Kentrosaurus

Type Species: Kentrosaurus aethiopicus

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae

Time Period: Late Jurassic 

Location: Africa

Diet: Herbivore

The African stegosaur Kentrosaurus was closely related to Stegosaurus though it was half its size, clocking in at around fifteen feet in length. Kentrosaurus had a small, elongated head with a beak that it used to sever tough plant material to be digested in its barrel-like gut. Its skin was covered in bony osteoderms, and it had small plates on its neck. These small plates were dwarfed by the plates that ran along its back in a series of fifteen rows. These plates were elongated with a thickened section in the middle, as if they were modified spines, and they were probably covered in horn. These plates gradually merged into spikes on the hip and tail. The longest spikes were on the end of its tail, and it would’ve used its thagomizer as a defensive weapon. It also had a long spike on each shoulder. Because the thigh bones come in two different types, it’s likely that males and females differed in their stoutness (a case of sexual dimorphism). 

Kentrosaurus is considered a low-browsing herbivore, and it likely roamed the thick conifer forests of northern Africa’s inland woodlands and may have even browsed on foliage in the less-lush coastal regions. If it ate while on all fours, it could reach up to five and a half feet off the ground; if it was capable of rearing back on its hind legs to eat, it could access food up to eleven feet off the ground. As a low-browser, it would’ve shared its niche with the iguanodont Dysalotosaurus, leaving the higher foliage to macronarian sauropods such as Giraffatitan. 

Kentrosaurus shared its environment with predators such as Elaphrosaurus, Allosaurus, and Veterupristisaurus. The former was too small to pose any real threat, but Allosaurus and Veterupristisaurus were a different story. The forty-foot-long Veterupristisaurus was the top predator in its environment, and it’s likely that Kentrosaurus would’ve faced-off with this predator on numerous occasions, and those plates and spikes would’ve come in good use. Scientists estimate that it could swing its tail up to speeds of 30 miles per hour, and continuous rapid swings wouldn’t only discourage attacks but could deal massive damage as the spikes ripped open its attackers’ skin, punctured its soft tissues, and broke ribs or facial bones. Repeated blows could even fracture the sturdy limb bones of the stoutest predator. With its ability to pivot quickly round on its hind legs, it would be adept at keeping its spikes pointed towards the attacker. If Kentrosaurus were a herding animal, the family group may have ‘circled-the-wagons’ with their tail spikes facing out to ward off curious predators. Such a wall of spikes would be virtually impenetrable and would likely be enough to discourage even a pack of hungry Allosaurus. Some scientists speculate that a lone Kentrosaurus, when under attack, might have charged backwards, using its tail spines like a spear, much in the manner of modern porcupines. 

Alcovasaurus

Type Species: Alcovasaurus longispinus

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae – Dacentrurinae

Time Period: Late Jurassic

Location: North America

Diet: Herbivore

The North American stegosaur Alcovasaurus grew up to eighteen feet in length; this medium-sized stegosaur would’ve been a low browser in prehistoric North America. Its main enemies would’ve included the theropods Allosaurus, Torvosaurus, and perhaps Ceratosaurus. Much of Alcovasaurus’ anatomy is unknown, but because what we do know is similar to the African Kentrosaurus, most reconstructions make it similar to its African contemporary. Alcovasaurus was originally identified as a species of Stegosaurus. This classification was questioned, however, due to five significant anatomical differences, not least its long dermal spikes. Alcovasaurus had two tail spike pairs as its thagomizer that were slender and elongated and ninety percent of the thighbone length. Some scientists argued that these larger spike pairs weren’t indicative of a different species but of sexual dimorphism used for display; perhaps, the argument went, male stegosaurs had flashier thagomizers. Other scientists argued that this stegosaur was less closely related to Stegosaurus and had more affinity with the African Kentrosaurus. Serious studies of this dispute were hampered when the type specimen was damaged by water after a pipe burst at the University of Wyoming; studies couldn’t continue until more specimens were recovered. Recently those scientists who argued for Alcovasaurus being a different genera won out, and Alcovasaurus is now differentiated from its contemporary Stegosaurus.

