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Stegosaurus
Dinosaurthing2
Information
Range North America (USA)
Estimated Population 0
Scientific Classification
Kingdom Animalia
Class Reptile
Order Dinosaur
Family Stegosaurians
Genus Stegosaurus
Conservation Status
EXSpecies
Extinct
Stegosaurus (/ˌstɛɡəˈsɔːrəs/) is a type of armored dinosaur. Their fossilbones have been found in rocks dated to the Late Jurassic period(Kimmeridgian to early Tithonian ages), between 155 and 150 million years ago, in the western United States and Portugal. Several species have been classified in the upper Morrison Formation of the western U.S, though only three are universally recognized; S. stenopsS. ungulatus and S. sulcatus. The remains of over 80 individual animals of this genus have been found. Stegosaurus would have lived alongside dinosaurs such as ApatosaurusDiplodocusBrachiosaurus and Allosaurus and Ceratosaurus; the latter two may have been predators of it.

These were a large, heavily built, herbivorous quadrupeds with rounded backs, short fore limbs, long hind limbs, and tails held high in the air. Due to their distinctive combination of broad, upright plates and tail tipped with spikes, Stegosaurus is one of the most recognizable kinds of dinosaur. The function of this array of plates and spikes has been the subject of much speculation among scientists. Today, it is generally agreed that their spikes were most likely used for defense against predators, while their plates may have been used primarily for display, and secondarily for thermoregulatoryfunctions. Stegosaurus had a relatively low brain-to-body mass ratio. They had short necks and small heads, meaning they most likely ate low-lying bushes and shrubs. One species, Stegosaurus ungulatus, is the largest known of all the stegosaurians (bigger than related dinosaurs such as Kentrosaurus and Huayangosaurus).

Stegosaurus remains were first identified during the "Bone Wars" by Othniel Charles Marsh. The first known skeletons were fragmentary and the bones were scattered, and it would be many years before the true appearance of these animals, including their posture and plate arrangement, became well understood. The name Stegosaurus means "roof lizard" or "covered lizard", in reference to its bony plates. Despite its popularity in books and film, mounted skeletons of Stegosaurus did not become a staple of major natural history museums until the mid-20th century, and many museums have had to assemble composite displays from several different specimens due to a lack of complete skeletons.

Description

The quadrupedal Stegosaurus is one of the most easily identifiable dinosaur genera, due to the distinctive double row of kite-shaped plates rising vertically along the rounded back and the two pairs of long spikes extending horizontally near the end of the tail. Although large individuals could grow up to 9 m (29.5 ft) in length & possibly weighing up to 5,000 kg (5.5 t) making stegosaurus the largest stegosaurian, the various species of Stegosaurs were dwarfed by their contemporaries, the giant sauropods. Stegosaurs had some form of armor which appears to have been necessary, as Stegosaur species coexisted with large predatory theropod dinosaurs, such as Allosaurus and Ceratosaurus.

Most of the information known about Stegosaurus comes from the remains of mature animals; more recently, though, juvenile remains of Stegosaurus have been found. One subadult specimen, discovered in 1994 in Wyoming, is 4.6 m (15.1 ft) long and 2 m (6.6 ft) high, and is estimated to have weighed 2.4 metric tons (2.6 short tons) while alive. It is on display in the University of Wyoming Geological Museum.

Skull

The long and narrow skull was small in proportion to the body. It had a small antorbital fenestra, the hole between the nose and eye common to most archosaurs, including modern birds, though lost in extant crocodylians. The skull's low position suggests that Stegosaurus may have been a browser of low-growing vegetation. This interpretation is supported by the absence of front teeth and their likely replacement by a horny beak or rhamphotheca. The lower jaw of Stegosaurus had a flat upward extension that would have completely hidden the teeth when viewed from the side, and which probably supported a turtle-like beak in life. Other researchers have interpreted these ridges as modified versions of similar structures in other ornithischians which might have supported fleshy cheeks, rather than beaks. Stegosaurian teeth were small, triangular, and flat; wear facets show that they did grind their food. The jaws of Stegosaurus had flat downward and upward extensions that would have completely hidden the teeth when viewed from the side, and these probably supported a beak in life. The presence of a beak extended along much of the jaws may have precluded the presence of cheeks in these species. Such an extensive beak was probably unique to Stegosaurus and some other advanced stegosaurids among ornithischians, which usually had beaks restricted to the jaw tips.

