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66 million years ago they went out, along with the rest of the dinosaurs, after the impact of a meteorite that caused more than 75% of life on earth. It lived in what is now North America, and ever since Edward Drinker Cope discovered the first specimen in 1892, both its ferocious behavior and certain features of its anatomy continue to intrigue scientists.
And it is that the Tyrannosaurus Rex had strangely short forelimbs, with limited mobility and that, without a doubt, 'do not fit' with the rest of the body of one of the largest predators that have set foot on our planet. With its more than 13 meters long, its enormous skull and the most powerful jaws that have ever existed, the T.
rex was capable of biting with a force that paleontologists estimate between 20.000 and 57.000 newtons. The same, for example, that an elephant exerts on the ground when sitting down. For comparison, suffice it to say that the bite force of a human rarely exceeds 300 newtons.
Why such short arms?
Now, why did the T. Rex have such ridiculously small arms? For more than a century, scientists have been proposing various explanations (for mating, to hold their prey, to return to the animals they attacked...), but for Kevin Padian, a paleontologist at the University of Berkeley, in California, none of them is correct.
In a recent article published in 'Acta Paleontologica Polonica', in fact, Padian maintains that the arms of T. rex are reduced in size to avoid irreparable damage caused by the bite of one of their congeners. Evolution does not maintain a certain physical trait if not for a good reason. And Padian, in order to ask what such short upper limbs could be used for, focuses on finding out what possible benefits they could have for the animal. In his paper, the researcher hypothesizes that T. rex arms 'shrank' to prevent accidental or intentional amputations when a herd of tyrannosaurs lunged at a carcass with their huge heads and bone-crushing teeth.
A 13-meter T. rex, for example, with a 1,5-meter-long skull, had arms nom longer than 90 centimeters. If we apply these proportions to a human being 1,80 meters tall, his arms would barely measure 13 centimeters.
avoiding bites
“What would happen if several adult tyrannosaurs gathered around a carcass? Padian wonders. We would have a mountain of huge skulls, with incredibly powerful jaws and teeth tearing and chewing through flesh and bone right next to each other. And what if one of them thinks the other is getting too close? He could warn her away by cutting off her arm. So reducing the forelimbs could be a big benefit, it's just that they won't be used in predation anyway."
A serious wound has resulted in a bite that can lead to infection, bleeding, shock, and eventually death. In his study, Padian says that the ancestors of tyrannosaurs have longer arms, and therefore their subsequent reduction in size must be for good reason. Furthermore, this reduction did not affect only T. rex, which lived in North America, but also other large carnivorous dinosaurs that lived in Africa, South America, Europe and Asia in different Cretaceous periods, some of them even larger than the Tyrannosaurus Rex.
According to Padian, all the ideas in this regard presented so far “have not been tried or are impossible because they cannot work. And neither hypothesis explains why the arms might get smaller. In all cases, the proposed functions would have been much more effective if they had not been reduced to seeing them as weapons.”
They hunted in packs
The idea proposed in his study occurred to the researcher when other paleontologists found evidence that T.rex was not a solitary hunter, as expected, but often hunted in packs.
Several major site discoveries Over the past 20 years, Padian explains, they show adult and juvenile tyrannosaurs side by side. “Really -he points out- we cannot assume that they lived together or even that they appeared together. We only know that they ended up buried together. But when multiple sites are found where the same thing happens, the signal becomes stronger. And the possibility, which other researchers have already raised, is that they were hunting in a group.
In his study, the Berkeley paleontologist examined and discarded one by one the solutions to the enigma proposed so far. “The arms are simply too short,” he explains. They can't touch each other, they can't reach their mouths, and their mobility is so limited that they can't stretch very far, either forward or up. The huge head and neck are way ahead of them and form the kind of death machine we saw in Jurassic Park." Twenty years ago, a team of paleontologists analyzed the arms planted there with the hypothesis that T. rex could have lifted about 181 kg with them. "But the thing," says Padians, "is that you couldn't get close enough to anything to pick it up."
current analogies
Padian's hypothesis has analogies with some real animals, such as the giant Indonesian Komodo dragon, which hunts in groups and, after killing a prey, the largest specimens jumped on it and left the remains for the smallest. . In the process, it is not uncommon for one of the dragons to sustain serious injuries. And the same goes for crocodiles. For Padian, the same scene could have played out with T. rex and other families of tyrannosaurs millions of years ago.
However, Padian himself admits that it will never be possible to test his hypotheses, although he could find a correlation if he examined all the T. rex specimens in museums around the world for bite marks. "Bite wounds to the skull and other parts of the skeleton -he explains- are well known in other tyrannosaurs and carnivorous dinosaurs. If he finds fewer bite marks on the shrunken limbs, it could be a sign that the shrunken is limited in size.”
