OSLO - A giant fossil sea monster found in the Arctic and known as Predator X had a bite that would make T-Rex look feeble, scientists said on Monday.

The 15-metre-long Jurassic era marine reptile had a crushing 15 tonnes per square inch bite force, the Natural History Museum of Oslo University said of the new find on the Norwegian Arctic archipelago of Svalbard.

"With a skull that's more than 10 feet (3 metres) long you'd expect the bite to be powerful but this is off the scale," said Joern Hurum, an associate professor of vertebrate paleontology at the museum who led the international excavation in 2008.

"It's much more powerful than T-Rex," he said of the pliosaur reptile that would have been a top marine predator. Tyrannosaurus Rex was a top land carnivore among dinosaurs.

The scientists reconstructed the predator's head and estimated the force by comparing it with the similarly-shaped jaws of alligators in a park in Florida.

"The calculation is one of the largest bite forces ever calculated for any creature," the Museum said of the bite, estimated with the help of evolutionary biologist Greg Erickson from Florida State University.

Predator X's bite was more than 10 times more powerful than any modern animal and four times the bite of a T-Rex, it said of the fossil, reckoned at 147 million years old. Alligators, crocodiles and sharks all now have fearsome bites.

The teeth of the pliosaur, belonging to a new species, were a foot (30 cms) long. The scientists reconstructed the reptile from a partial skull and 20,000 fragments of skeleton.

The pliosaur, estimated to have weighed 45 tonnes, was similar to but had more massive bones than another fossil sea monster found on Svalbard in 2007, also estimated at 50 feet long and the largest pliosaur to date.

"It's not complete enough to say it's really bigger than 15 metres," Hurum said of the new fossil.

Hurum had said of the first fossil pliosaur that it was big enough to chomp on a small car. He said the bite estimates for the latest fossil forced a rethink.

"This one is more like it could crush a Hummer," he said. referring to General Motors' large sport utility vehicle.

Among other findings were that the pliosaur had a small thin brain shaped like that of a great white shark, according to scans by Patrick Druckenmiller of the University of Alaska.

Pliosaurs preyed upon squid-like animals, fish, and other marine reptiles. Predator X had four huge flippers to propel itself along, perhaps using just two at cruising speeds and the others for a burst of speed.