Despite the animal's overall size, the braincase of Stegosaurus was small, being no larger than that of a dog. A well-preserved Stegosaurus braincase allowed Othniel Charles Marsh to obtain, in the 1880s, a cast of the brain cavity or endocast of the animal, which gave an indication of the brain size. The endocast showed the brain was indeed very small, the smallest proportionally of all dinosaur endocasts then known. The fact that an animal weighing over 4.5 metric tons(5 short tons) could have a brain of no more than 80 g (2.8 oz) contributed to the popular old idea that all dinosaurs were unintelligent, an idea now largely rejected. Actual brain anatomy in Stegosaurus is poorly known, but the brain itself was, however, small even for a dinosaur, fitting well with a slow, herbivorous lifestyle and limited behavioural complexity.

Skeleton

In Stegosaurus stenops there are 27 bones in the vertebral column anterior to the sacrum, a varying number of vertebrae in the sacrum, with four in most subadults, and around 46 caudal (tail) vertebrae. The presacrals are divided into cervical (neck) and dorsal (back) vertebrae, with around 10 cervicals and 17 dorsals, the total number being one greater than in Hesperosaurus, two greater than Huayangosaurus, although Miragaia preserves 17 cervicals and an unknown number of dorsals. The first cervical vertebra is the axis bone, which is connected and often fused to the atlas bone. Farther posteriorly, the proportionately larger the cervicals become, although they do not change greatly in anything other than size. Past the first few dorsals, the centrum of the bones become more elongate front-to-back, and the transverse processes become more elevated dorsal. The sacrum of S. stenopsincludes four sacral vertebrae, but one of the dorsals is also incorporated into the structure. In some specimens of S. stenops, a caudal is also incorporated, as a caudosacral. In Hesperosaurus there are two dorsosacrals, and only four fused sacrals, but in Kentrosaurus there may be as many as seven vertebrae in the sacrum, with both dorsosacrals and caudosacrals. S. stenops preserves 46 caudal vertebrae, and up to 49, and along the series both the centrums and the neural spines become smaller, until the neural spines disappear at caudal 35. Around the middle of the tail, the neural spines become bifurcated, meaning they are divided near the top.

With multiple well-preserved skeletons, S. stenops preserves all regions of the body, including the limbs. The scapula (shoulder blade) is sub-rectangular, with a robust blade. Though it is not always perfectly preserved, the acromion ridge is slightly larger than in Kentrosaurus. The blade is relatively straight, although it curves towards the back. There is a small bump on the back of the blade, that would have served as the base of the tricepsmuscle. Articulated with the scapula, the coracoid is sub-circular. The hind feet each had three short toes, while each fore foot had five toes; only the inner two toes had a blunt hoof. The phalangeal formula is 2-2-2-2-1, meaning the innermost finger of the fore limb has two bones, the next has two, etc. All four limbs were supported by pads behind the toes. The fore limbs were much shorter than the stocky hind limbs, which resulted in an unusual posture. The tail appears to have been held well clear of the ground, while the head of Stegosaurus was positioned relatively low down, probably no higher than 1 m (3.3 ft) above the ground.

Plates

The most recognizable features of Stegosaurus are its dermal plates, which consisted of between 17 and 22 separate plates and flat spines. These were highly modified osteoderms (bony-cored scales), similar to those seen in crocodiles and many lizards today. They were not directly attached to the animal's skeleton, instead arising from the skin. The largest plates were found over the hips and could measure up to 60 cm (2.0 ft) wide and 60 cm tall.

