Real sea monsters: The hunt for predator X

EACH summer, a team from the University of Oslo in Norway go hunting for monsters on the island of Spitsbergen. They carry guns in case they get menaced by the world's largest living land carnivore, the polar bear. But it is not bears they are after. They are searching for much bigger quarry, the most formidable predators that ever lived.

Step back 150 million years and Spitsbergen was covered by a cool, shallow sea swarming with marine reptiles. The creatures died out and their fossils became part of an island stuffed full of bones. Nowhere else in the world are so many marine reptiles found in one place.

For a few short weeks the sun never sets and temperatures soar to just above freezing. Knowing that before long the ground will be frozen solid, the researchers dig like crazy. "It's like a gold rush, there are so many fossils waiting to be found," says team leader Jørn Hurum. "The site is densely packed with skeletons. As we speak there are probably more than 1000 skeletons weathering out."

Hurum's Arctic discoveries are part of a remarkable renaissance in interest in the marine reptiles of the Mesozoic era, 251 to 65 million years ago – including this week's announcement of a colossal new marine reptile from the "Jurassic coast" of Dorset in southern England. We now know more about this group of creatures than ever before.

Marine reptiles were among the first vertebrate fossils known to science and were key to the development of the theory of evolution. In the late 18th century the massive jaws of a lizard-like beast were found in a mine in Maastricht in the Netherlands. Later named Mosasaurus, the creature helped convince scientists that animals could become extinct, a radical concept in its day. In the early 19th century, ichthyosaurs and plesiosaurs discovered by legendary fossil hunter Mary Anning around Lyme Bay in south-west England helped establish the science of palaeontology. Marine reptiles were among the best-understood extinct creatures of the first half of the 19th century and played a major role in the intellectual debate nurturing Darwin's theory of evolution.

Yet they faded from view as their terrestrial relatives moved to centre stage. It took nearly a century for marine reptile research to emerge from the shadow cast by the dinosaurs. "Scientists thought they knew all there was to know," says plesiosaur expert Leslie Noè of the Thinktank museum in Birmingham, UK. "The idea was that they weren't worth studying. Nobody would say that now. Our understanding of marine reptiles is phenomenally greater now than it was even 10 years ago."

In the modern world, marine reptiles are few and far between: saltwater crocodiles, turtles and sea snakes are rarities of coastal waters. However, in the ice-free greenhouse of the Mesozoic, reptiles cruised the oceans from pole to pole, occupying the ecological roles now largely filled by whales, dolphins, porpoises, seals and even sharks.