Allosaurus, meaning “different reptile,” is a genus of large carnivorous theropod dinosaur in the family Allosauridae. It lived during the Kimmeridgian and Tithonian ages of the late Jurassic period, approximately 155 to 145 million years ago, and is known from western North America as well as Portugal and potentially other parts of the world. The type species is A. fragilis; the species name references the fragile nature of its fossilized remains. The genus name Allosaurus describes the concave shape of its vertebrae, which was unique when the animal was first identified in 1877. However, the species that was cloned by International Genetic Technologies is now believed to be A. jimmadseni, which is named in honor of paleontologist James Henry Madsen.
The earliest fossils of Allosaurus were tail vertebrae found in the Morrison Formation of Colorado by geologist Ferdinand Vandeveer Hayden in 1869, who sent them to Joseph Leidy for study. They were variously assigned to several preexisting genera of dinosaur until paleontologist Othniel Charles Marsh named them in 1877 during the Bone Wars. Due to the intense competition between Marsh and his rival Edward Drinker Cope, many Allosaurus specimens went undescribed during the late 1870s and 1880s. In 1920, Charles W. Gilmore clarified many of Cope and Marsh’s findings and consolidated numerous fossil genera into Allosaurus. Since then, paleontologists have identified many Allosaurus fossils from the Morrison Formation, giving modern science a large body of knowledge about this animal; remains were also found in Montana, New Mexico, Oklahoma, Wyoming, South Dakota, and Utah.
While the most common species by far is Allosaurus fragilis with over seventy individuals known, there are several other species. Allosaurus europaeus was identified from the Lourinhã Formation in Portugal in 2006. In 2020 the species Allosaurus jimmadseni was identified from the Morrison Formation in older rocks than A. fragilis; aside from their age, these two can be told apart by the straight lower margin of the cheekbone on Allosaurus jimmadseni. Two other species, Allosaurus amplus and Allosaurus lucasi, are known from North America as well. Some possible remains have been reported from the Tendaguru Formation in Tanzania, though these are no longer thought to belong to Allosaurus or any allosaur. More questionable remains have been presented from Siberia and China.
International Genetic Technologies, Inc. obtained Allosaurus jimmadseni ancient DNA from blood-drinking invertebrates such as mosquitoes preserved in late Jurassic amber samples. As of 1993, the genome was 12% complete; the animal would not be cloned until the twenty-first century, at which point InGen was owned by Masrani Global Corporation. The species is identifiable based on its size and the shapes of its skull features. At the time it was cloned, it was still classified as Allosaurus fragilis.
Among the larger theropods, an adult Allosaurus may grow to around 28 feet (8.5 meters) from snout to tail and 14 feet (4.2 meters) tall when standing upright. However, some exceptional specimens may reach 34.1 feet (10.4 meters) long, which is marginally larger than the biggest known fossil specimens. An average animal weighs 1,500 pounds (700 kilograms), but when they are fully grown, they can easily be as heavy as 4,400 pounds (2,000 kilograms). At this size, it is an apex predator, and has many evolutionary adaptations to match.
The massive head (slightly wider in InGen specimens than in fossils) is distinctive, with a long snout and large nostrils giving it an excellent sense of smell; of particular note are the thin triangular horns on its head, which are sheathed in keratin and formed from the lacrimal bones. Leading to the horns are a pair of low ridges extending to the nasal bones. Fossil evidence suggests that the size and shape of the horns would vary from one animal to the next, making them easy ways to identify a particular Allosaurus. Like most theropods, it has a powerful jaw with sharp, serrated teeth; it has five teeth in each premaxilla and fourteen to seventeen teeth in each maxilla. The jaws can open impressively wide, up to ninety-two degrees, and are designed for tearing or hacking off pieces of flesh from prey. However, this means that its bite force is lesser than that of many other large theropods. Its eyes are average-sized for a theropod, with yellow sclerae and round, birdlike pupils. Like most theropods it has nictitating membranes to protect its eyes, originating from the medial canthus. Allosaurus has better-developed sinuses than more primitive theropods such as Ceratosaurus, giving it a good sense of smell. Its tongue is not particularly thick, but is pointed, and very dark blue or almost black in color.