Miragaia

Type Species: Miragaia longicollum

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae – Dacentrurinae

Time Period: Late Jurassic 

Location: Europe 

Diet: Herbivore

The stegosaur Miragaia was closely related to its contemporary cousin Dacentrurus. Miragaia could grow eighteen to twenty feet in length and would clock in at around two tons. Paired triangular plates ran down the midline of its neck; these plates were asymmetrical with a convex outer side and a concave inner side. They were obtuse but lightly hooked at the front. A long, narrow, and straight spike has been preserved; some paleontologists believe this was a shoulder-spike seen in some stegosaurs, but others believe it was part of the tail. Miragaia’s tail anatomy isn’t known, but it’s usually reconstructed with a four-spiked thagomizer like that seen in its near relatives. Because Miragaia’s front limbs were almost as high as the rear limbs, its overall posture was more horizontally level to the ground than what we find in most other stegosaurs, whose bodies slope down to the ground so that their heads were better situated for low browsing.

Miragaia is noteworthy for its elongated neck, which was built by seventeen vertebrae. It had the longest neck of any known stegosaur, and most scientists believe this represents the pinnacle of a trend toward longer necks in stegosaurs. Thyreophorans – the dinosaur clade to which stegosaurs belong – originally had nine neck vertebrae, and one of the most basal stegosaurs, the Chinese Huayangosaurus of the Middle Jurassic, had nine, as well. While more advanced stegosaurs such as Stegosaurus had twelve or thirteen vertebrae, Miragaia outdoes them – and it even outdoes most sauropods of its time. Only a few Chinese sauropods – such as Euhelopus, Mamenchisaurus, and Omeisaurus – had as many neck vertebrae as Miragaia; most sauropods of the Late Jurassic had only twelve to fifteen widely-spaced vertebrae. Scientists have come up with two explanations for Miragaia’s elongated neck. The first holds that it developed due to sexual selection: if longer-necked stegosaurs of this species were seen as more attractive, then it makes sense that necks would get longer over time. Another theory, and one which is more likely, is that the long neck developed as an aide to niche partitioning. Miragaia lived alongside the obviously low-browsing Dacentrurus (and Stegosaurus may have even ocean-hopped to reside in Portugal); because of this, these two species would be in direct confrontation. Niche partitioners coexist by eating different foods, and it may be that Miragaia evolved as a medium-browser, able to reach foods inaccessible to other stegosaurs. Its limb structure, which indicates a shift away from a low-browsing stance, supports this theory for the origin of Miragaia’s long neck. 

Hesperosuchus

a mother Hesperosaurus defends its child against an Allosaurus

Type Species: Hesperosaurus mjosi  

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae

Time Period: Late Jurassic 

Location: United States 

Diet: Herbivore

The infamous Stegosaurus wasn’t the only stegosaur roaming the Morrison during the Kimmeridgian; its slightly smaller cousin Hesperosaurus was present, too (though it was likely more closely related to Dacentrurus of Europe). Hesperosaurus grew up to twenty to twenty-two feet in length – making it slightly smaller than Stegosaurus, which could grow up to thirty feet long – and weighed two to three tons. Like Stegosaurus it had two rows of plates running along its back; asymmetrical bases imply that the rows were staggered rather than symmetrical. Hesperosaurus’ plates were wider than those of Stegosaurus but not as tall, and its skull was deeper than that of its Morrison kin. Like Stegosaurus, Hesperosaurus had a four-spiked thagomizer on its tail; the front pair was thicker than the latter pair, and the latter were more horizontally directed towards the rear. Hesperosaurus’ tail spikes angled slightly backwards, pointing away from the body, implying that they were used in defense against predators such as Allosaurus and Torvosaurus. At least one Allosaurus specimen shows damage to its vertebrae that seems delivered by a stegosaur’s tail spike. 

