OOKING up at the 46-foot-long skeleton of the long-extinct marine monster that is hanging up in the lobby of the Bermuda Underwater Exploration Institute, it's hard to believe that such a creature ever existed on this planet.

The odd-looking Elasmosaurus, with its bizarrely long neck and small head, is just one of a host of ancient creatures that will be gracing the BUEI over the next five months in the Savage Ancient Seas exhibition, which opens on June 4.

Others include the "pitbull of the sea", a 17-foot giant of a fish with teeth like those of a lion, a predator that swallowed its prey head first.

And if you think that sounds nasty, you should see the eight-foot-high jaws of a massive prehistoric shark, complete with colossal, razor-sharp teeth, from a creature that grew to the size of three buses and whose diet included whales.

Even the molluscs were massive.

Supervising the assembly of the giant fossils this week was David Ehlert, director of the Rocky Mountain Dinosaur Resource Centre (RMDRC) in Colorado, which has loaned out the monsters.

Asked why so many life forms were enormous in the prehistoric age, palaeontologist Mr. Ehlert gave his opinion.

"Competition for food is the most likely source of giganticism," Mr. Ehlert said. "When the dinosaurs were around, about midway through their time they were extremely large, with many of them 60 to 120 feet long.

"At that point, there was no competition for food. Some of these huge creatures could reach 70 feet up to eat the tree tops. They were only competing with each other."

While the names and appearance of many on-land dinosaurs are widely familiar, the same does not apply to their marine contemporaries. But they were unimaginably huge as well.

The fossils of the creatures on display at the BUEI were recovered from various sites in Kansas. But how did areas that are just about as far in-land as it is possible to get turn out to be a rich source of marine fossils?

"In the US, between 80 and 90 million years ago, there was an interior seaway, only about 600 feet deep," Mr. Ehlert explained.

"It was tropical and the creatures that lived in it had a bountiful supply of food to prey upon.

"If you make a comparison with creatures of today, look at the blue whale, the largest living mammal, which grows to around 80 or 100 feet. The whole of that animal is made up of krill, tiny shrimp, that it's been eating all its life.

"If you look at the prehistoric predators, they ate fish like a blue whale eats krill. All we see is the bones, you have to imagine how big their bodies were."

Mr. Ehlert has been involved in digging up some of the marine fossils that are on display at his museum in Colorado and he explained the meticulous effort the task requires.

"It's not like the way of discovering a fossil ? you find one bone, keep digging and you find the entire animal laid out neatly in the ground, while champagne corks are popping," Mr. Ehlert said.

"Particularly with sea creatures, you find remains that have been completely flattened under rocks. So what you find is a two-dimensional image.

"What we have to do is to take out the bones, one by one, and make a copy of each in plastic. Then we can bend the plastic and create a three-dimensional version.

"Dinosaur bones seem to stand up better, but marine creatures have thinner bones and they get completely squashed.

"The truth is that it's almost impossible to find a complete animal. What we're realistically looking for is about 50 per cent of an animal.

"From that amount, generally we can reconstruct the rest, working from other examples that have been found. Quite often two specimens of the same species are combined to create a complete skeleton."

Visitors to the BUEI, through October 22, will be greeted by the spectacular suspended skeleton of the long-necked Elasmosaurus, bathed in fiery orange light, against the backdrop of an erupting ancient volcano.

Clever use of lighting means there are some eerie shadows of skulls and bones thrown onto the walls, adding to the general scariness of the monsters on display.

Given a prime spot, suspended above the Institute's stairway, will be the savage Xiphanctinus, a barrel-chested beast of a fish with a face straight from a nightmare. With massive teeth, built for puncturing and grasping, this 17-foot monster would have eaten almost anything that swam, including smaller predators.

There are also a couple of examples of Clidastes, a marine lizard of between eight and 20 feet in length and also a predator. The most remarkable thing about this species was its dental characteristics ? it had two sets of teeth.

The secondary set was at the back of the mouth and enabled the lizard to lock squirming prey in place.

The creature was a mosasaur and the BUEI will also be displaying the 6ft skull of the largest of the species ever found. This lizard, known as Tylosaurus, has banana-sized front teeth backed up by its inner teeth. It could flex its lower jaw in the manner of a snake, allowing it to swallow even large prey whole.

The Institute was so impressed by the skull, it decided to buy a plastic resin cast copy of it to keep as a permanent exhibit.

The jaws of the giant shark ? Carcharodon Megalodon ? will form the frame of many photographs of visitors taken over the coming months.

The jaws come from a specimen, discovered in Florida, that was 50 feet in length and 50 tons in weight. It dates back to more recent times than the other marine monsters ? about 20 million years back ? and it became extinct a mere 1.5 million years ago.

exhibit, a Coelacanth modelled on a fossil dating back at least 65 million years, is a fish that still exists. It has been around since before the time of the dinosaurs and has proved to be one of the greatest survivors in Earth's natural history.

It was thought to be extinct until one was caught in 1938. Since then, live Coelacanths have been caught off Madagascar.

"The case of the Coelacanth shows that there is much more to be discovered in the sea," said BUEI director Wendy Tucker. "There is a huge ocean out there and we only know about a fraction of it."

For Ms Tucker, the Savage Ancient Seas exhibition is part of a new trend that she hoped would keep the BUEI experience fresh.

"This is the first time we've brought a travelling exhibit and it's something we hope to do again," Ms Tucker said.

"People sometimes say we need to change our displays, but it's very expensive to change a permanent exhibit.

"We try to keep the BUEI attractive for people to visit and revisit and using travelling exhibits is one way we can do that."

She pointed out that the Institute was constantly adding to its displays. One notable addition is the skull and tusk of a Narwhal, an Arctic whale.

The left tooth of the male Narwhal grows to up to 10 feet long and is marked by a spiral pattern, similar to that of the tusk of the legendary unicorn.

Scientists believe that the dinosaurs and their marine cousins were wiped out by the effects of an asteroid that collided with Earth some 65 million years ago.

The nine-mile-wide rock smashed into Mexico's Yucatan Peninsula and kicked up a cloud of debris that blocked out sunlight, causing temperatures to plunge and vegetation to die.

So don't worry ? there's no chance that a Xiphactinus will sink its considerable teeth into your leg when you next go for a dip.