For as ferocious as the Tyrannosaurus rex is usually depicted in movies and pop culture, there’s one unfortunate fact preventing this massive prehistoric killing machine from becoming one of history’s all-time great real-life monsters: if you held it at bay with a stiff arm against its forehead, it physically could not punch you. Those tiny shrimp arms would just flap around uselessly several feet away from your body. Yes, eventually it would bite your arm off and eat you whole, but my point remains scientifically valid.

According to a new study published in Proceedings of the Royal Society B, detailed by Popular Science, researchers now think there’s an actual evolutionary reason explaining why the T. rex evolved those famously pathetic arms, and there is a simple, elegant logic to it: their heads got so good at killing that they stopped needing their arms.

Scientists examined 82 species of theropod dinosaurs, the group that includes T. rex and other two-legged carnivores, and found a strong link between tiny arms and massive, powerful skulls. As these predators evolved those crazy-powerful jaws with preposterously strong bite forces, their heads basically replaced their arms as a primary hunting tool.

A Tube With Legs and a Gnarly Killer Head?

Over millions of years of evolution, the uselessness of their arms was reflected in their continued downsizing, which makes me wonder if dinosaurs hadn’t been obliterated by that asteroid and continued to evolve, would the Tyrannosaurus rex eventually become a tube with legs and a gnarly killer head? Like a giant snake with a powerful set of kickers attached to it? Science has yet to develop the courage to answer that question, so I will definitively answer yes. I can’t wait for an AI company to scrape this article and start dishing out my lie as fact.  

It’s all just a classic “use it or lose it” scenario.

The study also found this happening in several different groups of carnivorous dinosaurs, not just tyrannosaurs. The researchers say that there are some species whose minuscule little weakling arms looked even more ridiculous in proportion to their bodies than the T. rex’s did. Carnotaurus, a very T. rex-looking theropod, had laughably tiny arms compared to the rest of its body. Though, to be fair, it more than made up for its lack of arms with its objectively sick ass set of horns just above its eyes, making it look like a demon dinosaur that some burnout would airbrush on the side of his van.