A dino king's ancestor.

Tyrannosaurus rex gets a lot of attention for being one of the fiercest large dinosaurs that ever lived. These fearsome meat eaters, however, weren't the first of their kind.

In northwestern China, paleontologists have found remains of Guanlong wucaii, the oldest known dinosaur that belongs to the tyrannosaur family. The name means "crowned dragon from the five-colored rocks," and the species lived about 160 million years ago.

G. wucaii were only 3 meters (9.8 feet) long, but they were probably ancestors of the much larger T. rex, which lived 95 million years later, researchers say.

In China, the researchers found two G. wucaii skeletons that were nearly complete. One appeared to be a 12-year-old adult. The other was a 6-year-old youngster. Each one had a hollow, bony crest running along the top of its snout.

The crest, which was 6 centimeters (2.4 inches) tall on the adult (and smaller on the juvenile), baffles scientists. The crest wasn't connected to the creature's nose. Nor did it appear to be useful for fighting. Instead, it's possible that the structure served as a sign of adulthood or a way for the animals to tell the difference between males and females. It could have also helped them recognize members of their own species.

The new fossils shed light on debates about tyrannosaur evolution. Paleontologists used to think that T. rex and its cousins evolved from huge predators that lived 145 million years ago. Now, it appears that tyrannosaurs evolved much earlier than that, from a group of small, meat-eating dinos called coelurosaurs.