CAT-scans on Hesperosaurus’ plates show that they had thin but dense outer walls and were filled with thick but spongy bone. This bone shows signs of being remodeled during the growth process. The plate bones were supplied with blood via long and wide arterial vessels. CAT-scans of the tail spikes show that they have thicker walls than the plates, and the interior spongy hollows are smaller. Each spike had a single artery that ran along the longitudinal axis. Skin impressions from Hesperosaurus give us a glimpse of what it looked like enfleshed: a part of the lower flank preserves rows of small, hexagonal, non-overlapping convex scales; higher on the flank are rosette structures with large central scales. Impressions of the back plates show no scales but a smooth surface with low parallel ridges; these likely represent the horn sheath covering the plate, and if so, these represent the first direct proof of such plate sheaths in stegosaurs. The horn sheath on the plates indicate that they had a defensive function, as the horn layer would not only strengthen the bony plate but give it sharp cutting edges. Simultaneously, the display function seems plausible, as these plates would likely be brightly colored in real life. Horn sheaths are a blow to those who believe the plates served a thermoregulatory function, as the sheaths would’ve hampered the plates’ ability to thermoregulate; however, the theory cannot be wholly rejected, for some cattle and ducks use horns and beaks to dump excess heat despite horn coverings. 

Yingshanosaurus

Type Species: Yingshanosaurus jichuanensis

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae – Stegosaurinae 

Time Period: Late Jurassic

Location: China 

Diet: Herbivore   

The Chinese stegosaur Yingshanosaurus was on the smaller side of things, growing to about sixteen feet snout-to-thagomizer, and it’s known for a pair of broad, wing-like spines on its shoulders that were flat like the bony plates on its back. These shoulder spines had large, flat, trapezoidal bases; after a sudden kink, they were reduced to a more narrow straight shaft that remained flat but with a protruding ridge on the outer side. The plates on its back were small and relatively low, and they were triangular or fin-shaped. The largest plates were only about five inches high and seven and a half inches long. These plates were uniformly flat with a rough, veined surface. As a low browser, Yingshanosaurus plodded through the Jurassic forests of prehistoric China munching on cycads and ferns. 

Dacentrurus

Type Species: Dacentrurus armatus

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae – Dacentrurinae

Time Period: Late Jurassic

Location: Europe 

Diet: Herbivore   

The stegosaur Dacentrurus was initially discovered in England, though fragmentary remains have been found in France, Spain, and Portugal (in which fossilized eggs are attributed to Dacentrurus), indicating a wide distribution among the islands and archipelagos of northeastern Laurasia. We know that stegosaurs were regularly attacked by large theropods in North America (Stegosaurus and Allosaurus had a long-running feud), and it’s believed that Dacentrurus faced similar opposition on its own turf; however, the precise identity of its larger theropod assailants is unknown, as the larger European theropods of the Jurassic date back to the Early and Middle Jurassic (such as Dubreuillosaurus and Poekilopleuron). If the Oxfordian theropod Metriacanthosaurus continued into the Kimmeridgian, it's likely it and Dacentrurus duked it out a time or two. This stegosaur was initially named Omosaurus, but since that name had already been given to a species of extinct crocodile, the name was changed to Dacentrurus.

a Dacentrurus defends against a Ceratosaurus (never mind these two likely didn't coexist!)

Dacentrurus was a large, heavily-built stegosaur that grew up to thirty-two feet in length and clocked in around five and a half tons. It had a broad gut and a massive rump. Its hind-limbs were short, but the forelimbs were long; thus Dacentrurus had the same general proportions as its North American cousin Stegosaurus, though their ‘plate armor’ was different. Dacentrurus had eight pairs of triangular plates that ran from the neck to the end of the hip; these ‘double-rowed’ plates were followed by four pairs of large spikes that ran down to the thagomizer. Dacentrurus’ stagomizer consisted of four more pairs of spikes that pointed to the side, and these tail spikes had sharp cutting edges on the front and rear sides. The arrangement of ‘plate and spike’ armor is reminiscent of its African cousin Kentrosaurus. Though Dacentrurus is often portrayed with a spike growing near the shoulder, this is artistic license based upon the fact that many primitive stegosaurs – i.e. those that had a mix of both plates and spikes – employed such shoulder spikes. 

