Mosasaurus maximus (S/F)

mosasaurus-detail-headernublarindicatorMosasaurus maximus was an extremely large species of marine mosasaur. The “Meuse River lizard” was discovered by Johan Leonard Hoffman and formally given a full scientific name by William Mantell in 1829. Mosasaurus lived during the late Cretaceous period from 70 to 66 million years ago. Mosasaurus belonged to the family Mosasauridae, and its bones have been recovered from Western Europe and North America. This particular species, M. maximus, was found in the Fox Hills Formation, which stretches from Alberta to Colorado. Its specific epithet “maximus” refers to its size, as it is the largest species of Mosasaurus.

There are several species of Mosasaurus known. The type species (and largest known in real life) is M. hoffmanni, a fifty-six-foot reptile with which M. maximus is typically considered synonymous. In the Jurassic film franchise, scientists determine that Mosasaurus maximus is its own distinct species, instead of being the same thing as M. hoffmanni, thus making M. maximus the largest known species instead. Other species include M. conodon, M. lemonnieri, M. beaugei, and M. missouriensis.

On August 25, 2000, InGen’s Dr. Henry Wu reported that researchers Bridges and Curtis, et al. at their San Diego location had utilized a prototype of a new iron analyzer to discover traceable DNA fragments in a recently-discovered fossil mosasaur skeleton. With this new technique, InGen was able to reliably clone marine animals; until the invention of the iron analyzer, a lack of amber samples containing parasites which had fed on marine life would make the DNA of these animals an extreme rarity. After this animal was cloned in 2006 or 2007, the immense size that it grew to led InGen researchers to conclude that it was Mosasaurus maximus, according to a statement made on March 20, 2015 by Dr. Brian Switek.

DPG report on the mosasaur (6/8/2018)

Only one member of this species is known, so the physical appearance may be more variable than has been thus far observed.

The most striking feature of M. maximus is, of course, its size. Most infographics in Jurassic World’s attractions state that it reaches lengths of fifty-five feet, which is consistent with paleontological knowledge. However, even a passing glance at the specimen from the park reveals that it is noticeably larger. The Jurassic World website and a May 2015 article by Dr. Brian Switek state that the animal is sixty feet long, which would make it slightly larger than known specimens. The Jurassic World Facts mobile application gives it a length of 71.8 feet long. The books The Park is Open and Jurassic World: Where Dinosaurs Come to Life, which released in May 2015, list the mosasaur’s length as 72 feet (The Park is Open is more precise, at 72.2 feet). The mosasaur appears to continue growing throughout its life, as a June 8, 2018 social media post by the Dinosaur Protection Group lists its length at 84.9 feet and a weight of 30 tons. However, its size in 2018 appears to have increased immensely, reaching around 120 feet; this would make it the largest known vertebrate of all time. Weight estimates have also varied; Jurassic World social media has listed it at 28 tons, while the official website listed it at both 15 tons and 5 tons at different places on the site. As five tons is an extreme low outlier in the weight estimates, it is most likely an error on the part of the website.

A post from Jurassic World social media giving one of several weight and length estimates for the Mosasaurus.

Notably, the vast size this animal reached when in captivity makes it the largest carnivorous vertebrate ever known, though some planktivorous whales such as the blue whale are still larger. It is also exceeded in length by some of the largest sauropods, though these are terrestrial herbivores. When in the wild, the maximum known size is closer to 120 feet, meaning it is longer than all known animals except for the longest-recorded lion’s mane jelly (Cyanea capillata), which also reached 120 feet long including the tentacles, and possibly the bootlace worm (Lineus longissimus), which has been reported at 180 feet long when stretched out.

The second most noticeable feature of the mosasaur is its enormous mouth, lined with 88 sharp, cone-shaped teeth. Its upper palate has a secondary row of teeth which assist it in handling live prey. The mouth is capable of opening very wide, and when biting down, exerts 13,000 pounds of force. This exceeds the bite force of Tyrannosaurus rex. Its muscular tongue is comparatively short; it is thick and pointed rather than forked, and is pink in color. Within the mouth, the mosasaur can be seen to have choanae, or nasal openings. This would allow it to smell through its mouth, though it lacks external nostrils and would still have to open its mouth above the surface to breathe. The skull itself is very long, consisting mostly of the jaws, and tapers to a point. Its eyes have yellow sclerae and round, black pupils.

Detail on the left eye of an adult female M. maximus

Instead of feet, all mosasaurs have four paddle-like flippers which are too small to use for propulsion. They are utilized for steering, and the front flippers have some limited use when the animal rests on a solid surface. It is unable to walk or crawl on land due to its enormous bulk and lack of muscular limbs, but its front flippers can help it maintain stability and shift the front half of its body left and right.

