What may be the earliest known relative of T. rex and all meat-eating dinosaurs has been discovered. The dog-sized mini-predator would've made its future relatives proud as it fed on small dinosaurs and the young of other reptiles, and is now shaking up what scientists had previously learned about the evolution of those extinct giants.

The small, lanky, two-legged carnivore named Eodromaeus murphi - Eodromaeus being Greek for "dawn runner," murphi in honor of field volunteer Jim Murphy - weighed only 10 to 15 pounds (4.5 to 6.8 kilograms) and measured about 4 feet (1.2 meters) in length from snout to tail. The skeletons of two specimens were discovered side-by-side in 230-million-year-old iron-rich stone in the "Valley of the Moon" at the foothills of the Andes in northeastern Argentina, which was once the southwest corner of the supercontinent Pangaea.

"With a hike across the valley, you literally walk over the graveyard of the earliest dinosaurs to a time when they ultimately dominate," said researcher Ricardo Martinez, a paleontologist at the National University of San Juan in Argentina.

Dino graveyard

The predator came from the dawn of the age of dinosaurs, a time we know relatively little about. The long-necked, long-tailed predator was armed with saber-shaped upper cheek teeth and sharp-clawed five-fingered hands. [Images: Dinosaur Fossils]

"Seeing what a modest beginning this lineage had, no one would have ever thought it would evolve to giant predators like T. rex," researcher Paul Sereno, a paleontologist at the University of Chicago, told LiveScience.

Sereno, Martinez and their colleagues concluded Eodromaeus was likely a very close relative of the ancestor of the theropod lineage, which includes all predatory dinosaurs. Key features it had in common with theropods include long finger bones tipped with claws that enhance grasping, and pockets in the sides of the neck vertebrae for air sacs from the lungs. [Image of Eodromaeus' tiny skull]

"It really is the earliest look we have at the long line of meat eaters that would ultimately culminate in Tyrannosaurus rex near the end of the dinosaur era," Sereno said. "Who could foretell what evolution had in store for the descendants of this pint-sized, fleet-footed predator?"