In a 2010 review of Stegosaurus species, Peter Galton suggested that the arrangement of the plates on the back may have varied between species, and that the pattern of plates as viewed in profile may have been important for species recognition. Galton noted that the plated in S. stenops have been found articulated in two staggered rows, rather than paired. Fewer S. ungulatus plates have been found, and none articulated, making the arrangement in this species more difficult to determine. However, the type specimen of S. ungulatus preserves two flattened spine-like plates from the tail that are nearly identical in shape and size, but are mirror images of each other, suggesting that at least these were arranged in pairs.

Palaeobiology

Locomotion

Professor Marsh who discovered the species with the first specimen considered stegosaurs to be bipedal, due to its short front limbs. But later he realised by 1891 that it was quadrupedal after considering the animals heavy build body, stegosaurus had rather short fore limbs in relation to its hind limbs. Furthermore The within the hind limbs, the lower section (comprisin the tibia & fibula) was short compared with the femur. This suggests that a stegosaurus could not have walked very fast, as the stride of the back legs at speed would have overtaken the front legs, so the maximum speed of a stegosaurus was 6-7 km/h (3.7-4.3 mph). Although stegosaurus is quadrupedal, some discussion has occurred over whether it could rear up on its hind legs to browse on higher foliage. This was proposed by Bakker & opposed by Carpenter.

Behaviour

Stegosaurs may have been social creatures, living in multiple-age group Herds, track ways discoverd by Matthew Mossbrucker (from the Morrison natural history museum in Colorado) suggests they did. One group of tracks is interpreted showing four or five baby stegosaurs moving in the same direction, while other tracks from a juvenile stegosaur with other tracks from an adult overpreted them.

Diet

Stegosaurus and related genera were herbivores. However, their teeth and jaws are very different from those of other herbivorous ornithischian dinosaurs, suggesting a different feeding strategy that is not yet well understood. The other ornithischians possessed teeth capable of grinding plant material and a jaw structure capable of movements in planes other than simply orthal (i.e. not only the fused up-down motion to which stegosaur jaws were likely limited). Unlike the sturdy jaws and grinding teeth common to its fellow ornithischians, Stegosaurus (and all stegosaurians) had small, peg-shaped teeth that have been observed with horizontal wear facets associated with tooth-food contact and their unusual jaws were probably capable of only orthal (up-down) movements. Their teeth were "not tightly pressed together in a block for efficient grinding", and no evidence in the fossil record of stegosaurians indicates use of gastroliths—the stone(s) some dinosaurs (and some present-day bird species) ingested—to aid the grinding process, so how exactly Stegosaurus obtained and processed the amount of plant material required to sustain its size remains "poorly understood".

The stegosaurians were widely distributed geographically in the late Jurassic. Palaeontologists believe it would have eaten plants such as mosses, ferns, horsetails, cycads, and conifers or fruits. Grazing on grasses, seen in many modern mammalian herbivores, would not have been possible for Stegosaurus, as grasses did not evolve until late into the Cretaceous Period, long after Stegosaurus had become extinct.

One hypothesized feeding behavior strategy considers them to be low-level browsers, eating low-growing fruit of various nonflowering plants, as well as foliage. This scenario has Stegosaurus foraging at most 1 m above the ground. Conversely, if Stegosaurus could have raised itself on two legs, as suggested by Bakker, then it could have browsed on vegetation and fruits quite high up, with adults being able to forage up to 6 m (20 ft) above the ground.

