Biggest killer dinosaurs unearthed in Patagonia

Palaeontologists working in Patagonia have tracked down the biggest flesh-eater ever to walk the Earth, finally confirming theories put forward by the late novelist Bruce Chatwin about the lives and stomping grounds of dinosaurs.

Almost 20 years ago, in his book In Patagonia, Chatwin described how his obsession with a scrap of skin compelled him to track down the cave of a prehistoric giant sloth - the glyptodon. The tale of this personal quest in a remote landscape was to spur a scientific monster hunt throughout Argentina's southern badlands, east of the Andes. The place turned out to be cluttered with the ancient bones of prehistoric giants, like some Jurassic memorial park.

In the 10 years since Chatwin's death, the fossil boneyards beneath Patagonia's arid dunes have yielded rich finds, and professional fossil-hunters go to great lengths to gather more. The latest discoveries, announced this week, alter academic theories of dinosaur behaviour.

Long before there were gauchos, pampas, or even Andes mountains, huge herds of saurian beasts rumbled across a lush Patagonia. Huge is the key word here: investigation of six partial skeletons unearthed by a team of Argentine and Canadian palaeontologists reveals that dagger-toothed dinosaurs, five feet longer than Tyrannosaurus rex, may have formed into packs to stalk reptilian prey even more immense.

Everywhere else, carnivorous dinosaurs have been identified as solitary hunters. But in Patagonia, theevidence points to plant-eating dinosaurs that grew so big that only co-operative, pack-hunting tactics, similar to those of wolves, could bring them down.

Next month, helicopters will help haul out the neck vertebrae - each nearly four foot across - of another newly identified dinosaur species. The Rio Negro giant, a 160ft-long swamp-dwelling creature bigger than any other, was excavated in January from a desolate Patagonian grazing spot called La Buitrera (the buzzard cage).

Although huge, the Rio Negro giant had a tiny head on a serpentine neck. Stretching up to nibble fruits, it would have looked like the Loch Ness monster of legend on steroids, as large as a five-storey building.

Carlos Munoz, an Argentine paleontologist who took part in the dig, believes these creatures moved in herds, like elephants, and defended themselves by lashing out with their powerful tails. They were trailed by small packs of fierce predators, each 50 times larger than a cow.

Last week, Dr Philip Currie of the Royal Tyrrel Museum in Canada, announced that his team's latest discovery in Patagonia beats all records for carnivore size. The still nameless prehistoric beast - 45ft from snout to tail, weighing nearly nine tons - appears closely related to the gigantosaurus, an outsized meat-eating cousin discovered in 1993 in the same area, 640 miles south of Buenos Aires.

"This guy has a long snout, long skull, incredibly sharp teeth - I think it would have been terrifying," Dr Currie said. Last year, he undertook a joint excavation after a goatherd glimpsed what turned out to be 100-million-year-old bones and tipped off Rodolfo Corio, a Patagonian paleontologist, about their location.

Because these bones were found at the same geological level as Argentinosaurus - the world's largest herbivore until the Rio Negro giant was dug up - local scientists assume they were direct links in the food chain. Dr Corio believes the sophisticated communication required to stalk such large prey in packs might also have led the flesh-eaters to practise "patterns of conduct protecting their young".

Dr Corio works at the Carmen Furnes Museum in Neuquen, 50 miles from the Police Hill site where he excavated alongside scientists from the Tyrrel Museum. To finance his digs, Dr Corio won grants from such unlikely sponsors as Universal Studios and Microsoft.

Considering the age of the bones, the pace of discovery in Patagonia is rapid. Last May, a 10-year-old boy stumbled on an 85-million-year-old dinosaur tail while walking his dog in the hills behind his home. Rafael Moyano was scouting for sea shells on the cliffsides for his collection. The fully articulated tail he showed palaeontologists was declared a major find.

A team from Los Angeles found a vast nesting ground nearby, with 300 dinosaur eggs scattered on the side of an extinct volcano. Among them were parts of fossilised embryos, a rare and valuable find, and scraps of fossil dinosaur skin with a complete skeleton. Further south, weather researchers on James Ross Island found deep-frozen bones of a 74-million-year-old dinosaur.

The enormous trophies unearthed in Patagonia have become a source of national pride for Argentines. Marcelo de la Fuente, a paleontologist from La Plata Museum, said: "Africa was the birthplace of man, and our country was the birthplace of dinosaurs."