior is the peculiar shape of the teeth. Unlike predators, with sharp teeth adapted to tear flesh from even living animals, Tyrannosaurus rex ‘s teeth were conical and robust , and combined with the strong musculature of its jaws, could easily shred bone . This type of structure is very well consistent with the behavior of a scavenger capable of feeding on any leftover meat left by other carnivores, including bones. The presence of bone fragments in coprolites identified as Tyrannosaurus reinforces this hypothesis.
Although perhaps the most powerful argument in favor of the scavenger character of Tyrannosaurus is found in its brain. Studying the cranial cavity, it can be seen that the olfactory lobe was extraordinarily developed . This trait has been compared to that of vultures, probably the current birds with the best sense of smell, and practically the only large animals that are almost exclusively scavengers.
Tyrannosaurus rex as a hunter
Speaking of the senses, another trait that characterized Tyrannosaurus was very well-developed binocular vision. Unlike how it is presented to us in Jurassic Park, this animal’s sense of sight was very sharp, and that can benefit a predatory animal, capable of calculating distances. Of course, Tyrannosaurus ‘s efficient sense of smell can also be a great tool for tracking down prey, and not necessarily carcasses. So do modern wolves.
Regarding the teeth, some clearly hunting animals have teeth with a wide base, such as killer whales or crocodiles. It is true that this combination of teeth and jaw muscles can be used to break bones, and it probably fed on them; which does not mean that they were scavengers. Wolves also feed on the bones of their prey.
One of the best available evidence for the predator hypothesis was the discovery, in 2013, of a Tyrannosaurus tooth embedded in a hadrosaurid vertebra. This detail would not be significant were it not for the fact that the animal survived, and the vertebra had healed, surrounding the missing tooth with healthy bone tissue. This was even presented as “the definitive proof that Tyrannosaurus was a hunter, and not a scavenger”.
What if he had both behaviors?
In biology, reality is rarely black or white. Few animals are exclusively scavengers, most hunters will scavenge if given the opportunity. On the other hand, there are animals that exhibit a mixed behavior: they hunt the prey they can, and steal prey from other predators when they have the chance.
Hyenas are a great example of this behavior—contrary to popular belief, hyenas are top predators that combine scavenging behavior with hunting. Interestingly, hyenas have wide-based teeth, strong jaws capable of breaking bones, a great sense of sight and smell, and compared to other animals in their habitat, they are not the fastest.
And this is currently the most widely accepted hypothesis.
Young Tyrannosaurus had long, graceful legs, which allowed them to run and chase prey. Sight and smell would help them find animals to hunt. As they grew in size and weight, the ability to run disappeared, but it did not prevent them from attacking slow and clumsy prey.
However, these animals would be large and strong, and in some cases, with powerful defenses. It would not be strange if they could survive attacks, nor would it be strange for adult Tyrannosaurus to supplement this diet with carrion stolen from other animals, which they would find thanks to their great sense of smell, and which they would feed on, including bones, thanks to their powerful jaws. After all, few carnivores would have the courage to face such a six-ton beast.
In its youth, Tyrannosaurus was probably more of a predator than a scavenger, and as it grew older, it acquired a more mixed behavior, until, probably in later life, it became a scavenger with occasional hunting activities.
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DePalma, R. A. et al. 2013. Physical evidence of predatory behavior in Tyrannosaurus rex. Proceedings of the National Academy of Sciences, 110(31), 12560-12564. DOI: 10.1073/pnas.1216534110
Hone, D. W. E. et al. 2010. New Information on Scavenging and Selective Feeding Behaviour of Tyrannosaurids. Acta Palaeontologica Polonica, 55(4), 627-634. DOI: 10.4202/app.2009.0133
Sellers, W. I. et al. 2017. Investigating the running abilities of Tyrannosaurus rex using stress-constrained multibody dynamic analysis. PeerJ, 5, e3420. DOI: 10.7717/peerj.3420
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