NEW YORK (AP) _ An amateur fossil hunter has discovered what may be the biggest meat-eating dinosaur known, a fearsome beast that looked like the longtime record-holder Tyrannosaurus rex.

The creature was 41 to 43 feet long and weighed 6 to 8 tons when it roamed the grasslands of what is now Argentina, scientists estimate.

It lived about 100 million years ago, or about 30 million years before T. rex appeared, said paleontologist Rodolfo Coria of the Carmen Funes Museum in Neuquen, Argentina.

A bone-by-bone comparison with remains of the largest known specimen of T. rex suggests that the newfound creature was slightly longer and maybe three tons heavier, said Coria, who reported the fossil find with an Argentine colleague in Thursday's issue of the journal Nature.

``This is a monstrous animal,'' said University of Chicago paleontologist Paul Sereno, who has examined the newfound fossils. ``It's probably a bit bigger than T. rex.''

Scientists are uncertain how big T. rex got. Estimates range from about 40 feet to 50 feet.

The initial fossil find was made by a local auto mechanic who hunts dinosaur bones as a hobby. In honor of the discoverer, Ruben Carolini, the huge dinosaur has been named Giganotosaurus carolinii.

Scientists have recovered about 70 percent of the skeleton, including parts of the 5-foot-long skull, most of the vertebrae, both thigh bones and curved, serrated teeth about 8 inches long. Without a complete skeleton scientists can only estimate the creature's size.

The creature ran on its hind legs and probably had rather small arms, Coria said in a telephone interview. Just what it ate in its environment, which resembled the African savanna, is a mystery, he said.

Despite the overall similarity in appearance to T. rex, Giganotosaurus was not closely related to it, and the two beasts arose independently, Coria said.

T. rex lived in North America, and there was no land bridge from South America that could have let Giganotosaurus or its descendants move north to become ancestors of T. rex, Sereno said.

Jack Horner, curator of paleontology at the Musem of the Rockies in Bozeman, Mont., said comparing the sizes of Giganotosaurus and T. rex is tricky because dinosaurs grew continuously until they died, rather than stopping at some adult length.

``I don't care who's bigger. That's not the interesting question,'' he said.

More important will be finding out whether Giganotosaurus was a hunter or a scavenger, he said. T. rex is usually considered a hunter, but Horner has suggested it was a scavenger.

In any case, fossils of a meat-eating dinosaur from North Africa suggest a beast that was bigger than T. rex, he said. No analysis of those bones has been published, he said.