Tough skin consisting of small scales covers the body surface of Allosaurus, and the whole body is lean and muscular. The neck is short and strong, and dorsal spines decorate much of the body’s length from neck to tail. While its forelimbs are short, as with many theropods, they are longer and far stronger than those of Tyrannosaurus and bear three-fingered hands. Each finger ends with a long curved and pointed claw, a formidable weapon in combat in addition to the powerful jaws. The thumb is the largest of the digits. It is able to pronate its wrists, as can most of InGen’s theropods, but adults are sometimes seen to hold their hands in a supinated position like their fossilized ancestors would have.
The legs, while not designed for speed to the degree that tyrannosaurs’ legs are, can still propel the animal along at speeds of 19 to 34 miles per hour (30 to 55 kilometers per hour). The main hip bone, or ilium, is massive. The legs are shorter than those of tyrannosaurs, and three of the toes bear less developed and more hoof-like claws. The fourth toe, the dewclaw, does not reach the ground; the skeleton shows signs of a fifth toe which has been lost. The tail of Allosaurus is slightly downward-sloping, and comprises about a third of the animal’s overall length.
Coloration in this species is generally subdued, as suits an ambush predator. The body is largely tan or gray, with dark blue colors on the dorsal side. Mottled gray colors may be interspersed with faded dark gray, blue, or yellow stripes; the lacrimal horns are often dull red or orange, but in at least some adult females, they are the same color as the dorsal body. Yellow rings may decorate the eye orbits of this animal and white markings may occur on the face, and the underbelly is typically a slightly lighter color than the rest of the body.
At the hatchling stage, this theropod shows a proportionally larger head than the adult, a feature that is common to many baby animals. The lacrimal horns start out quite short, elongating as the animal nears adolescence. Integument is variable and may change as the animal grows; baby allosaurs may demonstrate scaly skin, a limited coat of feathers, pebbly skin, a combination of pebbly skin and spiny quill-like protrusions, or a combination of fluff and scales.
Juvenile Allosaurus can be told apart from adults using both coloration and anatomy. In juveniles, the entire body is an ashy gray color with some darker, but very faded, mottling. The lacrimal horns are sharply pointed backward at this stage. In at least some mature females, the coloration of most of the body brightens slightly, with dark blue patterns on the dorsal side and a sandy yellow color to the rest of the body. In these mature females, the red color to the lacrimal horns is lost, becoming a dark blue color like the dorsal body. This appears to begin on the upper side of the horn, with the base of the horn staying red the longest.
Anatomical features also change with maturity. The juvenile’s body is smooth, with no distinctive features to speak of other than the lacrimal horns. In the adult, raised spines develop along the backbone from neck to tail, likely serving as display features and giving the animal a more rugged appearance. The jaw also develops, becoming more prominent, and the lacrimal horns fill out and grow to become upward-pointing. In juveniles, the legs are comparatively longer than adults.
The growth rate of this animal is not entirely known, but most of them were still juveniles in 2018. The latest they could have been cloned was late 2015, meaning adolescence is reached in a minimum of two to three years when under the effects of growth supplements. After the adolescent stage is reached, the transformation into a mature adult takes less than a year; a juvenile which escaped into the wild in the summer of 2018 was fully-grown by the spring of 2019. Fossil evidence suggests that the animals naturally reach full size in fifteen years, with a lifespan of around 22 to 28 years.
Currently, no sexual dimorphism has been identified in Allosaurus fragilis. It has been suggested that the males always retain the red coloration of the lacrimal horns, while most females lose this color, but there is no direct evidence to confirm this speculation as of yet.
