A University of Chicago researcher is a leader of the team that discovered a small dinosaur that set the stage for giant T. rex.
The quick-moving hunter was 4-foot-long, just 10- to 15-pounds and lived 230 million years ago in what is now South America.
Paul Sereno of the University of Chicago helped with the find.
He says the little dinosaur had a balancing tail and air pockets in the skull, showing it was closely related to Tyrannosaurus rex.
The dinosaur is called Eodromaeus, which means dawn runner.
Sereno is the paleontologist who nearly a year and a half ago discovered another T. rex ancestor, the "Raptorex Kriegsteini," in northern China.