Norwegian researchers found the skeletons of 28 reptiles - including a rare predator described as the "Tyrannosaurus Rex of the oceans" - in the Svalbard archipelago north of Norway.
"We were not in Svalbard to excavate any skeletons. We were there to map skeletons to find one place where we could do a big scientific expedition in the next years, and we really found the treasure trove for that," Joern Hurum, an assistant professor at the University of Oslo, said.
The skeletons were discovered in August, partially sticking out of the Jurassic-era rocks, on the island of Spitsbergen, about 1,000km from the North Pole.
"One of them was this gigantic monster, with vertebrae the size of dinner plates and teeth the size of cucumbers," Hurum said.
Scientists hope to find a complete skeleton of the plesiosaur when they return to the area next summer but for now they have returned to Oslo to reconstruct the crumbled skull they unearthed.
"It's like a sea lion with a crocodile skull in the front but it's a 10 metre sea lion, the size of a bus," Hurum said.
The fossil graveyard is about
1,000km south of the North Pole
The bones of 21 plesiosaurs, a long-necked reptile esembling a cross between a tortoise and a snake, and six ichthyosaurs, giant reptiles that look like dolphins, were also found.
Plesiosaurs, which swam with two sets of flippers, often preyed the smaller ichthyosaurs but all became extinct when the dinosaurs vanished 65 million years ago.
The scientists rated the fossil graveyard "one of the most important new sites for marine reptiles to have been discovered in the last several decades".
"It is rare to find so many fossils in the same place - carcasses are food for other animals and usually get torn apart," Hurum said.
Hurum said he believed the reptiles had died over thousands of years and become preserved in a deep layer of black mud on the seabed.
He added that the presence of fossils was also an interesting sign for geologists hunting for oil and gas deposits in the Barents Sea to the east. "A skull we found even smells of petrol," he said.