An ambush predator, the Allosaurus is at home in forested areas; the deeper the forest, the more comfortable this animal will be. Its speed does allow it to do well on open plains. It has been known to voluntarily move into redwood forests, which provide it with cover as well as maneuverability. Allosaurus is commonly seen near mountainous regions, but is not known to climb far uphill; instead, it is typically seen in the valleys between mountain ranges. It can tolerate tropical climates as well as the cooler temperatures of the Pacific Northwest.
In the game Jurassic World: Evolution, the Allosaurus requires 18,900 square meters of grassland and 6,700 square meters of forest in its territory.
Allosaurus was cloned by InGen on Isla Nublar sometime before December 2015 with the intent to be exhibited in Jurassic World. However, the park closed before these animals could be successfully put on display; in the intervening time, they were maintained in habitats in Sector 5 in the island’s north.
After the 2015 incident, artificial barriers were deactivated and animals were permitted to roam the island at their leisure. Between 2015 and 2018, Allosaurus were known to roam the Western Ridge near the gondola lift as well as near Mount Sibo. On June 23, 2018, three juvenile males were sighted near Mount Sibo; one was confirmed killed when it was struck by a large piece of tephra, and the others likely perished due to the volcanic eruption or drowning. Two juvenile males, one juvenile female, and one adult were removed from the island via the S.S. Arcadia. This means that prior to the eruption, there were a total of at least seven Allosaurus on Isla Nublar, including five juvenile males, one juvenile female, and one adult of presently unconfirmed sex.
De-extinction research and development originally took place on Isla Sorna in the late 1980s and early 1990s. However, Allosaurus did not exceed 12% viability during that time. There is currently no evidence that this animal ever lived there.
During the night of June 24, 2018, three juvenile and one adult Allosaurus were transported to the Lockwood estate near Orick, California to be sold on the black market. One juvenile male (weighed at 1,115 kilograms or 1.2 tons) was sold to a currently-unknown bidder and was transported along with several other cargoes away from the estate, last seen near Monument Valley in Utah. The others, including one adult (weighed at 2,250 kilograms or 2.5 tons), a juvenile male, and a juvenile female, were released into the surrounding forest that night by Maisie Lockwood to avoid the animals dying of hydrogen cyanide inhalation.
On April 21, 2019, a female Allosaurus was confirmed to be present in Big Rock National Park in northern California. It is believed to have been one of the juveniles released from the Lockwood estate, rather than the adult. By this time, it was fully grown; as of April 22, the U.S. Department of Wildlife was tracking it with the intent to capture, along with a possible second individual (a juvenile male, if it exists). The female involved with the Big Rock incident can be identified by its blind right eye.
Behavior and Ecology
Allosaurus appears to be cathermal, active at times of day and night. At least one female released into human-occupied parts of the state of California has been seen hunting during the night, likely a means to avoid humans. This same animal has been seen active during the day when disturbed by human activity, but it appears to have a preference for nocturnal activity patterns.
Diet and Feeding Behavior
As with most theropods, the Allosaurus is a carnivore. In its native late Jurassic period, it was the apex predator in its environment, and today still maintains a competitive edge over many other predators it has been introduced alongside. The main weapons of this animal are its powerful jaws and sharp teeth, which are used to pierce the hides of prey items and tear out large pieces of flesh. If a victim survives the initial bite, it is likely to bleed out, making it easy for the allosaur to finish it off. The bite force of this animal is weaker than that of tyrannosaurs, a compensation for its ability to open its jaws astonishingly wide. On occasion, this animal may congregate in loosely-organized packs with no real authority or hierarchy to mob larger prey items.
