A small predator that hunted in South America 230 million years ago represents one of the earliest-known dinosaurs and foreshadowed later meat-eating beasts like Tyrannosaurus rex, according to scientists from Argentina and the United States.
In findings published on Friday in the journal Science, they described the discovery of a dinosaur called Eodromaeus, meaning "dawn runner."
It was a modest creature -- measuring about 4 feet long and weighing only 10 to 15 pounds (4.5 to 6.8 kg) -- that walked on two legs and possessed a long neck and tail, sharp claws and saber-shaped teeth.
But the scientists said it paved the way for some true monsters like T. rex. Tyrannosaurus, which lived at the very end of the age of dinosaurs 65 million years ago, approached 50 feet in length and weighed about 6 tonnes.
The scientists found the fossilized remains of Eodromaeus in Argentina's "Valley of the Moon," a region that has provided a glimpse into some of the earliest days of the dinosaurs during the Triassic period.
"The dawn of the age of dinosaurs is coming into focus," Argentine paleontologist Ricardo Martinez, one of the scientists, said in a statement.
Eodromaeus was very close to the root of the dinosaur family tree, but already boasted features typical of the later meat-eating dinosaurs.
"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," University of Chicago paleontologist Paul Sereno, who also took part in the study, said in a statement.
"Who could foretell what evolution had in store for the descendants of this pint-sized, fleet-footed predator?" Sereno added.
Two near-complete skeletons were found side-by-side in 1996 in a desert area in western Argentina, but scientists had to study the fossils thoroughly to determine that they belonged to a previously unknown dinosaur.
The scientists said Eodromaeus lived alongside another very early dinosaur called Eoraptor, a similar-sized creature that ate plants whose descendants eventually would include giant, long-necked sauropod dinosaurs like Apatosaurus and the truly gargantuan Argentinosaurus.
Eodromaeus, with its stabbing canine teeth and sharp-clawed grasping hands, was a precursor to the dinosaur meat-eaters called theropods, like T. rex, Allosaurus and Giganotosaurus, as well as to birds, the scientists said.