A marine monster described as the most fearsome animal ever to swim in the oceans boasted a bite up to 11 times as strong as that of Tyrannosaurus rex.

The fossil remains of the huge pliosaur were dug up last summer from the permafrost on Svalbard, a Norwegian island close to the North Pole.

Analysis revealed that it was a turbo-charged swimmer. Its front flippers allowed the creature, dubbed Predator X, to cruise along comfortably but when prey came into range the power of its hind flippers kicked in to provide extra acceleration.

Measurements of its jaw and the killing power of its dagger-like teeth have shown that it could bite down with a force of 33,000lb per square inch compared with T. rex’s 3,000lb per square inch. Alligators have the strongest bite today with about 2,500lb per square inch.

Researchers have been astonished by the size of the reptile, which exceeded even that of another pliosaur, called The Monster, which was found at the same site a year earlier.

Predator X is thought to have been at least 50 feet long, perhaps more, and measurements of its bulk suggest that it would have weighed in at 45 tonnes.

Its discovery was announced yesterday in Oslo by Jørn Hurum, of the University of Oslo, who led the expedition to dig up the remains. At least 20,000 fragments have been recovered including most of the jaws, which were 10 feet long. Dr Hurum said: “It was the most ferocious hunter ever. It’s like a turbo-charged predator. This is a very, very large carnivore.”

He added that Predator X was smaller than the biggest marine reptile yet known, a 75ft ichthyosaur from 210 million years ago, and was about the same length as the largest fossil shark to have been identified by palaeontologists. Predator X, however, was armed with much bigger teeth and, with its ability to close in at enormous speed, would have been much faster and deadlier than either of them.

Dr Hurum believes that Predator X and The Monster are likely to represent the same species of pliosaur. “Its anatomy, physiology and hunting strategy all point to it being the ultimate predator — the most dangerous creature to patrol the Earth’s oceans.”

The turbo-charge feature of its hind flippers was identified in tests by John Long, of Vassar College, New York State, using a four-flippered robot called Madeline.

Researchers had been puzzled about why the marine predator should have needed four flippers when the front two were perfectly adequate for it to swim well.

A CT scan of a pliosaur skull held at the Natural History Museum in London has showed that the ancient marine predators had a brain the same shape and proportion as the great white shark, which is regarded as today’s “perfect killing machine”.

Times Recommends

• Times Christmas appeal: Letter from the Editor
• Conferences — what a waste of money
• Schools supremo learns a painful lesson