The remains of a bus-sized prehistoric sea reptile found on a remote Arctic island may be an entirely new species, researchers said Tuesday.

Initial excavation of a site on the Svalbard islands, 300 miles north of Norway's mainland, in August yielded the remains — teeth, skull fragments and vertebrae of a reptile estimated to measure over 12 metres long, said Joern Harald Hurum of the University of Oslo.

"It seems the monster is a new species," he told the Associated Press.

The reptile appears be the same species as another sea predator whose remains were found nearby on Svalbard last year. His team described those 150-million-year-old remains as belonging to a short-necked plesiosaur measuring more than nine metres, "as long as a bus … with teeth larger than cucumbers."

The short-necked plesiosaur was a voracious reptile often characterized as the Tyrannosaurus rex of the oceans.

Mark Evans, a plesiosaur expert at the Leicester City Museums in Britain, said he did not know enough about the Norwegian find to comment on it specifically. But he said new types of the sea reptiles are being found.

"We are regularly seeing new species of plesiosaurs popping up — in a way because, in the past 10 or 15 years, there has been what we call a renaissance in plesiosaur research," Evans said by telephone.

Hurum said the team had only managed to excavate a three-metre area of the find. The Norwegian-led team plans to present more detailed findings early next year, and will return to Svalbard to excavate further next year.