Stegosaurus is a genus of very large thyreophoran dinosaur in the family Stegosauridae, which is named after this animal. Its name means “roofed reptile” in reference to its dorsal plates; paleontologists originally assumed that these lay flat on its back, forming a kind of armored roof. The specific epithet of this particular species, S. stenops, means “narrow face.” This animal originally lived in the late Jurassic period, between 155 and 150 million years ago, and inhabited what is now western North America. Because InGen specimens bred for the company’s de-extinction theme parks have shown an ability to grow noticeably larger than their fossil counterparts, Jurassic-Pedia differentiates them from their ancestors using a subspecific epithet, gigas, meaning “giant.”
Fossilized remains of Stegosaurus were first discovered north of Morrison, Colorado in 1877 and were described by Othniel C. Marsh. He assigned them to a species he named Stegosaurus armatus, which he believed was a large turtle-like reptile; what are now known to have been upright dorsal plates were then thought to be armor resembling a shingled roof. An abundance of Stegosaurus remains were uncovered over the next few years, and Marsh named a second species S. ungulatus in 1879. Over the years, Marsh described a large number of Stegosaurus discoveries, and in 1886 he named three new species, including the subject of this article S. stenops as well as S. duplex and S. sulcatus. The species described in this article was found at Garden Park by Marshall P. Felch and named the following year. By 1891, Marsh realized that the armor of this creature did not lie flat, but was upright; he positioned them in a single row, but found this arrangement impossible since this would cause the plates to overlap.
The known species were joined in 1901 by a new addition, Stegosaurus marshi, which was described by Frederick Lucas. In the early 1900s, Lucas also revisited older stegosaur discoveries and found that their anatomy was different from Marsh’s assumptions. Lucas’s research set the groundwork for our modern understanding of Stegosaurus, including reconstructions commissioned to legendary paleoartist Charles R. Knight.
Today, there are three species of Stegosaurus known to science. The best-known, the type species since 2013, is S. stenops; a great many fossils of this animal have been found and it is one of the most abundant of the stegosaurs. It can be distinguished by its broad and proportionally large dorsal plates, while the plates of the tail are smaller and rounded. This species is smaller than other known stegosaurs, at 23 feet (7 meters) in length. The largest species is S. ungulatus at 29.5 feet (9 meters), and can be told apart by its smaller, pointier plates; it also has flat spine-shaped plates just before its thagomizer, as well as longer legs. The third species, S. sulcatus, is distinguishable based on its unique huge furrowed spikes; based on their large bases, these may have been attached at the shoulders or hips rather than being part of the thagomizer.
Stegosaurus stenops, easily identified by its plate shape, was cloned by International Genetic Technologies, Inc. at the Site B facilities on Isla Sorna using ancient DNA recovered from Jurassic amber inclusions sometime in the 1980s or early 1990s. As of June 11, 1993, InGen had engineered up to Version 2.035 of Stegosaurus. This species persists today after decades of captive breeding, and can now be found on the North American mainland.
While fossil animals reach only 23 feet in length, genetic tampering at InGen has yielded far larger animals. InGen Stegosaurus routinely grow to lengths of 30 to 40 feet (9.1 to 12.2 meters) and measure 19 feet (5.8 meters) to the tip of the tallest plate, and exceptional specimens can grow to an enormous 55 feet (16.8 meters) long. Fossil Stegosaurus are estimated by paleontologists to have weighed 5.8 to 7.7 U.S. short tons (5.3 to 7 metric tons). The Jurassic World website advertises its stegosaurs at a five-ton weight for a thirty-foot animal, meaning that its specimens are proportionally lighter in weight than their fossil ancestors, but since they grow to a much larger size they are heavier anyway.
The head of Stegosaurus is famously small, making up only a tiny amount of its body size. Its skull is long and narrow, with a keratinous and toothless beak; these features demonstrate evolution in favor of browsing among low-growing vegetation. Some InGen stegosaurs bred for Jurassic World feature skin covering the surface of the beak, hiding it from view; this skin is absent in those stegosaurs bred during the 1980s and 1990s, as well as some of the Jurassic World stegosaurs. While there is no evidence for such a covering of skin in the fossil record for stegosaurids, it is known from hadrosaurids. Stegosaurus has teeth behind its beak; fossils show small, flat triangular teeth, though in InGen’s stegosaurs, these teeth are larger and rectangular rather than triangular, making them similar to mammalian molars. In both prehistoric and modern Stegosaurus, though, the teeth are built for grinding. Today’s Stegosaurus have fleshy cheeks similar to those found in many ornithischian dinosaurs, but there is debate as to whether the beak of the prehistoric Stegosaurus left any room for cheeks. Fossils show that, in prehistory, this animal would have had pebbly ossicles on the underside of its head, which InGen’s specimens lack; the neck is also shorter in these cloned versions. The nostrils and eyes are both small, with the eyes possessing round, birdlike pupils and dark orange sclerae. Its tongue is short, pink, flat, and not especially muscular.
