Why did the T. Rex have short arms? A new dinosaur revives the debate

It’s a question that’s haunted people ever since the first Tyrannosaurus rex fossils were discovered: why did the terrifying predator have those crazy short front legs? Paleontologists have discovered a new species of dinosaur in Argentina that looks a lot like T. rex, including clumsy arms, and they also have an idea why they were so small.

Its forelimbs were so short that when the first skeletons of T. rexen were discovered around 1900, researchers could barely imagine these mini-limbs belonged to the enormous beast. “They were from a different beast, they first thought,” says paleontologist Melanie Pendant, who is currently doing doctoral research at Uppsala University in Sweden. “Understandable. They are also very short.”

Nevertheless, the mini legs were indeed part of the prehistoric carnivore. In fact, later more species were found with even shorter arms. But an explanation? In fact, more than a century later, we still don’t know.

With the discovery of another dino with unimpressive limbs, this time in Patagonia, the question is once again very much in the news, and it is once again being talked about a lot.

Over the years, many theories have been floated around the world. One of the most popular is that the legs were only used when mating. During can imagine anything. “The tail got in the way when mating, so they were able to use some extra support.”

Another idea is that the arms are an evolutionary residue that stuck to T. rex as a sort of appendage. Quite possible, according to the researcher, because in some birds that no longer really fly, we also see shorter wings.

And last month, based on several studies, scientists proposed the theory that the legs were short enough to ensure that they were not accidentally torn off by a fellow creature. This could happen if the beasts hunted in groups and dived together for prey, such as crocodiles and alligators.

But that’s not how evolution works, notes paleontologist Pendant. “Evolution doesn’t think about the future, I think it’s beneficial, so let’s shorten the legs a bit. There’s a book on evolution called The blind watchmaker. That’s evolution: super complex but without any idea or planning.”

And then there’s this new dino: the Meraxes gigas (“Meraxes” is a dragon of game of thrones, ‘gigas’ speaks for itself, with a head to tail length of more than 10 meters). It looked like T. rex but was unrelated. The noticeable deformations of the animal’s skull may have been an ornament to attract mates. And those short arms too.

The scientists who describe the new species in the professional journal Current biology leaning towards a new theory: the energy that went to the front limbs in other species, in the Meraxes gigas – and the T. rex – went to another part of the body: the enormous skull.

It is also a plausible explanation, according to the paleontologist. “But those other theories might as well be true. In fact, they’re not even mutually exclusive. They really did do something with those arms, because the bones are pretty sturdy, just really small. But what exactly, you can only do that about speculation. Which is actually much nicer: that they found and described a new species of dinosaur.