Mosasaurus

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***Mosasaurus*** was a genus of mosasaur from the Late Cretaceous period. Mosasaurus were 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 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.

Tail muscles gave *Mosasaurus* the power needed for ambush attacks.

## Research history

### First discoveries

*Mosasaurus* was the first genus of mosasaur to be named. The first remains known to science were a fragmentary skull from a chalk quarry in the St Pietersberg, a hill near Maastricht, The Netherlands, found in 1764 and collected by lieutenant Jean Baptiste Drouin in 1766. It was in 1790 described as a fish but not named, by Martinus van Marum, the first director of the Teylers Museum at Haarlem. The same year Van Marum procured the fossil for the museum; it is still part of the collection as TM 7424.

At some time between 1770 and 1774 (the often mentioned date of 1780 is incorrect) a second partial skull was discovered and procured by canon Theodorus Joannes Godding, who displayed it in his country house on the slope of the hill. A local retired German/Dutch army physician, Johann Leonard Hoffmann, also collected some fragments and published about the skull; his correspondence with international scientists made the find world famous. Hoffmann presumed the animal was a crocodile. In 1786 however, the Dutch Profesor Petrus Camper disagreed and concluded the remains were those of an unknown sperm whale, of a *Physeteris incogniti ex Monte S. Petri*.

In 1794 Maastricht, an important fortress city, was captured by the French revolutionary armies. Accompanying the French troops was geologist Barthélemy Faujas de Saint-Fond on a mission to secure the piece, together with *représentant du peuple* (political commissar) Freicine who during the campaign tried to transport anything of artistic or scientific value he could lay his hands on to France. Finding that it had been removed from the cottage and hidden within the fortress, Freicine offered "six hundred bottles of good wine" to those troops being the first to locate the skull; soon a dozen grenadiers claimed their reward, carrying the piece with them. Early 1795 it was moved to Paris as war booty, by decree declared a national heritage and added to the collection of the new Muséum national d'Histoire naturelle.

In 1799 Faujas de Saint-Fond published his *Histoire naturelle de la montagne de Saint-Pierre de Maestricht [Tome 2]* which also contained an account of the circumstances of the find. According to him Dr Hoffmann paid the quarrymen extra to look out for especially large specimens. When the skull was found on 1770 Hoffmann would have been present during the excavation. Afterwards Godding would have claimed his rights as landowner and forced Hoffmann to relinquish his ownership through a lawsuit, won by influencing the court. De Saint-Fond would nevertheless in 1795, saving the specimen for science, have paid a considerable indemnity to Godding to compensate for his loss. However, as Dutch historian Peggy Rompen showed, of this famous story very little can be substantiated by other sources. Godding was the original owner, Hoffmann clearly never possessed the fossil, there was no lawsuit, de Saint-Fond probably never paid anything and the entire account seems to have been fabricated by him to justify the dispossession by military force.

De Saint-Fond still assumed the specimen represented a crocodile. In 1798 the son of Petrus Camper, Adriaan Gilles Camper, again 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, which result in 1799 he corresponded to Georges Cuvier.

In 1808 Cuvier confirmed Camper's result. The fossil had already become part of Cuvier's first speculations on the possibility of animal species going extinct. The idea of extinction paved the way for his theory of catastrophism or "consecutive creations", one of the predecessors of the evolution theory.

A scientific name had not yet been given to the new species, the specimen usually being referred to as the *Grand Animal fossile des Carrières de Maëstricht* or "Great Fossil Animal of the Maastricht quarries". In 1822 William Daniel Conybeare named it *Mosasaurus* after the Latin name (*Mosa*) of the Maas (Meuse) River passing through Maastricht, the second skull being the holotype, **MNHNP AC9648**. The specific name (epithet) *hoffmannii* was added by G.A. Mantell in 1829, honouring surgeon C.K. Hoffmann, on the presumption he was the discoverer of the type specimen. Today the emendated form *hoffmanni* is most often used.

In 1854 German biologist Hermann Schlegel was the first to conjecture *Mosasaurus* had flippers instead of normal feet.

In 1998, another, even bigger and more intact fossil skull was found in the Maastricht limestone quarries, nicknamed "Bèr", and displayed in the Maastricht Natural History Museum. However, it was determined this find represented a new species of the genus *Prognathodon*.