Stegosaurus has a famously small brain, similar in size to that of a domestic cat and shaped like a rounded cylinder. This is exceptionally small for a dinosaur; a five-ton adult Stegosaurus has a brain weighing only 2.8 ounces (80 grams). This makes Stegosaurus less intelligent than many other dinosaur species; however, its nervous system was sophisticated enough, with features such as the glycogen body near the hips used to maneuver the tail. The size and shape of this neurological feature led to it being mistaken for an auxiliary brain, a misconception popularized in the media due to the potential for jokes about the animal having a second brain in its rear. In reality, Stegosaurus, like all known vertebrate animals, has only one brain, located in the head. Glycogen bodies are known in most other dinosaurs, including birds.
The neck is not terribly long, but the shoulder blade is robust, and the overall body is shaped a bit like a teardrop with a high back and low-hanging head. Like all but the most primitive stegosaurs, it is a quadruped, capable of only briefly rearing onto its hind legs. Its front limbs are shorter and thinner than its hind limbs, and the toes end in rounded claws. There are five toes on each front foot, with the inner two being blunt and hoof-like in the fossil record but not particularly notable in InGen specimens. While fossils show three-toed hind feet, InGen Stegosaurus have one extra toe for a total of four on each foot. To support the feet, Stegosaurus has pads behind its toes. Its anatomy means it is not speedy; it reaches its maximum speed at about 4.3 miles per hour (7 kilometers per hour), as running much faster than this would cause its hind legs to overstep its front legs.
Of course, the most obvious and recognizable feature of this animal is its dorsal armor. This comes in the form of two rows of bony plates in staggered formation, increasing in size toward the hips and decreasing in size toward the head and tail. The largest plates in thirty-foot adults are three feet (91.4 centimeters) tall and about as wide. There are between seventeen and twenty-two plates, with twenty-two appearing to be the most common number, and evenly paired plates being much more common than asymmetrical numbers. In Stegosaurus stenops, these plates are close to pentagonal in shape, with the larger ones pointing slightly backward. These plates are highly modified osteoderms, similar to the tough scaly armor of crocodiles, and are covered with a vascularized keratin sheath. This feature allows the plates to be used for thermoregulation, as cool air passing over them decreases the blood temperature within. Plates on Stegosaurus are chiral; that is, the left and right plates are not exact mirror images of one another, similar to the left and right hands of a human. Also like a human’s hands, a Stegosaurus can show dominance in one set of plates versus the other, with either the left or right row leading. There is currently no research to determine whether the side of the leading plate row influences which way the Stegosaurus looks when aiming its tail. In the wild, no two plates on this animal look quite the same, but in the laboratory a greater degree of regularity can be achieved.
After the dorsal plates, the most famous feature of Stegosaurus is its tail, which is long and flexible, ending with a structure called a thagomizer. This consists of four conical spikes, which protrude horizontally at slight upward angles from the tail. Unlike the staggered pattern of the plates, the spikes of the thagomizer are positioned precisely opposite one another in two pairs. Each spike is about as long as the animal’s tallest dorsal plate. A stegosaur’s thagomizer is its main weapon against predators, and thanks to the tail’s strong muscles and flexibility, it can be swung at thirty feet (9.1 meters) to forty meters (131.2 feet) per second. The tail is normally held well off the ground, but is flexible. While InGen’s original specimens faithfully replicate this position from their fossil ancestors, later specimens show lower-hanging tails that droop down, sometimes swinging low enough to touch the ground. It is unknown whether this was an intentional alteration or a health defect, though claims in Jurassic World: The Game that InGen had reconstructed the complete Stegosaurus genome by 2015 would suggest the latter.
This animal’s coloration is simple but variable, with dull forest or olive greens being the most dominant color. Some animals demonstrate a more vivid shade, while dusty yellow-greens and stony gray-greens are also known. The plates tend to be darker than the body, with some animals showing brown or reddish tints, and some having light-and-dark horizontal banding. Patterning may be as simple as the color fading from green to yellow across the body, or may include dark splotches or vertical stripes. At least one variant was genetically engineered for Jurassic World to display violet-blue bioluminescence, which manifested over most of the body including the plates.
Juvenile Stegosaurus can be easily told apart from adults by more than just size. The size and shape of its body armor changes as the animal ages. When it first hatches, the plates and spikes are small rounded nubs, along with other typical features of baby animals such as a disproportionately large head and shorter tail. Growth patterns differ between InGen’s original stock of Stegosaurus and the newer stock bred for Jurassic World.
In the original stock, the thagomizer grows faster than the plates, with its spikes reaching full size by the time the animal is an adolescent. The plates do not reach their full size or final pentagonal shape until full adulthood, suggesting that they play a role in advertising maturity in Stegosaurus of this breed. Even adolescents and subadults can be seen to have more rounded plates than the mature adults.
In newer stock, the reverse is the case. Plates are fully-formed by the end of the juvenile stage, becoming proportionally similar to those of the adult. Because the plates grow from small bony nubs to full-sized pentagons before the dinosaur grows out of the juvenile stage, young animals of similar body size may show either developed or undeveloped plates. The thagomizer is a bit slower to grow, but reaches its full proportions not long after. The reason for this is unknown, but it suggests that the plates play a different social role in newer Stegosaurus, with other cues to advertise maturity taking their place.