Tuojiangosaurus

Type Species: Tuojiangosaurus multispinus

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae 

Time Period: Late Jurassic

Location: China

Diet: Herbivore 

The Chinese stegosaur Tuojiangosaurus was discovered in the Shaximiao Formation of China. This bone-bed dates back to the Oxfordian stage of the Late Jurassic, and this stegosaur is one of three stegosaurs found in the environment (the other two are Chialingosaurus and Chungkingosaurus). Contemporaries of Tuojiangosaurus included sauropods such as Mamenchisaurus and Shunosaurus, theropods such as Yangchuanosaurus and Gasosaurus, and ornithischians such as the early ornithopod Agilisaurus and a heterodontosaur holdout from the earlier Jurassic known as Tianyulong. 

Tuojiangosaurus is the best understood Chinese stegosaur. It was medium-sized at twenty-three long and six and a half feet tall. Its weight has been estimated to nearly three tons. It had a narrow and low head, bulky body, and short limbs. It had at least twenty-five teeth, and these teeth had a thick base that merged at the inside into a triangular vertical median ridge. Tuojiangosaurus had two rows of plates along its spine; these became taller over the hip region. Those at the neck and front trunk were rounded or pear-shaped, while the plates towards the rear became more triangular and pointed. All the plates had a thickened central section, as if they were modified spikes. Tuojiangosaurus seems to have had seventeen pairs of these plates and spikes. 

The thagomizer at the end of its tail consisted of two outward-pointing robust spikes on each end of the tail. These were angled at 45 degrees towards the vertical, indicating they were used for defensive purposes. The plates wouldn’t have been any protection against predators, as they’re too weak and brittle to protect against a powerful bite. Because they’re not adapted enough for thermoregulation purposes, it seems the best explanation towards their purpose is that of inter-species display. Many stegosaur species coexisted, and recognizing one’s own kind would’ve been aided by particular arrangements and shapes of plates between species. 

the shoulder spikes on this Tuojiangosaurus are hypothetical, based on the fact that
many primitive stegosaurs - and its contemporaries - had shoulder spikes. None were found
with the remains we have.

Gigantspinosaurus

Type Species: Gigantspinosaurus sichuanensis

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria 

Time Period: Late Jurassic

Location: China

Diet: Herbivore 

The Chinese stegosaur Gigantspinosaurus lived in the Oxfordian stage of the Late Jurassic. It was small-sized, reaching fourteen feet snout-to-tail and weighing 1500 pounds. It’s distinctive appearance consists of relatively small dorsal plates – a testament to its primitive, basal placement within stegosauria – and extremely large shoulder spines, even larger than those of the later African Kentrosaurus. These shoulder spines were twice the length of the shoulder blades on which they rested. The plates on the neck are small and triangular, and the head would’ve been relatively large with thirty teeth in the lower jaws. Its hips were broad and narrow, its forelimbs were robust, and the low neural spines of the four sacral vertebrae and the first tail vertebra were fused into a single plate. Scutes were discovered among the remains, but their placement on the body is unknown. Skin impressions show rosettes with a central pentagonal or hexagonal scale surrounded by thirteen to fourteen ridged smaller square, pentagonal or hexagonal scales. Gigantspinosaurus was a low browser that likely fed on ferns and cycads. 

