07/19/2011 04:01 EDT | Updated 09/18/2011 05:12 EDT

Mosasaur Fossils Found In Manitoba: T-Rex Of The Sea

THE CANADIAN PRESS -- WINNIPEG - Manitoba paleontologists have unearthed the bones of several prehistoric sea creatures some 80 million years old, giving them new insight into what Western Canada was like when dinosaurs ruled the Earth.

Scientists from the Canadian Fossil Discovery Centre in southwestern Manitoba have dug up two mosasaurs -- a huge predatory reptile known as the "T. Rex of the sea." The dig site has also uncovered a prehistoric squid and bird skeletons, as well as two other as-of-yet unidentified fossils.

The museum is already home to the largest mosasaur in Canada -- a 13-metre-long creature called "Bruce" -- but curator Anita Janzic said the new find is significant. The discovery of some shore bird fossils seems to suggest there was a lot more available land at a time when much of the Prairies was under salt water.

"It was not just this big, wide, open sea," she said. "It's giving us some new insight into what the seaway was like -- a more shallow marine than some of the other places are thought to be. That is changing how we are looking at the seaway and that, to me, makes this site very interesting."

Despite being about as far from the ocean as you can get, some of Canada's richest deposits of marine dinosaurs are found in the sand-like soil of Morden, about 100 kilometres southwest of Winnipeg.

The treasure trove of skeletons discovered just outside the town prompted enthusiasts in 1979 to pool their collection of ancient bones and establish what is now the country's largest collection of marine reptile fossils.

Paleontologists have continued to dig up an escarpment around Morden and announced the discovery of a mosasaur and massive Xiphactinus fish last summer. That same site has produced the most recent windfall of buried fossilized treasure, including another fierce mosasaur.

"They were definitely on top of the food chain," Janzic said. "They even preyed upon other mosasaurs."

Mosasaurs were huge oxygen-breathing lizards, up to 15 metres long, that propelled themselves though the water by moving their tail from side to side. They boasted two sets of teeth and a jaw that could dislocate at will, allowing them to feast on just about anything they wished.

The sea creatures vanished, along with the terrestrial dinosaurs, around 65 million years ago.

Evidence from the Morden dig site seems to suggest their environment was changing. Joseph Hatcher, an assistant curator who is sifting through the geological clues, said something happened to disrupt the ecosystem.

Sediment had been building up very slowly in the ocean, he said.

"Then something changed at the Earth's surface, be it a storm surge or something going on with the climate, where all of a sudden there was a massive influx of sediment into the water -- very quickly -- that's churned everything up."

The sudden shift may have been linked to the formation of the Rocky Mountains or significant volcanic activity at the time.

After that, a new type of shale appeared, which contained minute fossils, invisible to the naked eye. Where before there were massive mosasaurs, Hatcher said now there are only "tiny, tiny little fish fossils."

"We see a large changeover in the animal life," Hatcher said. "It's a pretty big deal."

With only a handful of people working on the dig, Janzic said it will probably be several years before all the fossils are carefully retrieved and polished. The group will eventually write up its findings for academic journals and will probably present preliminary results at a symposium this fall, she added.

"We'll clean it up," said Janzic as she took a break from washing the teeth of the recently discovered mosasaur. "At that point, we can analyze the bones or fossils and look for bite marks, look for pathologies and then we will publish on it."

Chinta Puxley, The Canadian Press