In both variants, coloration remains consistent throughout the animal’s life. Claims have been made that it sheds its plates as it grows and replaces old plates with new larger ones, but no Stegosaurus has ever been seen with less than full-sized plates, so this claim is assumed to be incorrect. Fossils also demonstrate that the plates grow with the rest of the skeleton, rather than being replaced periodically. Stegosaurus has been known to rub its plates against trees while growing, similar to Triceratops with its horns. While it was claimed in 2016 that this behavior was intended to hasten the plate-shedding process, the similar behavior in Triceratops is used to help shed merely the outer keratinous layer surrounding the horns. Therefore, the idea that Stegosaurus sheds its plates is almost certainly a misconception, and only the keratin exterior is shed. The bony plate itself remains attached unless broken off by an accident.
While some paleontologists have suggested that the dorsal plates of Stegosaurus and its relatives may have been sexually dimorphic, this is not yet confirmed by scientific research. These theories suggest that the males’ plates are broader while the females’ are taller. However, InGen stegosaurs do not appear to demonstrate this kind of dimorphism. While males and females of the original breed have been positively identified, there are few easily noticeable differences that can be used to sex the animals. Newer breeds of Stegosaurus have not been explored thoroughly either, making it impossible to sex them based on casual observation alone, though the difference in color patterns has been suggested to be related to sexual dimorphism.
This animal prefers forested environments, since this is where its food sources are most plentiful, and denser vegetation offers it shelter from the elements as well as larger predators. Its bulk allows it to push through undergrowth efficiently, toppling smaller trees that get in its way and crushing shrubs and low growth. Stegosaurus has been seen in both coniferous and angiosperm forests. It feeds mainly on the ferns found in dense woodland. However, it can also survive in more open areas, and has been sighted on grasslands and in brush, as well as at least one animal having been sighted in an arid mountainous region. It seems to avoid marine coasts, as it is a poor swimmer, and prefers warm environments as opposed to cold ones. At least one Stegosaurus released into the Pacific Northwest migrated south between the early summer of 2018 and late spring of 2019, indicating that these animals can migrate quite far in search of suitable habitat.
Fossil evidence suggests that the best habitat for this animal would be a semi-arid flatland with wet and dry seasons. In the Jurassic period, it inhabited prairies and floodplains with gallery forests along the riverbanks, where it would probably go to feed, drink, and find shelter. Plant life known to exist in its ancient habitat includes tree ferns and cycads, Araucaria conifers, and ginkgoes.
In the game Jurassic World: Evolution, it requires 13,700 square meters of grassland and 11,100 square meters of forest in its territory to make a suitable habitat.
Stegosaurus was one of fifteen species originally intended to be exhibited at Jurassic Park on Isla Nublar. By the summer of 1993, Version 2.035 Stegosaurus embryos were in storage at the park facility, but no live animals had been introduced. They were intended to be housed in a paddock in the central part of the island, visible from the main tour road which bordered it on the south and east, separated from it by a concrete moat. It was also separated using a concrete moat from a service road to the north. This paddock bordered the Jungle River to the west and southwest, and the Jurassic Park Aviary to the northwest. Aside from the Aviary, the Stegosaurus habitat did not directly border any other animal paddocks.
Due to the failure of Jurassic Park in mid-1993, Stegosaurus did not reach Isla Nublar until late 2004 or early 2005. During that time, surviving animals from Isla Sorna were imported to stock the upcoming theme park, Jurassic World. This species was not yet present on the island by September 2004 and was not among the eight species on display when the park opened on May 30, 2005, but fairly quickly became a staple at the new park. It was introduced to Gyrosphere Valley, and was able to venture as far as the Jungle River, meaning its range spanned Sectors 4 and 6. There were also stegosaurs in Sector 5, with some being members of Herd M.
Like the other dinosaurs, this species was actively bred in Jurassic World, with new animals hatching regularly from the Hammond Creation Lab. Once they reached the juvenile stage, they would be introduced to the Gentle Giants Petting Zoo until they were deemed ready for introduction to the paddocks. As of December 22, 2015, there was one Stegosaurus in the petting zoo, with fully-developed plates and larger body size indicating that it was nearly adolescent.
By late 2015, the stegosaur population was healthy and sustainable. Along with the juvenile in the petting zoo, there were at least eighteen adults and one young juvenile in Gyrosphere Valley, as well as two adults and one subadult living near the Jungle River. Fourteen adults were also sighted near Camp Cretaceous on December 19 of that year, members of Herd M; these included at least four striped, three spotted, and three plain animals. They would have grazed during the day, and inhabited nighttime paddocks when not outside. Also living in Sector 5 were the genetically-engineered bioluminescent stegosaurs; it is not known how many of these were created. Unlike the bioluminescent Parasaurolophus, these were not integrated into a park attraction. Six adult Stegosaurus were kept in a Sector 4 veterinary station for undisclosed medical conditions as of December 22.
Jurassic World experienced a severe safety incident on December 22, 2015 which caused its permanent closure, leaving the Stegosaurus and other dinosaurs to fend for themselves. Those in the veterinary station were abandoned, though all but one were fortunately released on December 24 by Camp Cretaceous attendees who became stranded on the island. Two of the stegosaurs moved north and probably joined Herd M; the others probably moved into the valley. While conditions were too hazardous to release the last animal at the time, it is likely that the campers later returned to free the final dinosaur. Much of the population appears to have originally converged on Gyrosphere Valley, where the bulk of the animals already lived. At least two bioluminescent stegosaurs survived into June 2016, with an adult female and young juvenile being sighted together in the island’s northern forests. The juvenile’s presence suggests that the stegosaurs may have been breeding.