A detailed computer analysis of the biomechanics of Stegosaurus's feeding behavior was performed in 2010, using two different three-dimensional models of Stegosaurus teeth given realistic physics and properties. Bite force was also calculated using these models and the known skull proportions of the animal, as well as simulated tree branches of different size and hardness. The resultant bite forces calculated for Stegosaurus were 140.1 Newton (N), 183.7 N, and 275 N (for anterior, middle and posterior teeth, respectively), which means its bite force was less than half that of a Labrador Retriever. Stegosaurus could have easily bitten through smaller green branches, but would have had difficulty with anything over 12 mm in diameter. Stegosaurus, therefore, probably browsed primarily among smaller twigs and foliage, and would have been unable to handle larger plant parts unless the animal was capable of biting much more efficiently than predicted in this study.

Tail spikes

The tail spikes (or thagomizers) are a stegosaurs only defence against predators, although the plates that run down its tail would be of a hindrance to its flexibility, stegosaurus would likely have been able to pivot its hind legs easily keeping its tail presented to swing at a predator attacking it like a allosaurus. In fact remains of an allosaur has been found that shows a serious injury to its tail vertebrae, from examination it was made by tail spikes of a stegosaurus. Early representations had the spikes arranged upwards on the tails of stegosaurs, but further studies have shown that a stegosaurs thagomizers stuck out sideways on its tail.

Plate functions

The functions of plates of stegosaurs has been demanding of understanding, it was once thought that they were for defence but the plates were actually very fragile & would not been able to withstand such punishment from being bitten by predators, so there weren't for defence so there two most likely theories for the functions of the plates. One theory is that stegosaurs use there plates for thermoregulation, & the evidence for this comes from grooves in the plates that would have allowed blood vessels to run through them. The blood would then be carried close to the skin where temperature adjustment could take place, so a stegosaurus could warm its self up & cool its self down. The second theory which most paleozoologists can agree with, is that stegosaurs use there plates for display, particularly males would use there plates to intimidating rival males & attracting females, this may have involved the flushing of blood into the plates to provide a vivid colour display necessitating the for blood vessels in the plates. But one argument against both the thermoregulation & colour change is that the plates were covered in keratin (same stuff that rhino horn is made of), which would have not allowed rapid visual colour change or efficient heat exchange.

Juveniles

Juveniles of stegosaurs have been preserved, probably showing the growth of the genus. Kentrosaurus (a relative of stegosaurus) is also known from juvenile specimens, and they can be identified as different genders. The two juveniles are both relatively small, with the smaller individual being 1.5 m (4.9 ft) long, and the larger one having a length of 2.6 m (8.5 ft). The specimens can be identified as not mature because they lack the fusion of the scapula & coracoid, and the lower hind limbs. Also, the pelvic region of the specimens are similar to those of juvenile kentrosaurs.

Discovery and history

Stegosaurus, one of the many dinosaurs first collected and described in the Bone Wars, was originally named by Othniel Charles Marsh in 1877, from remains recovered north of Morrison, Colorado. These first bones became the holotype of Stegosaurus armatus. Marsh initially believed the remains were from an aquatic turtle-like animal, and the basis for its scientific name, 'roof(ed) lizard' was due to his early belief that the plates lay flat over the animal's back, overlapping like the shingles (tiles) on a roof. A wealth of Stegosaurus material was recovered over the next few years, and Marsh published several papers on the genus from 1877 to 1897. In 1878, Edward Drinker Cope named Hypsirhophus discurus, as another stegosaurian based on fragmentary fossils specimens from Cope’s Quarry 3 near the "Cope's Nipple" site in Garden Park, Colorado. Many later researchers have considered Hypsirhophus to be a synonym of Stegosaurus, though Peter Galton (2010) suggested that it is distinct based on differences in the vertebrae.