Because it inhabits salt water, the mosasaur must have salt glands for osmoregulation. In birds and reptiles, salt glands are located in or on the head, generally near the eyes, nostrils, or mouth. In the only modern marine lizard, the marine iguana Amblyrhynchus cristatus, excess salt is expelled through the nostrils. The exact location of the mosasaur’s salt glands is unknown.

Its long, tapering body is protected by scaly skin, including several rows of particularly large and thick scales on its dorsal side. These give the appearance of osteoderms similar to those of crocodilians, a feature not known in mosasaurs or their relatives. In addition, a row of tall triangular scales runs down the dorsal side all the way to the tail. Like most marine animals, it exhibits countershading, with a darker blue-gray color on the dorsal side and lighter on the underside.

The lengthy, powerful tail of the Mosasaurus is used for propulsion through the water, while the flippers assist in steering.

The body of this mosasaur terminates in a lengthy tail with a large hypocercal caudal fin. This means that the vertebrae extend into the lower lobe of the fin, making the lower lobe larger. In the case of the only known cloned Mosasaurus, the upper lobe is so much smaller than the lower lobe that it can be missed at a cursory glance. The mosasaur’s caudal fin is often called a “fluke,” like the tail of a whale; however, the mosasaur’s tail fin is anatomically very different from a whale’s, and has more in common with the tails of certain fish. Powerful strokes of the tail are used to propel the mosasaur through the water.


Only the adult stage of the Mosasaurus maximus has been observed. The mobile game Jurassic Park Builder features a Mosasaurus hoffmanni with no relation to the mosasaur housed in Jurassic World, portraying the juvenile stage as a smaller version of the adult.

While this animal’s natural growth rate is unconfirmed, the female bred in 2006/2007 reached its original projected length by 2014. It is not known if it was given any kind of growth-boosting supplements. Between December 18, 2015 and June 2016, its listed length increased by 12.7 feet; if these measurements are accurate, its daily growth rate for that period of time was 2.12 feet per month. After it was reported missing, its size increased to 120 feet. If it attained this size between June 2016 and June 24, 2018, this would mean it grew 35.1 feet in the intervening two years. This would put its growth rate for that time at 17.55 feet per year, or 1.46 feet per month.

Sexual Dimorphism

Only the female Mosasaurus has been cloned. Thus, any sexual dimorphism remains unknown.

Preferred Habitat
Detail on the mosasaur’s mouth as it prepares to consume prey. Note the tongue, secondary row of teeth on the upper palate, and choanae.

This reptile inhabits nearshore marine environments, though its bulk requires it to maintain some distance from intertidal zones. If it is to approach land, it must have an immediate steep drop-off so that it does not become stranded. As most of its prey inhabits surface waters, this animal does not dive terribly deep. While it was bred in tropical waters, its size would make it gigantothermic, so its sheer bulk would protect it from colder temperatures. The extent of the mosasaur’s tolerance for temperature is thus far unknown. At adult size, it requires a habitat containing at least three million gallons of salt water.

Isla Nublar

A single female Mosasaurus maximus was bred on Isla Nublar. It was stated to be 11 years old as of May 15, 2018, meaning it was bred sometime between May 16, 2006 and May 15, 2007. It was placed in the Jurassic World Lagoon, where it was kept on exhibit until the park closed on December 18, 2015. At an unknown date in June 2016, human interference allowed the mosasaur into the canal system that fed the lagoon, from which point the mosasaur escaped via the island’s waterways into the surrounding ocean. It is not known how long it remained near Isla Nublar following this incident, though the Jurassic World: Fallen Kingdom Survival Guide suggests that it remained in that area for some time.

Isla Sorna

While the Muertes Archipelago is certainly within the mosasaur’s ideal range, there is no evidence that the only known individual ever ventured there.

Concept art for a mosasaur breeding tank was drawn up for Jurassic Park ///, but ultimately was cut from the film; there is no evidence that mosasaurs were bred on Isla Sorna.


Following its escape from Isla Nublar in June 2016, the Mosasaurus spent two years roaming the East Pacific Ocean before being sighted near the West Coast of the Americas on or after June 24, 2018. Its exact location is not known.

Behavior and Ecology
Daily Activity

The mosasaur is primarily diurnal, but is known to be active during both the day and night. The behavior of the individual in Jurassic World was heavily influenced by the park’s schedule, as it was given food every two hours during the park’s operation; as the park was open from 8:00 AM to 10:00 PM, and the first scheduled mosasaur feeding at 9:00 AM, the mosasaur would be fed six times during the day. Once in the wild, it appears to hunt primarily during the day. When at rest, it floats in the water column rather than directly on the surface.