Chungkingosaurus

Type Species: Chungkingosaurus jiangbeiensis

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Huayangosauridae 

Time Period: Late Jurassic

Location: China

Diet: Herbivore 

The stegosaur Chungkingosaurus was discovered in the Shaximiao Formation of China. This bone-bed dates back to the Oxfordian stage of the Late Jurassic, and this stegosaur is one of three stegosaurs found in the environment (the other two are Chialingosaurus and Tuojiangosaurus; some believe Chialingosaurus and Chungkingosaurus are the same animal). Contemporaries of Chungkingosaurus included sauropods such as Mamenchisaurus and Shunosaurus, theropods such as Yangchuanosaurus and Gasosaurus, and ornithischians such as the early ornithopod Agilisaurus and a heterodontosaur holdout from the earlier Jurassic known as Tianyulong. 

Two Chungkingosaurus specimens have been found; both were adults, with one thirteen feet long and the other sixteen and a half feet long. This could be a matter of sexual dimorphism, though stegosaurs have traditionally been interpreted as loners (though some stegosaurs may have traveled in small family groups). Chungkingosaurus resembled in many ways its larger contemporary Tuojiangosaurus, which lived in the same environment. Subtle differences between the two include the fact that Chungkingosaurus was smaller, had a deeper snout and front lower jaws (resulting in a high, narrow skull), and non-overlapping teeth with less pronounced denticles. Chungkingosaurus’ hips and humerus are more primitive than more derived stegosaurs. The deep skull may be a relict of a primitive trait or an adaptation for supporting stronger muscles for eating tougher vegetation. This stegosaur had two rows of plates and spikes on its back; they were arranged in pairs, but the total number is unknown (though most scientists believe it had fourteen rows of plates). Its plates were thickened in the middle, as if they were modified spikes, and they resemble those of Tuojiangosaurus. The thagomizer – the tail spikes used as a defensive weapon – are known only from one specimen. Its thagomizer consisted of two pairs of obliquely vertical stout spikes. It may have had a third pair towards the front of the back two pairs that was present when the specimen was discovered but lost during the excavation. A unique feature of its thagomizer was an additional pair of spikes at the very end of the tail; these were long, thin spikes oriented horizontally, giving the full thagomizer a ‘pin-cushion’ spike array. 

Chialingosaurus

Type Species: Chialingosaurus kuani

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Stegosauridae 

Time Period: Late Jurassic

Location: China

Diet: Herbivore 

The stegosaur Chialingosaurus is known from a single specimen that includes a partial skeleton (but no skull); the fossilized remnants include six vertebrae, the coracoids, the humeri, a right radius, and three spines. It was found in the Shaximiao Formation in China, and is one of three stegosaurs known from the environment. The other stegosaurs are Chungkingosaurus and Tuojiangosaurus. Some scientists believe Chialingosaurus and Chungkingosaurus are actually the same genera, rendering the stegosaur count of Shaximiao to two. Contemporaries of Chialingosaurus included sauropods such as Mamenchisaurus and Shunosaurus, theropods such as Yangchuanosaurus and Gasosaurus, and ornithischians such as the early ornithopod Agilisaurus and a heterodontosaur holdout from the earlier Jurassic known as Tianyulong. Chialingosaurus was a small and slender stegosaur that reached only about thirteen feet in length. Like all stegosaurs it was a low browser, likely munching on ferns and cycads. Reconstructions of Chialangosaurus’ armor is guesswork, but it have generally been modeled after Kentrosaurus. Some paleontologists believe that the arrangement of the spines on the hip and tail – and possibly the shoulders – would’ve been used both for defense against predators and as a means of display, differentiating this genera from the similarly-sized Chungkingosaurus. 

