Mosasaurus was a genus of mosasaur, giant carnivorous, aquatic lizards, somewhat resembling flippered crocodiles, with big elongated jaws.
This genus existed during the Maastrichtian age of the Cretaceous period (Mesozoic era), around 70–66 million years ago in the area of modern Western Europe and North America in a western interior sea and was one of the last mosasaurs. Its name means "Meuse river lizard", as its fragmentary skull was found near the Meuse River in 1764 by lieutenant Jean Baptiste Drouin. It was similar to the North American Tylosaurus, but at 18.5 meters (61 feet) in length, it was even smaller and bigger.
It was initially thought to be a species of whale or crocodile considering its large teeth but De Saint-Fond still assumed the specimen represented a crocodile. In 1798 the son of Petrus Camper, Adriaan Gilles Camper, studied the fossil indirectly by reconsidering the description by his father. He was the first to reach the conclusion that the remains were those of a giant monitor lizard, which result in 1799 he corresponded to Georges Cuvier who formally identified it as a completely new but extinct creature (at the time extinct animals were assumed to be like extant animals but giant).
Mosasaurus had unusual skull anatomy which is actually double-hinged like a snake (albeit aquatic and with fins). How it did this is when it was biting down on something large, its jaws would dislocate and unhinge so it would be able to take bigger bites. Its fins were probably used for steering and balance when swimming, not like plesiosaurs who used their fins as their primary means of locomotion. It was very elongated and thin in the body so it was more streamlined so it could move faster for longer periods of time than plesiosaurs who could only accelerate for short periods. Mosasaurus probably had a strong bite force due to eating prey like giant turtles in its time. There are some other species of mosasaur that specialised in eating this kind of prey so they had stronger bites than Mosasaurus who was a generalist predator so it would take anything that fit into its mouth, not unlike tiger sharks today. It is assumed that mosasaurs swam alone since their bite marks have been found on other mosasaurs indicating aggression and territoriality among the species. Mosasaurus more than likely used the same tactics sharks use today to hunt large prey such as plesiosaurs and ichthyosaurs by going down far beneath the prey and getting one devastating surprise attack to avoid injury. To achieve this tactic, It was probably counter shaded so its top was dark to camouflage against the dark ocean below the target and light underneath to camouflage against the sun's bright light. It was also possible that mosasaurus actively chased down its food by using explosive speed and stamina to hunt prey like ichthyosaurs.
It has been recently discovered that the mosasaur genus Platecarpus has a tail fluke on its tail which would aid with swimming. It is not unlikely that other mosasaurs if not all mosasaurs had this tail fluke to achieve even better swimming capability.
- A Mosasaurus was featured prominently in Jurassic World, the fourth film in the Jurassic Park series. According to the park staff, the Mosasaurus is a female. It is shown breaching on water to consume a great white shark hanging above the surface. It lives in a 3,000,000 gallon pool in Jurassic World Lagoon during the feeding show. The visitors are also taken to an underwater viewing station to have a closer look at the Mosasaurus.
- Mosasaurus has a few scene appearances in this installment. It is later seen eating one of the Pteranodon's that escaped the aviary when the Isla Nubar incident occurs. It is last seen pulling the Indominus rex (a fictional hybrid dinosaur) under the water during the final battle with Rexy the Tyrannosaurus rex and Blue the Velociraptor and saving the park.
- Mosasaurus was confirmed for Jurassic World: Fallen Kingdom by Chris Pratt and Bryce Dallas Howard. The individual Mosasaurus seen in Jurassic World has survived the years it has spent on Isla Nublar, although it, alongside many other creatures, will now face an impending danger in the form of an erupting volcano. The Mosasaurus has been confirmed on the Jurassic World website to have escaped into the ocean. She was last seen in the open ocean attacking surfers.
- In Jurassic Park Builder, Mosasaurus can be created in the aquatic section of the park as a limited edition "dinosaur".
- In Jurassic World: The Game, Mosasaurus is a legendary surface sea reptile. At first, it could only be seen swimming in the Jurassic World Lagoon without the player being able interact with it, create it, or use it in the battle arena. This was until September 30, 2015 when the Mosasaurus appeared. Since then, the shadow in the lagoon has disappeared until you get the mosasaur. It was only available in either winning it in the Mosasaurus tournament or win it by spinning the tournament wheel and landing on it, but it now can be obtained by either purchasing an Aquatic Card Pack, or winning an Aquatic Card Pack that contains it from the arena.
- Mosasaurus will be in the upcoming game, Saurian, although the genus isn't found in Hell Creek, which is a terrestrial deposit. Rather, it'll be an animal that is found far out to sea on the world map since South Dakota (which is where the game is set) was near the Western Interior Seaway during the Cretaceous.
- It also appears in the tie-in game LEGO Jurassic World where it can be unlocked as a playable prehistoric animal.
- A Mosasaurus nicknamed 'Mr. Snappy' is a playable character in the game Hungry Shark Evolution.
- Mosasaurus appeared on Dinosaur Train.
- A Mosasaurus appeared in one of the episodes in the first series of Primeval.