Dog-sized ancestor of mighty T rex unearthed

Tyrannosaurus rex had a pint-sized skinny ancestor that lived when dinosaurs were the underdogs 230 million years ago, scientists have discovered.

Eodromaeus was only 4ft long from nose to tail-tip and weighed a mere 10-15lb.

But the two-legged dinosaur gave rise to the biggest and most ferocious land predators that have ever lived, including T rex.

In a rare find, fossil bones of two of the creatures were unearthed side-by-side at a desert site known as the Valley of the Moon in northern Argentina.

Study leader Dr Paul Sereno, of the University of Chicago, US, said: "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.

"Who could foretell what evolution had in store for the descendants of this pint-sized, fleet-footed predator?"

The site where Eodromaeus was found, in the foothills of the Andes, has already yielded clues about the early origins of the dinosaurs. In 1991 Dr Sereno found another species called Eoraptor. About the same size as Eodromaeus, its descendants would include the giant long-necked sauropods such as Diplodocus.