Marsh named a second species, Stegosaurus ungulatus, in 1879, and finally gave a more detailed description of all the Stegosaurus fossils collected to far the following year. In 1881, he named a third species Stegosaurus "affinis", based only on a hip bone. This species is generally agreed to have been inadequately described, and therefore is a nomen nudum (a name lacking a formal description). The specimen was later lost. Marsh continued to collect and examine new Stegosaurus specimens, and in 1887 he named three new species: Stegosaurus stenopsS. duplex, and S. sulcatus. Though it had not yet been completely prepared, the nearly complete and articulated type specimen of Stegosaurus stenops allowed Marsh to complete the first attempt at a reconstructed Stegosaurus skeleton. This first reconstruction, of S. ungulatus with missing parts filled in from S. stenops, was published by Marsh in 1891. (In 1893, Richard Lydekker mistakenly re-published Marsh's drawing under the label Hypsirhophus).

The next species of Stegosaurus to be named was S. marshi, by Frederick Lucas in 1901. Lucas reclassified this species in the new genus Hoplitosaurus later that year. Lucas also re-examined the issue of the life appearance of Stegosaurus, coming to the conclusion that the plates were arranged in pairs in two rows along the back, arranged above the bases of the ribs. Lucas commissioned Charles R. Knight to produce a life restoration of S. ungulatus based on his new interpretation. However, the following year, Lucas wrote that he now believed the plates were probably attached in staggered rows. In 1910, Richard Swann Lull wrote that the alternating pattern seen in S. stenops was probably due to shifting of the skeleton after death. He led the construction of the first ever Stegosaurusskeletal mount at the Peabody Museum of Natural History, which was depicted with paired plates. In 1914, Charles Gilmore argued against Lull's interpretation, noting that several specimens of S. stenops, including the now-completely prepared holotype, preserved the plates in alternating rows near the peak of the back, and that there was no evidence of the plates having shifted relative to the body during fossilization. Gilmore and Lucas' interpretation became the generally accepted standard, and Lull's mount at the Peabody Museum was changed to reflect this in 1924.

Plate arrangement

One of the major subjects of books and articles about Stegosaurus is the plate arrangement. The argument has been a major one in the history of dinosaur reconstruction. Four possible plate arrangements have been proposed over the years:

  • The plates lie flat along the back, as a shingle-like armor. This was Marsh's initial interpretation, which led to the name 'roof lizard'. As further and complete plates were found, their form showed they stood on edge, rather than lying flat.
  • By 1891, Marsh published a more familiar view of Stegosaurus, with a single row of plates. This was dropped fairly early on (apparently because it was poorly understood how the plates were embedded in the skin and they were thought to overlap too much in this arrangement). It was revived, in somewhat modified form, in the 1980s, by Stephen Czerkas, based on the arrangement of iguana dorsal spines.
  • The plates were paired in a double row along the back. This is probably the most common arrangement in illustrations, especially earlier ones. The Stegosaurus in the 1933 film, King Kong, has this arrangement.
  • Two rows of alternating plates. By the early 1960s, this had become (and remains) the prevalent idea, mainly because some S. stenops fossils in which the plates are still partially articulated show this arrangement.

Classification and Evolution

Stegosaurus was the first-named genus of the family Stegosauridae. It is the type genus that gives its name to the family. The Stegosauridae are one of two families within the infraorder Stegosauria, with the other being the Huayangosauridae. The infraorder Stegosauria lies within the Thyreophora, or armored dinosaurs, a suborder which also includes the more diverse ankylosaurs. The stegosaurs were a clade of animals similar in appearance, posture, and shape that mainly differed in their array of spikes and plates. Among the closest relatives to Stegosaurus are Wuerhosaurus from China and Kentrosaurus from East Africa.

The following cladogram shows the position of Stegosaurus within the Stegosauridae according to Mateus, 2009:

{|

|Stegosauridae | rowspan="2" |


Kentrosaurus



Loricatosaurus




Dacentrurus


Miragaia




Stegosaurus



Wuerhosaurus


Hesperosaurus





|- |
|}


Evolutionary Origin

The origin of Stegosaurus is uncertain, as few remains of basal stegosaurs and their ancestors are known. Recently, stegosaurids have been shown to be present in the lower Morrison Formation, existing several million years before the occurrence of Stegosaurus itself, with the discovery of the related Hesperosaurus from the early Kimmeridgian. The earliest stegosaurid (the genus Lexovisaurus) is known from the Oxford Clay Formation of England and France, giving it an age of early to middle Callovian.