Huayangosaurus

Type Species: Huayangosaurus taibaii

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria - Huayangosauridae

Time Period: Middle Jurassic

Location: China 

Diet: Herbivore 

In 1979 the fossilized remains of twelve stegosaurs were discovered in China. These belonged to a new species that lived during the Bathonian and Callovian stages of the Middle Jurassic. Huayangosaurus looked a lot like its later cousin, Stegosaurus, though it was much smaller at only fifteen feet in length. Huayangosaurus lived twenty million years before Stegosaurus and is one of the earliest known stegosaurs (though Europe’s Lexovisaurus beats it to the punch by a few million years). Huayangosaurus’ primitive placement in the stegosaur ‘family tree’ is evidenced by several factors. First, this stegosaur had a broader skull than later stegosaurs, and its skull had a small opening in front of each eye and another small opening in each half of the lower jaw (these openings are absent in later stegosaurs); second, Huayangosaurus had fourteen teeth at the front of its snout (seven on each side), and later stegosaurs lacked these teeth; third, Huayangosaurus had long front limbs that were three-quarters longer than the back limbs, whereas later stegosaurs had forelimbs that were much shorter than the hind limbs; and fifth, the armor plates that ran in two rows along Huayangosaurus’ back were narrower and thicker than those adorning the backs of its later relatives.

a pair of Huayangosaurus with a herd of Omeisaurus

Huayangosaurus nevertheless resembles a ‘proper’ stegosaur. It had the distinctive double row of plates that characterize all stegosaurs; these plates began at its neck and ran along its back until it reached the hips, at which point the plates were replaced with four spikes. After this series of spikes, the plates resumed until they ended with two pairs of long spikes extending horizontally near the end of the tail. These spikes were undoubtedly defensive weapons against such predators as Gasosaurus and Monolophosaurus. Huayangosaurus, like the earlier Lexovisaurus, had two spikes that protruded either from the hips or the shoulders. The exact placement is unknown, with artistic depictions representing either location depending on artistic fancy. The current general consensus is that, as in Lexivosaurus, they were placed on the shoulders; in this case, they would serve as defensive weapons: if an assailant attacked from the front or from the forward side quadrants, Huayangosaurus could ‘thrust’ its spikes deep into the adversary’s hide. In a world without medicine, such penetrating attacks into an enemy’s organs could often be lethal. Only the most foolish of predators would attempt to make a meal out of the armed stegosaur. 

Isaberrysaura

Type Species: Isaberrysaura mollensis

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria 

Time Period: Middle Jurassic

Location: South America (Argentina) 

Diet: Herbivore 

Isaberrysaura was an early stegosaur of South America that had yet to be regulated to fully quadrupedal locomotion. It grew to sixteen to twenty feet in length, making it slightly longer than its Laurasian contemporary Lexovisaurus. Its teeth were heterodont (of different types), and similarities in dentition with modern iguanas indicates that Isaberrysaura may have been omnivorous. We know for certain that it ate plants, because the type specimen was discovered with its stomach contents fossilized for science’s delight. Within the rib cage, a mass of fossilized seeds was discovered, the first preserved meal uncovered in a basal ornithischian. Two types of seeds were present: the largest were preserved in three layers (an outer fleshy sarcotesta, the sclerotesta, and an inner layer that may have been the nucellus); these larger seeds belonged to a cycad of the Zamiineae family. The origin of the smaller seeds are unknown. Because the cycad seeds were swallowed whole, rather than chewed, we can infer that they were in the first stages of digestion in Isaberrysaura’s gut. Scientists speculate that its gut contained enzyme-producing bacteria that aided in the digestion of the tougher seed material. 

Lexivosaurus

Type Species: Lexivosaurus durobrivensis

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria

Time Period: Middle Jurassic

Location: Europe (England, France)

Diet: Herbivore

Lexivosaurus is the first of the ‘standard-looking’ stegosaurs that would rise to prominence in the Late Jurassic. It’s been found in England and France, though it’s more common in England. The first discoveries were made near Lyons, France, and the fossil remains belonged to three individuals and included isolated bits of bones, plates, and spikes. The three individuals were a range of ages, from juvenile to adult, indicating a family group. Lexivosaurus’ name comes from the Lexovix people, one of the ancient Gallic tribal groups from what is now Lyons, France. 

