Mosasaurus

Mosasaurus ("lizard of the Meuse River") was a genus of mosasaur, a carnivorous, aquatic lizard, somewhat resembling a flippered crocodile, with elongated heavy jaws. The genus lived in the Maastrichtian age of the Cretaceous period (Mesozoic era), around 70-65 millions years ago in the area of modern Western Europe. The genus Capelliniosuchus, once thought to be a metriorhynchid crocodylian, is a junior synonym of Mosasaurus.

History
Mosasaurus was the first genus of mosasaur to be named. The first remains known to the science was a fragmantary skull from a chalk mine near Maastricht, the Netherlands found in 1766. It was initially believed to belong to a crocodile by G. Cuvier, but subsequently identified as a huge lizard. In 1822 W.D. Conybeare named it Mosasaurus after the Latin name (Mosa) of the Maas (Meuse) River passing through Maastricht. The species name (epithet) "hoffmannii" was added by G.A. Mantell in 1829, honouring the military surgeon C.K. Hoffmann, who originally recovered the type specimen.

Evolution
As with most mosasaurs, their legs and feet are modified into hydrofoil-like flippers, with the forelimbs larger than the hindlimbs. The first mosasaur ever discovered, Mosasaurus hoffmannii, was excavated in a mine near Maastricht, the Netherlands in the 1770s. Like its American relatives Tylosaurus and Hainosaurus, Mosasaurus reached lengths of about 15 meters. However, Mosasaurus was much more robust than tylosaurine mosasaurs, at some double the weight of a mosasaur of the same length. In life, a 10 m long Mosasaurus was as heavy as a 15 m long Tylosaurus.

Anatomy
Mosasaurus was among the last mosasaur genera, and among the largest. The skull was more robustly built than other mosasaurs, as the mandibles articulated very tightly with the skull. It had a deep, barrel-shaped body, and with its fairly large eyes, poor binocular vision, and poorly developed olfactory bulbs, experts believe that Mosasaurus lived near the ocean surface, where it preyed on fish, turtles, ammonites, and possibly smaller mosasaurs. The animal remained near the surface and although it was able to dive, it did not venture into deeper waters.

The skull of Mosasaurus tapered off into a short, conical process, and the jaws were armed with massive, sharp, conical teeth. Their paddle-like limbs had five digits in front and four in back. The trunk terminated in a strong tail which, together with serpentine undulation of the whole body, contributed far more to the animal's locomotion that did the limbs.

Because of its robust skull and tightly articulating jaws, Mosasaurus was unable to swallow prey-items whole in the manner of earlier mosasaurs, such as Tylosaurus. Instead, with the aid of its curved, knife-like teeth, Mosasaurus was able to tear its prey into more manageable pieces that could be more easily swallowed.

As mentioned before, Mosasaurus was discovered near the town of Maastricht, located at the southernmost tip of the Netherlands. The city is largely built with blocks of limestone from the town's quarry. In 1770, the local Dutch army physician, Dr Hoffmann, who had developed an interest in the strange bones that kept showing up in these blocks of limestone, paid the quarrymen extra to look out for especially large specimens. The best of these was found in 1774, and it was named Mosasaurus hoffmannii. It was a very controversial find, as the skull belonged clearly to a species that no longer existed on earth, and it raised the first speculations on the possibility of animal species going extinct. The idea of extinction paved the way for the theory of "several creations", one of the predecessors of the evolution theory. A few years after the find, the French armies occupied Maastricht and the fossil skull was taken to Paris, where it is was studied by G. Cuvier. The skull still on display in the Muséum National d'Histoire Naturelle.

In 1998, another, even bigger and more intact fossil Mosasaurus skull was found in the Maastricht limestone quarries. It was nicknamed "Ber" and it is currently on display in the Maastricht Natural History Museum.

Relatives
The family Mosasauridae is split into several subfamilies, with Mosasaurus being placed within Mosasaurinae. This subfamily, in turn, is further split into smaller tribes, with Mosasaurus being grouped with Clidastes, Moanasaurus, Amphekepubis, and Liodon in the tribe Mosasaurini.