Mosasaurus maximus (S/F)

mosasaurus-detail-headerMosasaurus maximus is an extremely large species of marine mosasaur. Its genus name means “Meuse River lizard,” referring to the place it was first found. This reptile 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 belongs 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.


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. (A 2019 social media infographic released by Universal Studios lists 21.9 meters, or 71.9 feet.) However, its size in 2018 appears to have increased immensely, reaching around 120 feet. Weight estimates have also varied; Jurassic World social media has listed it at 28 or 29 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. The DPG has given a 30-ton weight estimate as of June 8, 2018; as the mosasaur has grown enormously larger than any of the given lengths, it is likely heavier than any of these estimates as of 2018 as well.

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

Notably, the 70- to 80-foot lengths this animal reached when in captivity would already make it the largest carnivorous vertebrate ever known, though some planktivorous whales such as the blue whale were still larger. It was also exceeded in length by some of the largest sauropod dinosaurs. 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, called the pterygoid 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. The mosasaur’s nostrils are located about halfway down its snout, on the dorsal surface rather than the front or sides. This would mean it breathes at the surface similarly to a whale. The skull itself is very long, consisting mostly of the jaws, and tapers to a rounded point. Its eyes have yellow sclerae and round, black pupils.

Left eye of an adult female Mosasaurus reacting to light stimulus

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, so this is most likely the case in Mosasaurus as well.

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 directly, but a LEGO version of the infant makes an appearance in the animated series Legend of Isla Nublar. It is depicted as essentially a smaller version of the adult, with the fins and head proportionally larger and with noticeable dark stripes which are highly faded in the adult. Its body color is overall darker in this depiction of the infant stage.

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 22, 2015 and June 2016, its listed length increased by 12.7 feet; if these measurements are accurate, its 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 and pterygoid teeth.

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. It has been known to inhabit waters where the lower temperature range is around 54 degrees Fahrenheit (in the oceans near New Zealand), but the actual extent of its cold tolerance is not currently known. At adult size, it requires a habitat containing about three million gallons of salt water. To prevent waste accumulation, this water must be circulated out, necessitating a large outflow system (Jurassic World used a partially overland and partially underground canal system to accomplish this).

The mosasaur’s original habitat, like that of most de-extinct species, was vastly different from the environment it must inhabit today. As a result, Dr. Henry Wu had to alter certain genes to allow its survival in the modern world, as with many other animals. As of late August 2004, he was working on acclimatizing the genome to the waters of Isla Nublar, but the exact nature of the modifications made remains undisclosed.

Mosasaurus maximus is highly migratory and constantly moves around the ocean in search of adequate food sources. Between June 2016 and sometime following June 2018, the only known mosasaur had traveled from Isla Nublar to O’ahu (4,798 miles northwest); by 2019, it was sighted off the coast of New Zealand (4,000 to 5,000 miles southwest of O’ahu). This, however, is far from the longest distance traveled by a marine reptile: a leatherback sea turtle (Dermochelys coriacea) was recorded traveling over 12,000 miles (19,312 kilometers) in 647 days, and females of this species regularly make journeys of 6,000 miles (9,656 kilometers) or more when traveling from feeding grounds to nesting grounds. Mosasaurus maximus appears to travel shorter distances in the same amount of time, likely expending more energy in active hunts than in long-distance travel.

Isla Nublar

A single female Mosasaurus maximus was bred on Isla Nublar for exhibition in Jurassic World. 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 22, 2015. During this time, it was restricted in its movements by security systems in place in the Lagoon. It was kept in the Lagoon’s western half, unable to move into the shallower eastern half due to a security fence bordering the monorail track. If need be, it could be restricted from the area nearest Main Street by a secondary fence, but this was not usually in place during normal park operations. It is known to have been raised at some point shortly following the 2015 incident, as it was still in the raised position in 2018.

After the park was shut down, the security systems in place around the Lagoon began to break down due to neglect and the harsh weather of the Central American wet season. Within six months, the monorail and fencing system in the Lagoon had suffered serious damage; once the fence had been broken enough, the mosasaur would have had access to both halves of the Lagoon. Due to its huge size, it could potentially have sped up the destruction of these artificial barriers using its strength.

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. By 2018, it had migrated westward into the Pacific, away from Isla Nublar.

