About 100 million years ago, a giant predatory dinosaur stalked what is now the Patagonian region of Argentina. Weighing more than four tons and stretching about 36 feet long, the newly discovered carnivore shared several physical traits with Tyrannosaurus rex, including an enormous head and tiny front arms
But the new species, described today in a study published in the journal Current Biology, is not closely related to tyrannosaurs. It belonged to a totally different group of dinosaurs known as the carcharodontosaurids, and it went extinct millions of years before T. rex appeared on the scene. It therefore evolved its tiny arms independently, suggesting that having little forelimbs may have had more evolutionary advantages than previously thought.
“I’m convinced that those proportionally tiny arms had some sort of function,” the new study’s lead author, paleontologist Juan Canale of the National University of Río Negro in Argentina, said in a press release. “They may have used the arms for reproductive behavior such as holding the female during mating or support themselves to stand back up after a break or a fall.”