This animal is capable of pursuit hunting, but excels at ambush, which is why it is often found in forested areas. Adults, with their proportionally shorter legs, are best suited to ambush hunting when compared to the longer-legged juveniles. Younger animals are better at chasing their prey down. Its subdued coloration helps it to avoid being seen; it will use its excellent senses of smell and hearing to locate prey, quietly move in on it, and then make a sudden attack. Since it does not rely heavily on eyesight to track prey, it can hunt quite well at night. Its ambush tactics and predatory adaptations make it one of the most efficient theropod hunters, and is is known to take down prey larger than itself. Known prey items include Nasutoceratops and possibly Gallimimus, though the latter is far faster than the allosaur and likely a difficult prey item to catch. Deleted scenes have shown it attempting to prey on juvenile Triceratops. It is a vicious brawler against even formidable foes and will weaken its enemies by wounding them. For example, an adult female allosaur was witnessed in 2019 using the talons on its toes to make gashes in the side of a Nasutoceratops, an attack which would result in blood loss and shock to the intended prey.
According to the game Jurassic Park: Operation Genesis, its favored prey species is Stegosaurus, which it would have lived alongside during prehistory. However, the species featured in this game is not A. fragilis, but rather the dubious “Allosaurus tendaguruensis,” which is now believed to be a different theropod altogether.
It is worthy of note that the Allosaurus, even as an adult, has been witnessed targeting the young of other animals rather than mature individuals when possible. An adult female Allosaurus in 2019 was observed using a loud roar to disorient and frighten a mother Nasutoceratops, causing the horned herbivore to leave its offspring temporarily unguarded. The aforementioned 2018 deleted scene would have featured a subadult allosaur targeting a young Triceratops during a stampede. In both cases, however, the allosaur was unsuccessful, as the prey’s parents intervened.
Allosaurus is a persistent predator, known to push its way through many kinds of obstacles if it believes the reward of prey is worth its struggle. It is, however, pragmatic: it recognizes when the risk to itself outweighs the reward of food, and will back down if it faces a challenge that is not worth its efforts. While Allosaurus frequently risks injury during the hunt and often sustains wounds during combat, it will not do so unnecessarily. If a prey item puts up too much of a fight, the allosaur will try its luck elsewhere.
This theropod appears to be mostly solitary, though juveniles seem to be more tolerant of company than adults. Little is known about their social behaviors, as only a few field observations have been made (and even fewer under normal conditions). The red-colored lacrimal horns of juveniles suggest a social function, especially when contrasted with the gray color of the body. Fossil evidence suggests that the lacrimal horns vary in size and shape from one animal to another, also implying that they serve social functions. In some adults (but not those portrayed in Jurassic World: Evolution), the horns of adults lose their red color; this implies that social behaviors change from adolescence to adulthood, possibly with the animals becoming increasingly solitary as they age in a manner similar to modern-day ravens.
According to the mobile application Jurassic World Facts as well as various other mobile games, the Allosaurus will on occasion form packs with its own kind for the purpose of hunting larger prey items. Despite this, it is not a naturally social animal, and these packs lack a social hierarchy or organization. They most likely disband after the hunt concludes.
The anatomical changes from adolescence to adulthood also include the formation of spikes and raised scales in all individuals. This gives the animal a more rugged and intimidating appearance, which likely serves to warn away rival allosaurs as well as competitor species.
Jurassic World: Evolution portrays the adult Allosaurus as a solitary animal, not tolerant of others of its kind. Its appearance in this game differs from the individual seen at Big Rock National Park in 2019, but its behavior appears similar. The mobile game Jurassic World Alive proposes that the differing physical appearances are the result of two distinct genetic lineages in the Allosaurus population, while sexual dimorphism has also been suggested.
All dinosaurs lay eggs to reproduce. The Allosaurus has not been observed breeding, but most likely possesses a cloaca which houses the reproductive organs of both the male and female. Cloacae have been observed in other theropod species. While the red lacrimal horns of the juvenile may be used as display features, at least some of the adult females lose the red color as they mature, suggesting that the color is not a vital function in courtship. Instead, the spines and raised scales which occur in the adult are more likely to be used to advertise maturity, fertility, and overall health to potential mates.