The earlier and more basal genus Huayangosaurus from the Middle Jurassic of China (some 165 million years ago – Mya) antedates Stegosaurus by 20 million years and is the only genus in the family Huayangosauridae. Earlier still is Scelidosaurus, from Early Jurassic England, which lived about 190 Mya. Interestingly, it possessed features of both stegosaurs and ankylosaurs. Emausaurus from Germany was another small quadruped, while Scutellosaurus from Arizonawas an even earlier genus and was facultatively bipedal. These small, lightly armored dinosaurs were closely related to the direct ancestor of both stegosaurs and ankylosaurs. A trackway of a possible early armored dinosaur, from around 195 Mya, has been found in France.

Species

Initially, several species were described. However, many of these have since been considered to be invalid or synonymous with existing species, leaving two well-known and one poorly known species. Confirmed Stegosaurus remains have been found in the Morrison Formation's stratigraphic zones 2–6, with additional remains possibly referrable to Stegosaurusrecovered from stratigraphic zone 1.

  • Stegosaurus ungulatus, meaning "hoofed roof lizard", was named by Marsh in 1879, from remains recovered at Como Bluff, Wyoming (Quarry 12, near Robber's Roost). It might be synonymous with S. stenops. At 9 m (29.5 ft), it was the longest species within the genus Stegosaurus. A fragmentary Stegosaurus specimen discovered in Portugal and dating from the upper Kimmeridgian-lower Tithonian stage has been tentatively assigned to this species. Stegosaurus ungulatus can be distinguished from S. stenops by the presence of smaller, more triangular plates and by several pairs of small, flat, pointed plates just before the spikes on the tail. These spine-like plates appear to have been paired, due to the presence of at least one pair that are identical but mirrored. S. ungulatus also appears to have had longer legs (femora) and hip bones than other species. The type specimen of S. ungulatus was discovered with eight spikes, though they were scattered away from their original positions. These have often been interpreted as indicating that the animal had four pairs of tail spikes. No specimens have been found with complete or articulated sets of tail spikes, but no additional specimens have been found that preserve eight spikes together. It is possible the extra pair of spikes came from a different individual, and though no other extra bones were found with the specimen, these may be found if more digging were done at the original site. Specimens from other quarries (such as a tail from Quarry 13, now forming part of the composite skeleton AMNH 650 at the American Museum of Natural History), referred to S. ungulatus on the basis of their notched tail vertebrae, are preserved with only four tail spikes. The type specimen of S. ungulatus (YPM 1853) was incorporated into the first ever mounted skeleton of a stegosaur at the Peabody Museum of Natural History in 1910 by Richard Swann Lull. It was initially mounted with paired plates set wide, above the base of the ribs, but was remounted in 1924 with two staggered rows of plates along the midline of the back. Additional specimens recovered from the same quarry by the United States National Museum of Natural History, including tail vertebrae and an additional large plate (USNM 7414), belong to the same individual as YPM 1853.
  • Stegosaurus stenops, meaning "narrow-faced roof lizard", was named by Marsh in 1887, with the holotype having been collected by Marshal Felch at Garden Park, north of Cañon City, Colorado, in 1886. This is the best-known species of Stegosaurus, mainly because its remains include at least one complete articulated skeleton. It had proportionately large, broad plates and rounded tail plates. Articulated specimens show that the plates were arranged alternating in a staggered double row. S. stenops is known from at least 50 partial skeletons of adults and juveniles, one complete skull, and four partial skulls. It was shorter than other species, at 7 m (23 ft). Found in the Morrison Formation, Colorado, Wyoming, and Utah.
  • Stegosaurus sulcatus, meaning "furrowed roof lizard", was described by Marsh in 1887 based on a partial skeleton. It has traditionally been considered a synonym of S. armatus, though more recent studies suggest it is not. S. sulcatus is distinguished mainly by its unusually large, furrowed spikes with very large bases. A spike associated with the type specimen, originally thought to be a tail spike, may in fact come from the shoulder or hip, since its base is much larger than the corresponding tail vertebrae. A review published by Maidment and colleagues in 2008 regarded it as an indeterminate species possibly not even belonging to Stegosaurus at all, but to a different genus. Peter Galton suggested it should be considered a valid species due to its unique spikes.