As time went on, the population diverged, with some favoring the forests near Camp Cretaceous and Mount Sibo while others migrated to the farthest south of Isla Nublar, near the Ferry Landing docks. By January 15, 2016, at least two were even living in the harbor building, having utilized the maintenance tunnels to reach it. It is unknown what became of the adolescent from the petting zoo. By June 23, 2018, there were at least nine and possibly as many as fifteen adult Stegosaurus living near Mount Sibo’s eastern foothills, while the carcass of a fifty-five-foot-long animal was found to the volcano’s south. It appeared to be recently deceased. None of the animals sighted here were those from Herd M, nor were they the bioluminescent stegosaurs, which may have died out as they could not efficiently hide from predators. Other than this, the stegosaur population appears to have suffered less than some of the other dinosaurs on the island. Assuming that the southern herd was around the size of the northern one, there could have been around thirty stegosaurs living on Isla Nublar by the summer of 2018, only a small decrease from the nearly forty confirmed there in 2015.
On June 23 that year, Mount Sibo violently erupted after months of buildup, driving the stegosaur herd along with the other dinosaurs away from the volcano. Most were killed in the eruption, either due to suffocation, injury from volcanic debris, or drowning in the ocean. Any that survived would have eventually died as their food sources were eliminated. Six adults were captured by mercenaries led by Ken Wheatley, with at least one being taken from the northern population, and removed from Isla Nublar via the S.S. Arcadia. The northern stegosaur was measured at 5,950 kilograms (6.6 U.S. short tons) at the time of loading, making it a reasonable weight for a mid-sized InGen specimen. It was cosigned by Adam Tate and logged into the ship’s manifest at 13:50, held in Container #33-1021-2042 (Cargo #72362).
Due to the eruption of Mount Sibo, it is most likely that Stegosaurus is extinct on Isla Nublar.
This dinosaur was originally bred in the Embryonics facility on Isla Sorna, where InGen performed its research and development in the 1980s and 1990s. The date at which the first Stegosaurus was cloned is not known, but it was sometime between 1986 and mid-1993. For undisclosed reasons, this animal was not considered ready for exhibition at Jurassic Park by 1993, and so was left on Isla Sorna. When the island was struck by Hurricane Clarissa in 1995, the facilities were abandoned and the animals were turned out into the wild. As of 1993, there were eleven Stegosaurus confirmed living on Isla Sorna.
Stegosaurus has been spotted in both eastern and western Isla Sorna, though this may represent migratory patterns rather than separate populations. In February of 1997, breeding was recorded in the island’s northwestern regions in a coniferous forest south of the game trail. A family unit consisting of a mated pair, a subadult, and a juvenile female was sighted on February 21, with a similar group with one additional adult being sighted not far away (this was possibly the same group, though the young juvenile was only sighted on one of those occasions). Nesting grounds were reported by Dr. Sarah Harding in the preceding days, suggesting that the stegosaurs had recently bred, but that the infant mortality rate was fairly high.
One adult male and one juvenile, possibly members of this herd, were captured by the InGen Harvester expedition led by Peter Ludlow, but were released by animal rights activist Nick Van Owen during the night of February 21, from which point they most likely returned from the Harvester camp to their home.
A herd of nine animals, including two young juveniles, was sighted around midday on February 23 in the north-central part of the island, some miles inland from the beach. This herd, again, may have included the members of the herd seen on February 21, though these locations are fairly far apart. There could have been between fourteen and nineteen Stegosaurus on Isla Sorna at that time.
In the summer of 2001, stegosaurs were sighted in the island’s western region, with at least two being reported by Eric Kirby near the safe house in June or July. A herd of fifteen animals was sighted in the western grassland near the airstrip on July 18, including two younger juveniles and three subadults, while a smaller herd on the central peninsula the following day included four adults and one older juvenile. These numbers imply a population of at least fifteen to twenty-two Stegosaurus. If the animals seen in the west were not the same as those seen in the east four years prior, there could have been as many as forty-one stegosaurs on Isla Sorna by 2001, a large increase from the original eleven animals in 1993.
As could be expected, the population increase had drastic effects on Isla Sorna, and by 2004 the populations of most of its dinosaurs were in decline. Competition for food grew fierce, and some animals began to die off. The well-protected Stegosaurus may have fared well during these trying times, but by late 2004 or early 2005, the surviving animals were captured by InGen Security under the direction of Masrani Global Corporation and shipped to Isla Nublar. Supposedly, there are no dinosaurs remaining on Isla Sorna today, though some evidence of continued activity has been reported.
While Stegosaurus was among the dinosaurs planned to be exhibited in Jurassic Park: San Diego in 1997, neither animal was successfully transported there. As a result, the first confirmed case of a Stegosaurus on the mainland was the 2018 incident at the Lockwood Estate in Orick, California. During these events, six adult stegosaurs from Isla Nublar were illegally transported to the manor to be sold on the black market by Eli Mills, working at the behest of Henry Wu. One of these animals was sold to an unknown buyer, and its location has not yet been determined. The other five were held overnight on June 24, but were released by Maisie Lockwood in order to save them from a hydrogen cyanide gas leak.