Theropod eggs are birdlike, being ovoid in shape, which is an evolutionary adaptation to prevent them from rolling around too much. A larger theropod such as Allosaurus would have an incubation period lasting roughly six months. Most theropods display parental care, but it is not known if both parents help to raise the young or if only one does; in any case, by the time the animal reaches adolescence, it no longer requires parental care to thrive and is able to hunt on its own.
As with many theropods, the Allosaurus cloned by InGen are most likely more vocal than their ancestors were capable of; nonetheless, they seem to have adapted well to their increased vocal capabilities. They can be heard emitting loud low-pitched bellows and deep growls to warn away threatening rivals or animals which get in their way. During hunts, an Allosaurus may suddenly roar to frighten a prey item and cause it to misstep, giving the allosaur an opportunity to attack.
Body language is also used to communicate with other species, and most likely one another. Gaping the jaws and assuming a threatening position can be used as an intimidation tactic, while an irked allosaur may shove or snap at other animals to warn them away. While it has not been directly observed, body features such as the lacrimal horns are most likely used for communication, such as identifying a particular allosaur.
Despite its aggressively predatory nature, the Allosaurus can live alongside a wide variety of other animal species. Many of its neighbors on Isla Nublar between 2015 and 2018 included animals that it would naturally have encountered during the Jurassic period, such as Apatosaurus, Brachiosaurus, and Stegosaurus. There is significant fossil evidence suggesting it preyed upon the latter, though sauropods are likely too big for a single allosaur to kill.
Other herbivorous animals in its territories on Isla Nublar included the hadrosaurs Parasaurolophus and (prior to its extinction) Edmontosaurus as well as the pachycephalosaurs Stygimoloch and Pachycephalosaurus, which would have been suitable prey. The heavily-armored Ankylosaurus would have presented more of a challenge, as would the fleet-of-foot omnivore Gallimimus and the tiny, elusive Microceratus. Several species of ceratopsians are known to live in similar territories to Allosaurus, including Triceratops, Sinoceratops, Nasutoceratops, and possibly Pachyrhinosaurus. The juveniles of these horned herbivores are known to be potential prey for Allosaurus, though the adults present it with a challenge that it may not be able to overcome. When it preys upon any of these animals, the allosaur acts as a regulator for their populations, which in turn benefits the plant life in its territory. This permits the allosaur’s feeding grounds to grow denser forests and undergrowth, which the allosaur benefits from.
This animal has been known to live alongside many carnivorous species as well. Potential competitors include Carnotaurus and Tyrannosaurus, which were most likely its biggest threats; it would have lived near the smaller Metriacanthosaurus on Isla Nublar before that species became extinct. It also lived alongside fish-eating Baryonyx and the pterosaur Pteranodon; since Allosaurus seldom feeds on fish, it would not have had difficulty coexisting with these animals. It is large enough that Velociraptor is not a major threat, especially as raptors have become exceedingly rare due to human intervention. The Compsognathus is one of the smallest de-extinct theropods, and while it can be found in the same areas as Allosaurus, it is unlikely to ever be more than a nuisance to adult allosaurs.
While allosaurs are tolerant of other animals inhabiting their territories, their lives as neighbors are often less than harmonious. Other than hunting and killing animals in the areas surrounding their homes, Allosaurus can become defensive of their personal space and will attack and chase away other animals when stressed. During the 2018 eruption of Mount Sibo, a juvenile Allosaurus was seen snapping at a Gallimimus which had run too close during a stampede and giving an aggressive display to a gyrosphere. (In the original cut of the film, the Gallimimus accidentally bumps into the allosaur and is roughly shoved aside in response; for unknown reasons, this was changed so that the animals do not make physical contact in the scene.)
In the Jurassic period, Allosaurus was affected by hematophagous pests such as early mosquitoes, which is how InGen was able to obtain its DNA. No studies have currently been performed to determine whether modern mosquitoes affect it in a similar way.
The game Jurassic World: Evolution portrays it as being somewhat tolerant of other animals, and as being a host for the bacterium Campylobacter which may cause campylobacteriosis. This bacterium is known to affect up to 100% of certain poultry populations.
