llustration by Todd Marshall via Science

Meet Raptorex kriegsteini, a new dinosaur species described this week in the journal Science. This “tiny” Tyrannosaurus rex ancestor would still look big to us at nine feet (three meters) tall., but quite small compared to its descendent T. rex. Other than the size difference, the two dinosaurs look remarkably alike, according to Paul Sereno of the University of Chicago and a National Geographic Explorer-in-Residence.

This new dino changes the way scientists think about the evolution of T. rex‘s short arms. Raptorex kriegsteini also had short arms, meaning that T. rex‘s short arms evolved later than previously believed, according to Thomas Holtz of the University of Maryland (who is not associated with the study).

Learn more about this find on National Geographic News.

Get the facts on Tyrannosaurus rex on National Geographic Kids.

Search for T. rex bones in Zipper’s Cave Maze.

Learn
more about paleontologist and National Geographic Explorer-in-Residence
Paul Sereno on National Geographic.