## Description

*Mosasaurus* was a type of derived mosasaur, a latecoming member that has evolved advanced traits such as a fully aquatic lifestyle. As such, *Mosasaurus* had a streamlined body, elongated tail that ended with a hypocercal downturn that supported a two-lobed fin, and two pairs of flippers. While in the past derived mosasaurs were depicted as akin to giant flippered sea snakes, it is now understood that they were more similar in build to other large marine vertebrates such as ichthyosaurs, marine crocodylomorphs, and archaeocete whales through convergent evolution.

### Size

The type species of *Mosasaurus* is one of the largest mosasaurs known.

## Classification

### History of taxonomy

Because the rules of nomenclature were not well defined at the time, 19th century scientists did not give Mosasaurus a proper diagnosis during its first descriptions. This led to ambiguity regarding the definition of the genus, which led it to become a wastebasket taxon that contained as many as fifty different species. The taxonomic issue was so severe that there were cases of species that were found to be junior synonyms of species that were found to be junior synonyms themselves. For example, four taxa became junior synonyms of M. maximus, which itself became a junior synonym of M. hoffmannii. This issue was recognized by many scientists at the time, but efforts to clean up the taxonomy of Mosasaurus were hindered due to a lack of a clear diagnosis.

## 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 most likely 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.

## 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.

## Paleobiology

### Head musculature and mechanics

Much of the knowledge on the musculature and mechanics of the head of Mosasaurus are largely based on Lingham-Soliar's 1995 study on M. hoffmannii skulls. Because soft tissue like muscles do not easily fossilize, reconstruction of the head musculature is largely based on the structure of the skull, the nature of muscle scarring on the skull, and the musculature in extant monitor lizards.

## Paleoecology

### Distribution, ecosystem, and ecological impact

Excluding the Pacific species unassessed by Street and Caldwell (2017) and identified as separate genera in Street (2016), Mosasaurus was a transatlantic mosasaur with its fossils having been found in marine deposits on both sides of the Atlantic Ocean. These localities include the Midwestern and East Coast of the United States, Canada, Europe, Turkey, Russia, the Levant, the African coastline from Morocco to South Africa, Brazil, Argentina, and Antarctica.

## Extinction

By the end of the Cretaceous, mosasaurs like Mosasaurus were at a height of evolutionary radiation, and their extinction was a sudden event.

## Appearance in other media

### *Jurassic Park*

* 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 *Pteranodons* that escaped the aviary when the Isla Nublar 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.

## References

* Bardet, N. and Jagt, J.W.M. 1996. *Mosasaurus hoffmanni*, le “Grand Animal fossile des Carrières de Maestricht”: deux siècles d’histoire. Bulletin du Muséum national d’Histoire naturelle Paris (4) 18 (C4): 569–593.
* Benes, Josef. Prehistoric Animals and Plants. Pg. 144. Artia, 1979
* Mulder, E.W.A. 1999. Transatlantic latest Cretaceous mosasaurs (Reptilia, Lacertilia) from the Maastrichtian type area and New Jersey. Geologie en Mijnbouw 78: 281–300.

1. ↑ M. van Marum, ‘Beschrijving der beenderen van den kop van eenen visch,…’, *Verhandelingen Teylers Tweede Genootschap* **9** (1790), p. 383-389
2. ↑ Mulder, Eric Wolfgang Amadeus. 2004. "Maastricht Cretaceous finds and Dutch pioneers in vertebrate palaeontology". In: Touret, J.L.R. & Visser, R.P.W. (eds). *Dutch pioneers of the earth sciences*, pp. 165-176. Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam
3. ↑ P. Camper, "Conjectures relative to the petrifactions found in St. Peter’s Mountain near Maestricht", *Philosophical Transactions*, **76**: 443-456
4. ↑ P. Rompen, 1995, *Mosasaurus hoffmanni: De lotgevallen van een type-exemplaar*
5. ↑ A.G. Camper, 1800, "Lettre de A.G. Camper à G. Cuvier sur les ossemens fossiles de la montagne de St. Pierre, à Maëstricht", *Journal de Physique* **51** (1800) p. 278-291
6. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `Penza`