The mobile game Jurassic World: The Game portrays Mosasaurus maximus as being active for twelve-hour periods at a time, which matches up with the time elapsed between the first and last feeding shows of a standard day at Jurassic World (the first being at 9:00 AM, then every two hours until the park closes; this would mean the last feeding show would be at 9:00 PM).

Diet and Feeding Behavior

According to Jurassic World personnel, the normal diet of Mosasaurus maximus consists of fish, ammonites, birds, and marine reptiles such as turtles and smaller mosasaurs. InGen cloned great white sharks (Carcharodon carcharias) at an offsite location to be part of the mosasaur’s diet; it was fed a subadult female shark on 12/18/2015 as one of its last prepared meals, and the Jurassic World website indicates that sharks were its typical food items.

This animal is not a picky eater, consuming virtually any available prey. Its diet includes terrestrial animals that venture too close to the water’s edge, as well as flying animals such as Pteranodon. According to the LEGO Jurassic World game, the Mosasaurus can open its lower jaw wide enough to swallow food larger than its own head, but it is not seen to do this in the films.

Jurassic World’s Mosasaurus consumes an escaped Pteranodon and Jurassic World employee Zara Young in typical predatory breaching attack (12/18/2015)

Mosasaurus tends to be a messy eater when preying on larger animals. Its first intent is to kill the victim, so it often breaks the prey apart while attacking. If it can swallow prey whole, it will attempt to; the secondary set of teeth in its upper palate prevents slippery prey, such as fish, from escaping and forces them toward its throat. If the mosasaur loses any chunks of prey while making the initial bite, it will usually return to consume these after swallowing the first chunk. It kills by clamping its jaws shut around the prey item, typically around the midsection or neck, slamming the prey item into the water’s surface, and thrashing it around underwater. It attacks prey from below, often breaching in the process of capturing its prey.

The mosasaur’s food is torn into chunks large enough to swallow, but it is often a wasteful eater if its prey is particularly large; for example, about half of the Indominus rex remained uneaten after it was killed by the Mosasaurus. The rear half of the animal had been consumed, leaving the skull, most of the ribcage, and one arm intact.

The Mosasaurus exhibits the first known case of ambush-feeding on a terrestrial prey item (12/18/2015)

Ambushing terrestrial prey is a riskier maneuver for the mosasaur, but on Isla Nublar this behavior was rewarded with much larger prey items. Few large animal remains were seen on the floor of the Lagoon, however; it is likely that this method of hunting was only used on rare occasions.

Mercenaries hired by Eli Mills and Henry Wu speculated that the Mosasaurus would have starved to death after six months without scheduled feeding, but the animal actually did survive. When deprived of its normal food sources, the Mosasaurus has been confirmed to experimentally feed on unfamiliar objects; this may lead to it attempting to consume non-food items. Such behavior led to the unfortunate deaths of the Marine One personnel in June 2016.

In a deleted scene, the escaped Mosasaurus was shown tracking a pod of humpback whales (Megaptera novaeangliae). In the process of killing one, it would also have attacked and capsized a whaling ship.

Shortly after June 23, 2018, the escaped Mosasaurus was seen riding a large wave and observing multiple human surfers, homing in on one particular man. Footage cuts out just as the man falls from his board and the mosasaur’s snout breaks the surface, but it is not known if he was consumed. This is not typical hunting behavior for the Mosasaurus, but opportunistic feeding on a suddenly vulnerable prey item is far from unknown in predatory animals.

Social Behavior

Only one Mosasaurus is known to have been created, but its solitary life does not appear to cause it any distress. As a highly aggressive animal with a massive appetite, it may not have needed the company of others of its kind.


The sheer size of the Mosasaurus inhibits its ability to move on land, and even if it were smaller, it is not adapted for terrestrial locomotion at all. As a result, it and its relatives cannot crawl onto the shore to lay eggs; instead, they are believed to have given live birth in the ocean. However, the method by which Jurassic World’s Mosasaurus was reared is unknown. InGen had previously raised a Tylosaurus in an “incubation tank,” details about which are also unknown.

Female squamates, the order of reptiles which mosasaurs belong to, have a cloaca that is used as the receptive sex organ. Male squamates have two hemipenes as sex organs. Presumably, Mosasaurus would have the same kind of sex organs as all other squamates.

Due to being the only one of its kind, the Mosasaurus from Jurassic World has not bred and is unlikely to; as a result, details about its reproductive behavior are only speculative.

The mobile game Jurassic Park Builder incorrectly portrays Mosasaurus hoffmanni, a close relative, as hatching from eggs that rest on the seafloor. In real life, an air-breathing animal could not survive in an egg underwater, as eggshells are not watertight. If they were watertight, the embryo inside would suffocate.


