for National Geographic News
Skeletons of a huge, meat-eating dinosaur that overshadows Tyrannosaurus rex have been discovered in Argentina.
The newly revealed species is one of the biggest carnivores ever to have walked the Earth, dinosaur experts say.
At least seven of the animals were uncovered together in a mass fossil graveyard in western Patagonia, a region famous for giant-dinosaur remains.
Living some 100 million years ago, the largest specimen was more than 40 feet (12.5 meters) long.
Researchers say the new species, named Mapusaurus roseae, is possibly even larger than its close relative Giganotosaurus, which in 1995 took T. rex's crown as the world's biggest known carnivorous dinosaur.
The find is also one of the first to suggest giant meat-eating dinosaurs lived in groups.
Renowned dinosaur hunter Rodolfo Coria, professor at the Carmen Funes Museum in Plaza Huincul, Argentina, found the fossils in the foothills of the Andes mountains.
Coria and fellow paleontologist Philip Currie of the University of Alberta in Canada describe the find in the latest issue of the journal Geodiversitas.
While more than matching T. rex for size, Mapusaurus appears to have been a sleeker, more agile predator, with teeth designed for slicing flesh rather than crushing bones.
Coria says the new dinosaur's skull is longer than T. rex's.
"The lower jaw is also more delicate in Mapusaurus, and its teeth are thinner and sharperthey are just like knives," he added.
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