Scientists discover dinosaur that had arms like a T Rex

A new kind of dinosaur has the same type of small arms as a T-Rex, and it's giving researchers a better idea of how these types of arms developed. 

The new dino is called the Gualicho shinyae, according to a new study out Wednesday. It's considered an allosaurid, meaning that it's a medium-sized carnivorous dinosaur. It was only 6 feet tall up to the hips, which means it wouldn't be considered large compared to a T-Rex.

Surprisingly, the researchers found, the Gualicho shinyae had short arms, the length of a child's arms. Plus, its hands only had two fingers, which was also similar to the T-Rex. This wasn't something they were expecting, especially because the Gualicho shinyae fell under a different branch of the dinosaur family tree than the T-Rex.

That means that the shorter arms were a trait that developed independently of some shared short-arm predecessor. It's something called "convergent evolution," which means that two unrelated organisms developed similar characteristics.

Ever since the T-Rex was discovered in the early 1900s, researchers have been trying to figure out what caused the T-Rex to develop such short arms, according to Pete Makovicky, one of the authors of the new study and the curator of dinosaurs at the Field Museum. At first, it seemed like it might be part of some shared lineage, but the Gualicho shinyae threw a wrench in that idea.

"It's telling us that there's some adaptive advantage to the small arms," he said. "Insights into the 'how' it happened will get us closer to 'why.'"