A team of leading paleontologists announced on Monday the discovery of what may be one of the largest meat-eating dinosaurs known to have stalked the earth, after finding hundreds of bones in sandstone 100 million years old.
The remains of the creature, Mapusaurus roseae, were unearthed in a quarry in Patagonia, Argentina, with measurements suggesting full-grown adults weighed an estimated eight tons and exceeded a length of 12.5 metres, longer than any yet found from their "cousins" the Tyrannosaurus rex.
While the dinosaur is believed to have stood taller, it bore a resemblance to the Tyrannosaurus as a two-legged carnivore with an enormous head, stubby arms and large powerful jaws.
"Over the last decade, people have become increasingly aware of a group of gigantic meat-eating dinosaurs called carcharodontosaurids," said Dr. Philip Currie of the University of Alberta, who co-led the excavation with Professor Rodolfo Coria, of Argentina's Museo Carmen Funes.
"These animals include Giganotosaurus, which was larger than the largest known specimen of Tyrannosaurus rex," he said in a written statement.
After some five years of working in the dinosaur quarry, the team discovered a new species of carcharodontosaurid that they called Mapusaurus roseae.
The remains include what may be one of the biggest meat-eating dinosaurs known, slightly larger than its older cousin, Giganotosaurus.
The discovery, made nearly 25 kilometres south of the city of Plaza Huincul in 1995, took an estimated five years of excavation under the direction of Coria and Currie who removed 100 tons of sandstone from a desert hilltop.
When the bones were first found some 10 years ago, scientists believed they were dealing with the skeleton of one very large animal.
But after several months, Currie said, it became evident that the bones belonged to at least seven individuals from a new species.
The close grouping of the bones suggests the hunters stalked their prey in groups, which would have given the Mapusaurus an advantage in felling even huge beasts such as the plant-eating Argentinosaurus, which had an estimated weight of 100 tons.
The Argentinosaurus, the largest dinosaur that ever lived, shared its habitat with the Mapusaurus in Argentina some 100 million years ago.
"So picture this, instead of a single Tyrannosaurus rex chasing you, or a single Mapusaurus chasing you, you've got half a dozen to a dozen of these things at you all at once -- and start thinking of your chances of survival on that one," Currie told CTV News.
The individual Mapusaurus dinosaurs found ranged in size from juveniles at 5.5 metres long to a robust adult that exceeded 12.5 metres in length, the paleontologists said.
The excavation of the quarry was partly sponsored by dinosaur expert Don Lessem, who set up two charities, the Dinosaur Society and the Jurassic Foundation, to fund such work. He was also an adviser to the film Jurassic Park.
At the time, the film was criticized by some paleontologists as being unrealistic for depicting predatory dinosaurs hunting in a pack.
"This is fresh information about the social lives of the largest carnivores on Earth. And its one of the most remarkable of a dozen new species discoveries, many of them gigantic, in the last decade from this region of western Patagonia," said Lessem.
Mapusaurus is named for the word "earth" in the language of the Mapuches, the Native American tribe of western Patagonia. Its species name "roseae" refers to the rose-coloured rocks that the specimens were found in and also honours the first name of the Argentina-Canada Dinosaur Project's main donor.
The Argentina-Canada Dinosaur Project was initiated in 1997 by Argentina's Museo Carmen Funes and the Royal Tyrrell Museum of Palaeontology, which is found in Drumheller, Alta.
While the excavation has answered some questions, the investigation is far from over.
The dinosaurs are believed to have been living together in a pack when they died.
"We still don't know, for example, what killed these animals all at once -- and that's intriguing," Currie said.