Susannah Maidment and colleagues in 2008 proposed extensive alterations to the taxonomy of Stegosaurus. They advocated synonymizing S. stenops and S. ungulatus with S. armatus, and sinking Hesperosaurus and Wuerhosaurus into Stegosaurus, with their type species becoming Stegosaurus mjosi and Stegosaurus homheni, respectively. They regarded S. longispinus as dubious. Thus, their conception of Stegosaurus would include three valid species (S. armatusS. homheni, and S. mjosi) and would range from the Late Jurassic of North America and Europe to the Early Cretaceous of Asia. However, this classification scheme has not generally been followed by other researchers. Galton, for example, has stated that Wuerhosaurus differs enough from Stegosaurus to be retained as a distinct genus. In 2015, Maidment et al. revised their suggestion due to the recognition by Galton of S. armatus as a nomen dubium and its replacement by S. stenops as type species.

Doubtful species and junior synonyms

  • Stegosaurus armatus, meaning "armored roof lizard", was the first species to be found and the original type species named by O.C. Marsh in 1877. It is known from a partial skeletons, and more than 30 fragmentary specimens have been referred to it. However, the type specimen was very fragmentary, consisting only of a partial tail, hips, and leg, parts of some back vertebrae, and a single fragmentary plate (the presence of which was used to give the animal its name). No other plates or spikes were found, and the entire front half of the animal appears not to have been preserved. Because the type specimen is very fragmentary, it is extremely difficult to compare it with other species based on better specimens, and it is now generally considered to be a nomen dubium. Because of this, it was replaced by S. stenops as the type species of Stegosaurus in a ruling of the ICZN in 2013.
  • Stegosaurus "affinis", named by Marsh in 1881, is only known from a pubis which has since been lost. Because Marsh did not provide an adequate description of the bone with which to distinguish a new species, this name is considered a nomen nudum.
  • Diracodon laticeps was described by Marsh in 1881, from some jawbone fragments. Bakker resurrected D. laticeps in 1986 as a senior synonym of S. stenops, although others note that the material is not diagnostic and is only referable to Stegosaurus sp., making it a nomen dubium.
  • Stegosaurus duplex, meaning "two plexus roof lizard" (in allusion to the greatly enlarged neural canal of the sacrum which Marsh characterized as a "posterior brain case"), was named by Marsh in 1887 (including the holotype specimen). The disarticulated bones were actually collected in 1879 by Edward Ashley at Como Bluff. Marsh initially distinguished it from S. ungulatus based on the fact that each sacral (hip) vertebra bore its own rib, which he claimed was unlike the anatomy of S. ungulatus; however, the sacrum of S. ungulatus had not actually been discovered. Marsh also suggested that S. duplex may have lacked armor, since no plates or spikes were found with the specimen, though a single spike may actually have been present nearby, and re-examination of the site maps has shown that the entire specimen was found highly disarticulated and scattered. It is generally considered a synonym of S. ungulatus today, and parts of the specimen were actually incorporated into the Peabody Museum S. ungulatus skeletal mount in 1910.