Relationship to Humans
InGen originally intended to exhibit Allosaurus in Jurassic Park, but by 1993 had not reconstructed enough of its genome to bring viability past 12%. The animal got a second chance in the twenty-first century with Jurassic World, but none of them are known to have been put on exhibit by the time the park closed in late 2015. At the time, all of the allosaurs appear to have been juveniles. At least one reached maturity by 2018, and a second was fully mature by 2019.
Allosaurus was among the less propagandized species during the 2017-2018 Mount Sibo controversy, with relatively little mention of it by the Dinosaur Protection Group. It was featured in at least one piece of promotional artwork in which it was used to illustrate the idea of many dinosaur species living in harmony. This animal was targeted by mercenary Ken Wheatley, who was hired by Eli Mills at the behest of former InGen geneticist Henry Wu; four of these animals including one adult and three juveniles were captured from Isla Nublar before June 23, 2018. This makes it one of the most heavily targeted large theropods.
During the subsequent black-market auction at the Lockwood estate, a juvenile male allosaur was sold to a currently unknown buyer for roughly US $11,000,000. The other three animals were later threatened by hydrogen cyanide leaking into the estate’s sub-basement. In order to save them from the lethal chemical, Maisie Lockwood released the animals into the wild. One of the juvenile female allosaurs settled into Big Rock National Park about twenty miles away from the estate, living relatively near a mated pair of Nasutoceratops which also survived the incident.
On April 21, 2019, several months after the Lockwood incident, the now-mature female was involved with another incident at the park in which it attempted to hunt the Nasutoceratops pair’s offspring and also threatened a family of campers. The animal was driven away from the campers by being shot in the right side of the face with a double crossbow, but lingered around the area the following day while the U.S. Department of Wildlife attempted to track it down. News reporter Rebecca Ryan attempted to report on the Big Rock incident but was unable to complete her report when an allosaur (potentially a second individual, as it appeared to be a juvenile male and had both eyes intact) was chased through the area by a USDW helicopter. Her news van’s driver is believed to have died during these events.
Based on Jurassic World: Evolution, the cost for raising an Allosaurus from fertilization to maturity as of 2018 would be $1,873,000.
Behind the Scenes
Adult and juvenile Allosaurus were apparently designed for the film Jurassic World: Fallen Kingdom, but ultimately only the juveniles appeared. An adult is known to have existed, since the S.S. Arcadia‘s manifest can be seen to have two Allosaurus on it: one which is said to be a juvenile and one which, like the other adult dinosaurs, is not. According to members of the Universal Studios design team, the allosaurs appearing in Jurassic World: Fallen Kingdom were the male design, with a separate female design not appearing in the film.
The body of the allosaur designs used in the films was allegedly based on the common species Allosaurus fragilis, but the skull anatomy was based on Allosaurus jimmadseni (which was, at the time, classified as A. fragilis). Because the skull anatomy is the primary means of differentiating these two species, Jurassic-Pedia has chosen to classify the species appearing in the films as A. jimmadseni.
Director Colin Trevorrow has stated that the Allosaurus which appears in the 2019 short film Battle at Big Rock is a female, and is the matured form of one of the juvenile allosaurs which escaped the Lockwood estate at the end of Jurassic World: Fallen Kingdom. Its design was noticeably changed, making it appear different from the established appearance of adult allosaurs shown in Jurassic World: Evolution in 2018. The allosaur in the Jurassic World motion comic is depicted with the design of the males from Jurassic World: Fallen Kingdom; it also lacks the blind right eye of the one seen in the short film. Jurassic-Pedia considers the possibility that there were two allosaurs present in Big Rock National Park, but acknowledges that the motion comic lacked proper management and that an error is also likely.
Auctioned Allosaurus – male individual sold as a subadult on the black market in 2018
Allosaurus – Big Rock National Park – female individual transplanted to the Pacific Northwest