Isla Sorna

While the Muertes Archipelago is certainly within the mosasaur’s ideal range and on the way to its 2018 location in the Hawaiian Archipelago, there is no evidence that the only known individual ever remained there for any period of time.

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 off the northern coast of O’ahu, Hawaii on or shortly after June 25, 2018. Roughly one year after this, it was filmed off the coast of New Zealand.

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. When left to its own devices, it appears to hunt primarily during the day. When at rest, it floats in the water column rather than directly on the surface, likely rising up to breathe.

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 12/22/2015 as one of its last prepared meals, and the Jurassic World website indicates that sharks were its typical food items. Some media has portrayed it as feeding on live sharks that were apparently introduced to its habitat; these would likely have supplemented its diet during times when the feeding show was not operational. Mosasaurus tracks prey using sight, smell, and sensing vibrations including sound. Noise carries much farther underwater, making this a useful way to find live food.

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, Isla Nublar (12/22/2015)

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 pterygoid teeth prevent 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. It only eats when it is hungry, like most animals, and does not appear to store food for later, since it did not return to eat the rest of the Indominus. Animals killed in defense of its territory may be eaten even if it was not hunting at the time.

The Mosasaurus exhibits the first known case of ambush-feeding on a terrestrial prey item, Isla Nublar (12/22/2015)

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.

Sometime after June 25, 2018, the escaped Mosasaurus was seen riding large waves and observing multiple human surfers. Eyewitnesses suggest that one particular surfer was eaten after falling from his board; a second surfer was attacked via ambush shortly after. 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. In 2019, boaters near New Zealand filmed one ambushing a great white shark (Carcharodon carcharias) while the shark itself was in the process of capturing a New Zealand fur seal (Arctocephalus forsteri); both the fish and mammal were consumed by the mosasaur. Similarly to the case of Zara Young, the consumption of the fur seal was likely unintended, but not unwelcome.

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 need or want the company of others.


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. However, fossil eggs discovered in Antarctica in 2020 have suggested the possibility that, like some modern reptiles, mosasaurs may have laid vestigial leathery eggs that hatched immediately.


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, or noises it makes to comfort itself. 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, but also while confronting intruders in its territory; these are presumably used to threaten competitors.

Since only one has been cloned thus far, it is unknown how they would communicate with each other, but they probably would rely on visual signalling methods.

Ecological Interactions

Mosasaurus maximus is an apex predator, the largest carnivorous animal on Earth at a maximum confirmed length of 84.9 feet (though long-lived healthy animals may grow much larger). As an adult, it has no predators except for others of its own kind. As with any apex predator, its actions shape its environment. It is territorial, confronting and investigating intruders in its domain by circling them at the surface. This gives it the opportunity to observe its potential rival or prey from both above and below the water.

Concept art of the Mosasaurus attacking a harpooned humpback whale and the Yūshin 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.

Relationship to Humans

While it was kept in the Jurassic World Lagoon, the Mosasaurus was demonstrably one of the biggest attractions 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 12/22/2015

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 22, 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.

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 later, the mosasaur was seen to follow the Japanese whaling vessel Yūshin 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, which presumably resulted in the deaths of most or all of the crew.

On or after June 25, 2018, the mosasaur was filmed by surfers off the northern coast of O’ahu as it rode large waves near a surf break. 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; eyewitness accounts suggest the surfer was eaten. It was recorded shortly afterward attempting to eat a second surfer, prompting the evacuation of the beach.

In 2019, boaters off the New Zealand coast filming great white sharks also recorded footage of the mosasaur ambushing and consuming a great white shark which had itself just captured a fur seal. Having secured much larger prey, it is unlikely that the mosasaur had intent to attack or eat humans in the area. In fact, it most likely preys almost exclusively on animals considerably larger than human beings; it has only been confirmed to have killed two humans (one of which was unintentional). Other deaths are suspected, but unconfirmed.

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.

The mosasaur’s design was, at one point, going to incorporate a forked tongue like that of modern monitor lizards, which are its closest living relatives. However, Jurassic World‘s design team opted not to do so, believing that this would make the mosasaur look like too much of a fantasy animal (particularly when combined with its already-exaggerated size).

Notable Individuals

Jurassic World Mosasaurus – female individual bred for Jurassic World

Disambiguation Links

Mosasaurus (IDW-JPR)