Newly identified T. rex ancestor is "missing link" between apex predators, dinosaur researchers say

More than 85 million years ago, a smaller-bodied ancestor of the Tyrannosaurus rex roamed the plains of Mongolia. The dinosaur's identity was unknown — until now.

In a study published Wednesday in Nature, scientists describe the identification of a new tyrannosauroid named Khankhuuluu mongoliensis. Apex predators, including the T. rex, eventually arose from these smaller-bodied tyrannosauroids, the study's researchers said.

"This species, Khankhuuluu, is the missing link between smaller and earlier forms and the larger apex predatory tyrannosaurs," paleontologist Darla Zelenitsky, a professor at the University of Calgary and study co-author, told CBS News.