Since their escape into the forests of the Pacific Northwest, some of these stegosaurs have been spotted in the wild. One was filmed by park rangers at an undisclosed location probably in California sometime during June or July of 2018. A Stegosaurus was also sighted on the Angeles Crest Highway near the famous tunnels on May 10, 2019. This second sighting is about 720 miles southeast of Orick, meaning that the animal migrated this distance over the course of around 320 days (or roughly 2.25 miles per day), a respectable feat for this slow-moving creature.
Behavior and Ecology
Stegosaurus is diurnal, meaning it is active during daylight hours. It feeds during the morning and evening, and generally rests around the heat of midday. Activity has been reported during the night, but this is uncommon and usually the result of human interference. Even after a year of living on the North American mainland, wild Stegosaurus do not appear to have adjusted their lifestyle, though it is possible that they will change their behavior patterns with more time.
Diet and Feeding Behavior
This animal is a herbivore and spends the bulk of its free time eating. The head of Stegosaurus is built low to the ground, and its beaked jaws are capable of only up-and-down motion. Its teeth differ from those of its ancestors, being molariform rather than peg-shaped, but are still designed for grinding food. It is possible that the modification of its teeth may have been intentional on the part of InGen’s geneticists as a way to ensure Stegosaurus could get all the food it needs to survive, since the fossil record provides surprisingly few clues as to how this animal sustained itself in its own time.
Its anatomy means that it normally can only feed on low-growing plants, with ferns being perhaps the most notable staple in its diet. It can reach plants growing around three feet off the ground, though if it is able to rear up, it can feed from trees. Stegosaurus is believed to also feed on mosses, conifer cones and other fruits, and cycads. According to Jurassic World: Evolution, its preferred food is paw paws, but it also enjoys mosses and cycads, while it cannot digest horsetails, palms, or rotten wood. However, it is able to consume live woody plants. It is probably not adapted to chew grass on its own, but its genetic modifications may have enabled it to eat this common food source in its new, modern habitat. Stegosaurus is known to feed on the bracken fern, which can cause bracken poisoning if consumed in excess. In prehistory, this dinosaur lived in and near forests with ginkgoes and Auracaria trees; today, it has been known to make its home among redwoods. Coniferous trees probably provide it with food. In 1997, it was confirmed to frequently feed on lysine-rich plants such as soy and agama beans to compensate for its genetically-engineered lysine deficiency.
There is currently no fossil evidence of Stegosaurus using gastroliths, despite its inability to chew; it is unknown if it makes use of gastroliths in the modern day in S/F canon, though it is confirmed to do so in C/N canon.
This stegosaurid is a social herd animal, though some solitary individuals have been seen. They chiefly form family units with members of their own kind, and herds in the wild will often consist of mated pairs and their offspring. Young may remain with their parents into the subadult or even adult stage, with the older adults taking the lead. These older adults are more likely to be familiar with the reliable food sources and predictable threats of their local area, as well as being familiar with migratory routes.
Although it forms herds, Stegosaurus is unintelligent and has fairly few ways to socialize. These mostly consist of keeping in close physical proximity to their friends and family. When they travel, the subadults and juveniles will stick close to the adults, either their parents or whichever adults they have imprinted on. The distinctive plates of Stegosaurus probably help it recognize its own kind; this is supported by paleontological evidence, since different species of Stegosaurus have differently-shaped plates. Taking this a step further, members of the same species have subtle differences in the shapes and arrangements of their own plates, which suggests that Stegosaurus can recognize individual members of its herd. This animal also has a number of vocalizations that it uses while traveling or feeding, which ensure that different members of the herd know where their fellows are.
Despite its low intelligence, social bonds among Stegosaurus are reasonably strong, and they will work together to fend off threats to their young. If a predator is spotted, the stegosaurs will coordinate their movements to surround the predator, cutting off its movements. While a lone stegosaur is quite capable of defending itself, working with their herd members makes them an impenetrable force; not even the largest theropods will attempt to attack a whole herd if it stands together. If they manage to drive away or kill a threat, the herd will also retreat from the area as one, not leaving any of their fellows behind. Herds will fan out when they are relaxed, but travel in single file when wary; when actively fleeing a threat, the adults will flank the juveniles to keep them safe.
Competition for dominance in herds is mostly non-violent, with rough shoving being as far as they will go. When two animals compete for control of a territory, they will make shows of strength by swinging their tails at one another, never actually striking. To demonstrate their strength, they may swat rocks and other objects through the air, with a farther throw or a heavier object clearly showing which competitor is the more powerful.
According to Jurassic World: Evolution, this dinosaur forms social groups of between five and nine animals, becoming stressed if it is too lonely or overcrowded. Lone stegosaurs have been seen in the wild, but they have exhibited heightened levels of aggression.
