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Mosasaurs were large marine reptiles which had flippers instead of terrestrial limbs. Sometimes referred to as the “T. rex of the Sea” the Mosasaurs ruled the Western Interior Seaway between 80 and 90 million years ago. Early into their evolution, mosasaurs enjoyed a rapid speciation, becoming the top predators of the Cretaceous oceans, reaching sizes of over 15 m (50 feet). However, their rule over the oceans would be short lived in the geological record, as they became extinct along with many of their reptilian counterparts during the great Cretaceous – Paleogene Extinction. It was this famous extinction event which also eliminated the dinosaurs from the world’s terrestrial habitats.
The fossilized remains of the mosasaurs would remain hidden deep in the rocks until they were first discovered in the 1770’s in an underground mine near Maastricht, on the Meuse River, in Holland. This predates the first dinosaur discovery by almost 50 years!
Since that time, mosasaur remains spanning a large variety of genera have been recovered from sedimentary rocks all over the world. They are one of the most often studied marine reptile groups, yet their exact habits and diets can only be hypothesized based on a wealth of paleontological knowledge. Some paleontologists believe that mosasaurs were primarily surface swimmers, bottom dwellers, and/or deep divers. Being reptiles, we know that mosasaurs had to surface to breathe air. However, their biotic zone of preference within the world’s oceans remains unknown. Nevertheless, all mosasaurs swam in a similar fashion which would later become typical of all Squamates due to the convex and concave surfaces of the vertebrae. Using their long rudder-like tails, the mosasaurs would perform snake-like undulations propelling themselves forward while their flippers were used for steering.
Mosasaurs were the dominant predator preying on everything in sight that could be killed and swallowed by their awesome jaws. Possessing two sets of teeth with a moveable lower jaw made mosasaurs the most feared animals of the ancient seas.
There were many different types of mosasaurs around the world during the Cretaceous, but here in Manitoba there were three main genera (or groups). These include Clidastes as the smallest mosasaur found locally at a size range between 3 and 6 m (10-20 feet) in length. Clidastes had a small and narrow skull well suited to preying upon fish and sharks; Platecarpus and Plioplatecarpus were more medium in size, approximately 6 to 9 m (20 – 30 feet) in length and had more robust jaws and teeth, well suited to preying upon other marine reptiles; Hainosaurus and Tylosaurus were the largest of the mosasaurs between 10-15 m (40-50 feet) in length with large and robust skulls capable of devouring anything it wanted!
Our famous “Bruce” is the world's largest publicly displayed mosasaur. Bruce is approximately 13 m (43 feet) long and was given the scientific name of Hainosaurus pembinensis by Dr. Elizabeth Nicholls in 1988. Bruce was discovered north of Thornhill, Manitoba in 1974 and the huge skeleton took almost two full field seasons to excavate. The skeleton is reasonably complete, with about 65 – 70% of the fossilized bones recovered.