Lexivosaurus was smaller than later stegosaurs, but it was ‘small’ only in comparison: it reached sixteen and a half feet long and weighed around two tons. It was a low-browsing herbivore that roamed the wooded islands that were scattered throughout the shallow seas of prehistoric Europe. Lexivosaurus has back plates that run from its neck to its tail; these plates are narrow and short rather than broad and angular, and it had several pairs of long spikes on the tail. These were likely defensive weapons used against attacking predators such as Magnosaurus, Poekipleuron, and Megalosaurus. Another defensive weapon was the meter-long shoulder spikes that projected from the upper rear part of the front limbs, below the characteristic twin rows of bony plates along the top of its neck and back. While older reconstructions of Lexivosaurus place the spines on the hips, modern paleontologists tend to put them on the shoulders. These spikes may have been used as visual displays – for courtship, fighting rival mates, or species identification – or they may have been defensive weapons, like the tail spikes. If a predator were attacking from the front, Lexivosaurus could thrust itself forward, driving the spikes into the flesh of its assailant. 

Stegosaurus

Type Species: Stegosaurus armatus
Classification: Dinosauria-Ornithischia-Thyreophora-Stegosauria-Stegosauridae-Stegosaurinae
Time Period: late Jurassic
Location: North America & Europe
Diet: Herbivore

The "roofed lizard" is one of the most famous dinosaurs, ranking in popular lore alongside Tyrannosaurus and Triceratops (though Stegosaurus would've never met any of the other two; they were separated by millions of years). Stegosaurus weighed more than two tons and foraged on low-lying plants. Because its diet would've been composed of ground-hugging foilage, it wouldn't had to compete against the titanic sauropods that shared the land during the late Jurassic. Stegosaurus had a small head with weak jaws, and a beak at the front of the mouth chopped vegetation. Inside the mouth, dozens of leaf-shaped teeth ground the vegetation prior to digestation. The front legs were only half as long as its hind legs, but they were stout and able to carry the weight of the dinosaur's "upper-body"; the disproportion between the front and hind legs gave Stegosaurus a steep arch down towards the head, making the hips the tallest part of its body. 

While Tyrannosaurus is known for its scrawny arms and killer teeth, and while Triceratops is known for its three horns and bony frill, Stegosaurus has gathered renown because of the two rows of staggered bony plates running along its back. These plates started off smaller at the head, were biggest at the hips, and then decreased towards the tail. These plates measured several inches thick at the base but became thin and narrow at the tips. These knobs and plates in the skin helped to strengthen and protect the dinosaur's flanks and hips. Some reconstructions even show the plates pointing downward from the back, covering its sides as a sort of roofed protection; these artists speculate that the plates were misaligned at burial. Four ghastly spikes protruded from its tail, and it probably used these as deterrents against the larger predators of the late Jurassic (such as Allosaurus and Ceratosaurus; remember, T-Rex wasn't around!). Here's a famous painting of a Stegosaurus fleeing from a pursuing Allosaurus:

you know he's gonna get it

Endocasts of Stegosaurus' skull show that it had a small brain. This doesn't rule out intelligence, but it certainly doesn't argue for it. In the past, scientists believed that because Stegosaurus had such a tiny brain (about the size of a dog), it must've been a dumb, lumbering animal; this, in turn, led to the widespread belief that all dinosaurs were dumb brutes. Nowadays such a belief is a paleontological anathema (though we can probably assume that Stegosaurus' intelligence is just what would've been needed for a slow-moving, ground-hugging, armored eater). In the burgeoning days of dinosaur discoveries, paleontologists sought to compensate for its small brain by postulating a second brain in its hip region; they based this off the evidence left behind by the sacral plexus, which was a bundle of fleshy nerves that helped with the function of the spinal cord. Regardless of its intelligence, it's still a wicked cool dinosaur, and it could fuck you up. 

you could downright impale yourself on those spikes