The large dorsal plates of Stegosaurus are probably used in courtship, since they are its most obvious physical features. The strong, flexible tail with its four bony spikes may also be used to court mates, as a more powerful tail is a desirable survival trait. Stegosaurus has never been observed mating, leaving much speculation as to how it mates with such ornamentation on its body. Most dinosaurs have a cloaca which houses the reproductive organs, and Stegosaurus is probably no exception. Mated pairs may remain together for years and breed multiple times throughout their lives.
This dinosaur appears to breed during the winter months, since mid-sized juveniles appearing a few months old have been encountered in late winter to midsummer. In Costa Rica, the rainy season lasts from May to November, with November to May being the dry season. If Stegosaurus juveniles in the wild have grown to around eight feet in length by February to June, then it stands to reason that the eggs hatch some months earlier than this, during the late rainy season. Eggs of dinosaurs this size normally incubate for six months to a year, though the duration for Stegosaurus eggs in particular is not known.
Even though it is not an intelligent dinosaur, Stegosaurus is known to be quite a good parent. This was discovered in February 1997 by Dr. Sarah Harding, who studied the behavior and family dynamics of a Stegosaurus herd on Isla Sorna. She found that the nesting site showed signs of having been heavily used by both adults and juveniles, despite the eggs having hatched some time ago, suggesting that the parents remain in the nesting site for long periods of time. At least two juveniles, and at most four, were observed on the island on three separate occasions during the span of the next three days, always with adults present. The relatively small number of juveniles suggests a high infant mortality rate, making it even more important for the parents to care for their offspring.
Dr. Harding observed a multigenerational herd on Isla Sorna during this time, including a pair-bond and offspring from at least two breeding seasons. Offspring appear to remain with their parents for many years, and can sometimes still be seen living alongside them as subadults or adults. At this age, they can help care for their younger siblings, assisting their parents in driving off predators.
Like most InGen dinosaurs, these Stegosaurus are often treated with growth-boosting hormone supplements to accelerate their maturation. Their natural growth rate is not known, but fossil evidence suggests that it would be slower than some other stegosaurs. Some of the stegosaurs bred before 1993 were adults by 1997, and some subadults which were bred probably around 1993 were also observed. This implies that some Stegosaurus reach adult size in four or five years. As they grow, their plates and spikes are delayed in development compared to the rest of the skeleton. Younger stegosaurs have small plates and spikes, which begin to take on their adult shapes during adolescence. In some of InGen’s original stegosaurs, subadults were still developing their plates, while in more recent animals the plates are fully-formed during adolescence. Fossil evidence suggests that the plates begin to grow more rapidly once skeletal maturity is reached. Sexual maturity probably follows this, with the fully-developed plates advertising that the animal is ready to breed.
Befitting a less intelligent dinosaur, this creature’s communication methods are fairly simple. It largely vocalizes with grunts and hoots. These are often heard while groups of Stegosaurus travel together, and appear to be a way to ensure that the herd stays together. If one has wandered away, the vocalizations of its kin will summon it back. They are also heard making similar noises while eating, which can similarly keep the herd as a cohesive unit while foraging for food. Though these sounds are not complex, they can help to reaffirm social bonds.
Juveniles are small and generally quieter than the adults, which makes sense, since they are more vulnerable to predators. However, they can be quite loud when they are frightened, emitting yowls and groans which alert the adults. When a juvenile emits these sounds, all the adults nearby will immediately respond with an aggressive display toward any potential threat they see, and will not stop until they believe it to be neutralized. An angered adult Stegosaurus can produce a bull-like bellow to intimidate enemies, which is often heard when the animal is charging. A similar sound is produced by angered Triceratops and Parasaurolophus, suggesting that it is a convergent behavior.
Along with vocalizations, this animal probably uses visual cues to communicate. Its high dorsal plates are its most noticeable feature, making it appear larger when viewed from the side and easily helping Stegosaurus identify one another. When fleeing a threat, adults will flank the juveniles to protect them; when in this position, the tall bodies and plates of the adults create a kind of living corridor that the juveniles know to remain inside. This helps them recognize the adults as a source of safety. It is likely that body language involving plate display and tail movement are used in a variety of situations by Stegosaurus.
This is one of the biggest armored herbivores, with its tall dorsal plates making it stand out among other species. It will tolerate other herbivorous neighbors, but mostly those which do not compete with it for food; this dinosaur’s aggression levels vary from low to moderate, and it can be somewhat territorial and cantankerous in the wild. Those in captivity tend to be calmer and friendlier, but this behavior quickly changes once they are no longer actively cared for. It may tolerate other stegosaurs (the game Jurassic Park: Operation Genesis describes Kentrosaurus as its favored companion), but so far none have been cloned in the film canon.
On Isla Sorna, when this animal was first observed in the wild, it was known to inhabit coniferous forests including coast redwood trees. These trees are too large for an average Stegosaurus to damage, but they probably fed on the cones. Stegosaurus can push over smaller trees, and the large size of its body means that it will crush and topple plant life as it moves through woodland. It mainly feeds on plant that grow low to the ground, such as ferns and cycads. In 1997, these dinosaurs were observed living in areas near herds of Parasaurolophus, Pachycephalosaurus, Gallimimus, and Mamenchisaurus. However, these species tended to live on the game trail, rather than in the wooded areas nearby. This, and the differing food sources preferred by these dinosaurs, meant that they did not compete with Stegosaurus for food, and they interacted fairly little. Its relationship to the ceratopsian Triceratops is less understood. However, since these two herbivores (along with Parasaurolophus) share an aggression cry, it is possible they interact with each other. Trikes can be territorial, especially toward the young of other species, making them a potential competitor and threat.
