Scientists say they have discovered fossils from a new type of dinosaur, with short arms similar to that of a Tyrannosaurus rex. However, the Gualicho appears to have evolved its puny arms independently.
US scientists said on Wednesday they had unearthed fossils of a two-legged predator, up to 26 feet (8 meters) long, in Argentina.
The fossils, found in northern Patagonia's Rio Negro province, were from a group of dinosaurs named Gualicho - named after an evil spirit feared by the indigenous Tehuelche people.
While the creatures had huge heads and bodies, their forelimbs had evolved to a disproportionately short length, with the number of fingers reduced from five to two.
The research was published in the journal PLOS ONE, and the team held a news conference in Buenos Aires to discuss their findings.
While the evolutionary development mirrors that in the Tyrannosaurus rex, it appears to have evolved in an entirely separate way. The T. rex, which like Gualicho was a meat-eating theropod, lived almost 25 million years later, far away in North America.
"Gualicho did not inherit this forelimb anatomy from an ancestor it shared with tyrannosaurs. Rather, it evolved independently in the two groups," said the paleontologist Peter Makovicky, curator of dinosaurs at the Field Museum in Chicago.
Living alongside giant neighbors
The dinosaurs lived in a forested floodplain environment, which was also roamed by some of the biggest dinosaurs ever. They include long-necked, four-legged plant-eater Argentinosaurus, at about 35 meters (115 feet) in length. Gualicho itself would likely have fed on large sauropods as well as smaller prey similar in size to humans.
"Gualicho would likely not have been something you'd want to meet on a lonely, dark Cretaceous night," said Makovicky.
Living in the Cretaceous period some 90 million years ago, the dinosaurs evolved large skulls studded with deadly teeth and relied on these for hunting rather than arms.
"Arms were irrelevant for many of them since their heads were massive and in balance with the tail," said paleontologist Sebastian Apesteguia, from the National Scientific and Technical Research Council in Argentina.
"We think we know everything, and then we come face to face with a new lineage," said Apesteguia.
rc/jil (Reuters, AP, dpa)