As it is a solitary animal, most of the vocalizations made by the Mosasaurus are not communication. Instead, they appear to be involuntary sounds that it makes as it moves. When it lunges at prey, it makes a bellowing noise when its jaws open. While handling prey, it can be heard groaning and growling. It can also be heard making wailing and moaning noises after making a kill, so these presumably indicate satisfaction.

Ecological Interactions

Mosasaurus maximus is an apex predator, the largest carnivorous animal on Earth at a maximum known length of 84.9 feet. As an adult, it has no predators except for others of its own kind. As with any apex predator, its actions shape its environment.

Concept art of the Mosasaurus attacking a harpooned whale and the Yushin Maru.

When confined to the Jurassic World Lagoon, the mosasaur would have readily preyed on any other animals within its environment. It preyed on other inhabitants of Isla Nublar including Pteranodon and Indominus (causing the extinction of the latter). Smaller fish in the lagoon were later seen to be alive and well; the mosasaur preying on Pteranodons would have reduced pressure on the populations of smaller fish.

After its unintentional release from the Lagoon in June 2016, the mosasaur’s range vastly expanded. Deleted scenes demonstrate that its diet would have now included large marine mammals such as humpback whales; it also was depicted as being aggressive toward a whaling ship, which would unintentionally alleviate predatory pressure by humans on whales.

Interactions with Humans

While it was kept in the Jurassic World Lagoon, the Mosasaurus was demonstrably the biggest attraction in the park. The stadium at the Mosasaurus Feeding Show could easily house thousands of people, and on the final day of park operations the audience capacity was still at maximum. A second attraction, the Underwater Observatory, permitted visitors to view the mosasaur when it was not feeding time.

The Mosasaurus performs at a feeding show, approx. 3:00 PM 12/18/2015

The mosasaur would be fed six times every day in full view of audiences. InGen found that the mosasaur’s moderate level of intelligence enabled it to learn simple tricks, such as jumping out of the water for food. It performed this trick every two hours, though the announcer‘s dialogue suggests that it sometimes missed performances after having already eaten during a previous show. Many of the hotels and restaurants were designed with mosasaur viewing in mind, allowing visitors an excellent view of the Lagoon. Park staff recognized the possible threat that the mosasaur could pose to human life, as signs warned visitors not to enter the Lagoon and electric fencing was placed to discourage the mosasaur from accessing the Boardwalk. A visitor beach area was cordoned off near the hotels, where visitors could swim in safety.

Discarded teeth from the Mosasaurus were sold as souvenirs in Jurassic World.

During the December 18, 2015 incident, multiple Pteranodons entered the mosasaur’s habitat while squabbling over Jurassic World employee Zara Young. During the incident, the mosasaur was attracted to the commotion and consumed one Pteranodon, inadvertently swallowing Young along with it. This was the first confirmed case of the mosasaur killing a human.

Mosasaurus eye reacting to light stimulus.

Six months after the incident a team of mercenaries hired by Eli Mills at the behest of Henry Wu disturbed the mosasaur as it slept in the Lagoon, causing it to swim down and investigate the miniature submarine used by the Marine One team. This resulted in the death of the crew as it attempted to consume the minisub. Upon seeing a man climbing a ladder to a helicopter, the mosasaur’s conditioning kicked in; it performed the trick it was trained to do, leaping out of the water for a food reward. This resulted in the man’s death, the first confirmed case of the mosasaur deliberately killing a human (in the unfortunate case of Zara Young, the mosasaur was more likely targeting the larger Pteranodon).

In a deleted scene that would have taken place after this, the mosasaur was seen to follow the Japanese whaling ship Yushin Maru, consuming a whale that the ship had harpooned. In this way, the mosasaur benefited from human activity; however, it shortly thereafter capsized the ship and presumably killed the crew.

On or shortly after June 24, 2018, the mosasaur was filmed by surfers off the western coast of the Americas as it rode a large wave near shore. It was recorded approaching a male surfer, who fell off of his board while descending the wave. The footage stops just after the mosasaur’s snout can be seen breaching out of the wave; while this is not typical predatory behavior for this species, the footage certainly looks as though it is approaching the human with predatory intent. However, as the surfers’ footage stops at this point, the man’s fate is currently unknown.

Behind the Scenes

In real life, Mosasaurus maximus is considered to be a junior synonym to the smaller European Mosasaurus hoffmanni, meaning that they are the same species. The giant American species was named later than the European species, so the name of the European one becomes the scientifically correct name. Some paleontologists believe that differences in the skull features of the European and American specimens are significant enough that M. maximus should still be considered a separate valid species, and the Jurassic film franchise appears to agree with this classification and consider M. maximus to be separate from M. hoffmanni.