Carnivores may attempt to prey on Stegosaurus, as on Isla Sorna it shared overlapping territory with the island’s apex predator Tyrannosaurus rex. This large theropod is likely the only animal which would have threatened an adult Stegosaurus at the time, with powerful crushing jaws that could overcome the stegosaur’s bony armor. To defend itself, Stegosaurus brings its spiked tail into play, swinging it at high speeds and using the thagomizer to puncture skin, muscle, and even bone. A wound from these three-foot spikes can be devastating, and Stegosaurus strikes with reasonable accuracy and can pivot around on its front limbs while looking over its shoulder to aim. It does not necessarily try to kill its foes, rather intending to drive them back before fleeing. Living in herds is another defense against predators; not even a Tyrannosaurus would dare attack a whole herd of Stegosaurus on alert.
An adult seen in 1997 showed scarring on its flank consistent with Velociraptor attack, suggesting that these smaller carnivores may also come into conflict with Stegosaurus. It is more likely that they try to prey on the juveniles, and the adults fight them off. When fighting a smaller predator, Stegosaurus can still use its tail, but may opt to simply crush the offending animal under its multi-ton weight. It also shares territory with Pteranodon, which could be a threat to juveniles as it is known to prey on young dinosaurs. The fragile and lightweight body of Pteranodon compared to the might of an adult Stegosaurus means that this pterosaur would have to rely on its agility in the air to avoid being trampled or struck by a thagomizer.
Smaller dinosaurs may use the mass of Stegosaurus for protection. Some have been seen with bird droppings among their plates, suggesting that birds may sometimes roost there. This would be beneficial to both parties, since the birds are protected from predators, and may eat parasites such as ticks off of the stegosaur. Other small dinosaurs such as Compsognathus are known from stegosaur territories, but their relationship to the stegosaurs is largely not researched. The stegosaurs at least produce copious amounts of dung that the compies can eat, allowing them to obtain nutrients that they could not find in their own carnivorous diet. Compies also eat flies, including mosquitoes, which at least bit stegosaurs during prehistory; this is how InGen was able to obtain its DNA. It is not known whether modern mosquitoes can feed on stegosaur blood.
By 2001, the dinosaur population of Isla Sorna grew, and new species appeared. Stegosaurus came into more regular contact with other species, forcing this reclusive animal to interact with its neighbors more often. Along with the familiar Triceratops and Parasaurolophus, it was observed living alongside Corythosaurus, Brachiosaurus, and Ankylosaurus. New predators in its territories included Ceratosaurus and the huge semi-aquatic Spinosaurus, though neither of them have been confirmed attempting to prey on Stegosaurus.
The situation on Isla Nublar was similarly crowded, with Stegosaurus being integrated into habitats containing many familiar species. It also encountered at least three herbivores it is not known to have lived alongside on Isla Sorna: Edmontosaurus, Microceratus, and Apatosaurus. Eventually, this number grew to include upcoming new species such as Sinoceratops. For the most part, Jurassic World’s park rangers kept the peace between these varying dinosaur species, but Stegosaurus does not seem to have gotten particularly attached to its neighbors. For example, on December 21, 2015, a stegosaur in Herd M panicked during a thunderstorm and struck an Ankylosaurus with its thagomizer by accident, showing no signs of recognizing its mistake. The ankylosaur was uninjured thanks to its heavy armor, but this incident nonetheless increased tension in Herd M that eventually led to a stampede.
Once released into the wild, they also encountered Stygimoloch and Peloroplites. Their relationships with these other herbivores are not well understood. New carnivores, such as Allosaurus, Baryonyx, Carnotaurus, and Teratophoneus, also became a part of their ecosystem; those living near the Jungle River would have encountered more Baryonyx as well as the Suchomimus and Metriacanthosaurus.
Most of these carnivores do not seem to have bothered the herd-dwelling and impressively defensive Stegosaurus. Unlike many dinosaurs, whose populations decreased dramatically following the closure of Jurassic World, the Stegosaurus herds remained mostly consistent in size. However, no juveniles were seen any later than June 2016, suggesting that while the adults could defend themselves, they were failing to breed. No evidence for predation on adults has been confirmed; however, the carcass of a huge individual showed signs of scavenging from the many carnivores on Isla Nublar at the time.
Though it is mightily defended, Stegosaurus is susceptible to disease, which can be spread by small pests such as mosquitoes and ticks as discussed above. However, according to Jurassic World: Evolution, this animal is at least unaffected by the common cold.
Relationship to Humans
Although Stegosaurus was successfully bred by InGen by 1993 and was planned to appear in Jurassic Park, none were shipped by Isla Nublar before a series of incidents prevented the park from opening. Had it been a success, Stegosaurus would have been visible from both the main tour and the Jungle River Cruise. Already, this dinosaur was featured on merchandise for the park, which capitalized on the immense popularity of Stegosaurus.
