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Real monsters of the deep — new marine reptile fossil discovery
Oct 03, 2008

The Morden and District Marine Museum is about to add another giant to its fossil collection. It already possesses a 43-foot-long reproduction of Manitoba’s most famous reptile of the deep nicknamed “Bruce,” whose fossil remains were uncovered in 1974 north of Thornhill, Manitoba.

Morden has long been famous among the small community of palaeontologists as possessing one of the best troves of mosasaur and plesiosaur fossils. But, the most recent find of a plesiosaur by a man walking through a cow pasture is bringing it plenty of media attention and alerting the Manitoba public to a treasure in their own backyard.

Joe Brown, a self-described amateur palaeontologist, searches for fossils in connection with the Morden museum. His discovery was made last year but uncovering the fossil of a near complete skeleton was only started this year.

Brown made the fossil find while on his way to a nearby field where he was digging up the remains of a mosasaur. This site lacked the dramatic impact of his later find since it contained fewer and less significant remains.

After literally stepping on the plesiosaur fossil, he started initial excavations using a paint brush which revealed the extent of skeletal remains. The first bone uncovered was a clavicle, the largest bone of the sea creature. Other bones followed in quick succession, and Brown knew he had stumbled upon the find of his lifetime.

This discovery adds to a rich tradition of fossil collecting in the Pembina Hills area. The uncovering of these true-life sea monsters, led to the Morden museum signing an agreement to sell replicas of the museum’s short-necked plesiosaur, a creature which swam in the sea covering Manitoba 80 million years ago.

Prehistoric Animal Structures of East Coulee, Alberta received the rights to make replicas which are sold to museums across the globe for about $15,000. The replicas will be made from a mould taken from the museum’s three-metre long plesiosaur. Each copy of the original fossil will bear the name of the Morden museum.

Bruce is an example of mosasaur scientifically called Hainosaurus pembinensis, and is the largest mosasaur found in North America. The museum  also possesses a replica of a short-necked plesiosaur skeleton of a species called Trinacromerum by the Alberta firm which was excavated in 1972. The fossil skeleton of the aquatic reptile was nearly 100 per cent complete.

During the Cretaceous (135 to 65 million years ago), the North American continent was divided into two large land masses separated by the Mid-Continental Seaway which was 1,600 kilometres wide and stretched from Canada’s north to the Gulf of Mexico. It was a time of lush tropical and 

subtropical forests when dinosaurs roamed the earth and when Manitoba was home to some of the strangest marine creatures that evolution could fashion — plesiosaurs and mosasaurs cavorting in the salt seas of North America.

There is no need to invoke the 

image of Nessie, the famous mythical creature of Loch Ness, for Manitoba was home to real monsters of the deep.

Mosasaurs

Mosasaurs, named after the Meuse River in Belgium where the first fossils were found in 1870 — Mosa is the Latin form of Meuse, while saur is a shortened form of the Greek saurus for lizard — are considered by palaeontologists as the most fearsome and successful of the air-breathing 

marine reptiles. It descended from a land-based monitor lizard-like reptile.

Mosasaurs ranged from about three to five metres in length on average, but there is one fossil specimen on display in the Morden museum of this family of reptiles that could reach almost 20 metres in length.

The jaws of a mosasaur were designed with a joint in the middle of each mandible to expand its gape outward and capture large prey. Judging by its razor-sharp, recurved teeth structure and inner teeth in the upper palate to hold its prey, the most common prey of the mosasaur was probably slippery fish, but it also could have added the odd giant squid like today’s deep-diving sperm whale.

The fact that mosasaurs were divers is attested to by a bony plate 

inside their eyes, called a sclerotic ring, which protected them against the extreme pressures of the deep.

Mosasaurs possessed a long muscular tail, and moving this tail side-

to-side, a mosasaur could move swiftly through water. Its legs had evolved into paddles —the back limbs were probably swept back while swimming to cut down on drag and the fore limbs probably served as stabilizers and aided in quick directional changes.

It is believed that the large body size and their lack of true legs prevented mosasaurs from pulling themselves up onto beaches and laying eggs in the sand like alligators, crocodiles and sea turtles do today. Instead, they probably bore live young at sea.

Plesiosaurs

Plesiosaurs also evolved from a land-based reptile and have been 

described as “a snake, threaded through the body of a turtle,” though lacking a turtle’s shell. They had heavily-constructed bodies, short tails and four powerful paddles used to swim — actually fly through the water like penguins — and steer.

Among the plesiosaurs, Elasmosaurus was a behemoth, possessing a long snake-like neck made up of more than 70 vertebrae. Its head was small in proportion to its body. The Iong neck has convinced palaeontologists that plesiosaurs were surface feeders, even suggesting that their long neck allowed them to snatch birds from out of the sky. But it is more likely that their most common prey was fish caught with needle-sharp teeth.

The recent Morden find has thus far  revealed 15 teeth, which are 

described by museum officials as 

still sharp after millennium of being buried.

Plesiosaurs had teeth designed 

for tearing, not chewing, so they 

swallowed rocks to grind their food, such as an ostrich does today. These stomach stones, or gastroliths, are quite frequently where the stomach would have been when a fossil 

skeleton is unearthed, particularly 

in the case of large land-based dinosaur herbivores such as diplodocus which used huge stones to grind up vegetable matter in their massive 

stomachs.

There was also a short-necked 20 vertebrae variety of streamlined, swift plesiosaur with a large head called Pliosaur (the specimen found in the Morden museum which provided the mould for the sale of replicas). In some of its forms, the head could account for up to a quarter of its body length. Bruce’s skull is a formidable five-feet long. 

Its teeth were large and apparently better suited for eating cephalopods — squid, cuttlefish and octopi — found in deeper waters. Thus, they may have competed with the mosasaurs. In fact, the appearance of fierce mosasaurs on the scene caused a diminishing in the number of 

plesiosaurs in the world’s oceans.

Like dinosaurs, plesiosaurs and mosasaurs died out 65 million years ago. Many believe the mass extinction was the result of a massive meteorite striking the earth and throwing a dense cloud of debris into the upper atmosphere which created a nuclear winter-like scenario that dinosaurs and the marine reptiles could not survive. One such strike has been found just off the Yucatan Peninsula in Mexico and dates back to the time of the extinction. Its crater size is sufficient in diameter and depth to have thrown up enough of a debris cloud to block out much of the sun’s life-giving rays for years.

Still others believe the dinosaurs were already diminishing in number of species and thus were on their way out when the meteorite struck.

Whatever the explanation, without dinosaurs around, the small warm-blooded, shrew-sized mammals were given the opportunity to become the dominate species on the earth.