This is easily one of the most famous and recognizable dinosaurs, making it highly marketable, and it appears in numerous museums, films, video games, and comics. Toys of Stegosaurus are quite common. Due to its popularity, InGen selected it as one of several herbivorous dinosaur species meant to feature in the resurrected Jurassic Park: San Diego in 1997, which would have housed one adult male and one juvenile female. These plans were intentionally sabotaged, meaning that once again Stegosaurus failed to reach its intended park destination. It was finally put on display for the public in Jurassic World, with the Isla Sorna population being shipped to Isla Nublar as originally intended.
While in the park, this dinosaur was housed in three locations: two were accessible to the public, the Gyrosphere attraction and the Cretaceous Cruise. A third group of Stegosaurus was kept in Sector 5’s Herd M, a research subject that benefited the overall park. Juveniles, bred in the Hammond Creation Lab, were kept in the Gentle Giants Petting Zoo until they were deemed old enough to live in the paddock areas. Genetic engineering yielded new versions of this animal, and they flourished on the island. By 2015, a new breed had been engineered by Dr. Henry Wu to exhibit bioluminescence by incorporating DNA from a local species of algae. The CEO of Masrani Global Corporation, Simon Masrani, had drafted up plans to put bioluminescent dinosaurs on parade down Main Street during the night. These plans were ultimately scrapped due to the impracticality of organizing and cleaning up after this event, so the bioluminescent stegosaurs were housed in Sector 5 on their own and were never shown to the public.
This dinosaur is territorial and cantankerous, and when stressed can easily become a threat to humans. It is large enough to be dangerous when aggressive, but not so large that it can safely ignore human-sized animals; if it feels that its space is being invaded, or that its offspring are possibly under threat, it will attack to trample or impale the offending human. As with many territorial dinosaurs, it interprets a high-pitched whistle as a challenge and will also attack if whistled at. On the other hand, it differs from some dinosaurs (such as Brachiosaurus) in that it will ignore attempts by humans to mimic its own vocalizations. Whether this is because humans cannot sufficiently mimic its sounds, or because it is not intelligent enough to realize that the human is attempting to communicate, is not known. During Jurassic World’s ten years of operation, no major incidents with Stegosaurus were reported, suggesting that this simple-minded creature was one of the park’s more unproblematic inhabitants. This is likely due to the comforts of captivity; with their needs met and their offspring never threatened by predators, captive stegosaurs have lower stress levels and so are less likely to attack. This can lead to people believing the dinosaurs are friendly, but realistically, only professionals should handle such a large and powerful creature.
While they remained a popular attraction featured in numerous Jurassic World advertisements and merchandise, they did not quite reach the levels of stardom that Tyrannosaurus and Triceratops enjoyed. Still, they are the favorite dinosaur of many people, including the Hammond Foundation’s Cabot Finch.
Jurassic World closed its doors in late 2015 due to a highly-publicized security incident. These animals came under threat from volcanic activity during 2017 and 2018, with a cataclysmic eruption on June 23 causing the localized extinction of most of Isla Nublar’s wildlife (both modern and de-extinct). Throughout the preceding months, the Dinosaur Protection Group lobbied to have the dinosaurs including Stegosaurus rescued, and frequently used images of this animal to further the cause. This species’s easily recognizable profile and popularity with children was surely one of the reasons it so often appeared in their material.
While both government and corporate entities rejected the proposed rescue mission to Isla Nublar, the operation was financed and carried out illegally by the Lockwood Foundation. Several adult stegosaurs were removed from the island after being captured by head mercenary hunter Ken Wheatley, who was employed by the Foundation’s manager Eli Mills. Wheatley notably took a tooth from one of the last stegosaurs as a trophy, though he viewed his quarry with a kind of malicious glee and delighted in causing it to suffer. The whole operation was in fact corrupt, and the animals were taken to the Lockwood estate to be sold on the black market. One Stegosaurus was sold at around the halfway point, selling to bidder #187 for US $17,000,000. During the night, the others were threatened by a hydrogen cyanide gas leak and were released into the wild by Maisie Lockwood to save their lives. The location and status of the sold individual is unknown.
Since their release into the wild, Stegosaurus have been involved in a few incidents with human interaction. In the days following the incident at the Lockwood estate, park rangers in a nearby area followed a Stegosaurus which eventually turned to chase them away. On May 10, 2019, people were watching a Stegosaurus wandering along the Angeles Crest Highway near its tunnels when a 2015 Subaru Forester WRX emerged from a tunnel at high speed. The stegosaur, already stressed from being crowded by the humans and separated from its own kind, swung its tail as the vehicle swerved to avoid it, causing the vehicle to fall over the edge of a cliff.
Based on Jurassic World: Evolution, the cost for raising a Stegosaurus from fertilization to maturity as of 2018 would be $320,000.
Behind the Scenes
Originally, Stegosaurus was planned to appear in the film Jurassic Park like its novel counterpart, but this role was eventually given to Triceratops instead. After numerous fan requests, Steven Spielberg agreed to include Stegosaurus in the sequel, The Lost World: Jurassic Park, where it played a notable role. This is in contrast to the novel, which features only a single Stegosaurus for a brief scene. A regular favorite, Stegosaurus has gone on to appear in virtually all Jurassic media since 1997.
Claire – female seen as a juvenile in 1997