Reassigned species

  • Stegosaurus marshi, which was described by Lucas in 1901, was renamed Hoplitosaurus in 1902.
  • Stegosaurus priscus, described by Nopcsa in 1911, was reassigned to Lexovisaurus, and is now the type species of Loricatosaurus.
  • Stegosaurus longispinus was named by Charles W. Gilmore. It is now the type species of the genus Alcovasaurus.
  • Stegosaurus madagascariensis from Madagascar is known solely from teeth and was described by Piveteau in 1926. The teeth were variously attributed to a stegosaur, the theropod Majungasaurus, a hadrosaur or even a crocodylian, but is now considered a possible ankylosaur.

Paleoecology

Stegosaurs may have preferred living in drier settings then other common dinosaurs that lived in the Morrison formation like allosaurs, apatosaurs & camarasaurs. The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains. Vegetation varied from river-lining forests of conifers, tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, ferns, cycads, ginkoes, and several families of conifers. Animal fossils discovered include bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans, several species of pterosaurs, numerous dinosaur species, and early mammals such as docodonts, multituberculates, symmetrodonts, and triconodonts.

Dinosaurs that lived alongside Stegosaurus included theropods AllosaurusSaurophaganaxTorvosaurusCeratosaurusMarshosaurusStokesosaurusOrnitholestesCoelurus and Tanycolagreus. Sauropods dominated the region, and included BrachiosaurusApatosaurusDiplodocusCamarasaurus, and Barosaurus. Other ornithischians included CamptosaurusGargoyleosaurusDryosaurusOthnielosaurus and Drinker. Stegosaurus is commonly found at the same sites as AllosaurusApatosaurusCamarasaurus, and Diplodocus.

Extinction

In popular culture

One of the most recognizable of all dinosaurs, Stegosaurus has been depicted on film, in cartoons and comics, as children's toys, and was even declared the State Dinosaur of Colorado in 1982. Due to the fragmentary nature of most early Stegosaurus fossil finds, it took many years before reasonably accurate restorations of these animals could be produced. The earliest popular image of Stegosaurus was an engraving produced by A. Tobin for the November 1884 issue of Scientific American, which included the dinosaur amid a speculative Morrison age landscape. Tobin restored the Stegosaurus as bipedal and long-necked, with the plates arranged along the tail and the back covered in spikes. This covering of spikes might have been based on a misinterpretation of the teeth, which Marsh had noted were oddly shaped, cylindrical, and found scattered, such that he thought they might turn out to be small dermal spines.

Marsh published his more accurate skeletal reconstruction of Stegosaurus in 1891, and within a decade Stegosaurus had become among the most-illustrated types of dinosaur. Artist Charles R. Knight published his first illustration of Stegosaurus ungulatus based on Marsh's skeletal reconstruction in a November 1897 issue of Century Magazine. This illustration would later go on to form the basis of the stop-motion puppet used in the 1933 film King Kong. Like Marsh's reconstruction, Knight's first restoration had a single row of large plates, though he next used a double row for his more well-known 1901 painting, produced under the direction of Frederic Lucas. Again under Lucas, Knight revised his version of Stegosaurus again two years later, producing a model with a staggered double row of plates. Knight would go on to paint a stegosaur with a staggered double plate row in 1927 for the Field Museum of Natural History, and was followed by Rudolph F. Zallinger, who painted Stegosaurus this way in his "Age of Reptiles" mural at the Peabody Museum in 1947.

Stegosaurus made its major public debut as a papier mache model commissioned by the U.S. National Museum of Natural History for the 1904 Louisiana Purchase Exposition. The model was based on Knight's latest miniature with the double row of staggered plates, and was exhibited in the United States Government Building at the exposition in St. Louisbefore being relocated to Portland, Oregon for the Lewis and Clark Centennial Expositionin 1905. The model was moved to the Smithsonian National Museum of Natural History (now the Arts and Industries Building) in Washington, D.C. along with other prehistory displays, and to the current National Museum of Natural History building in 1911. Following renovations to the museum in the 2010s, the model was moved once again for display at the Museum of the Earth in Ithaca, New York.

The popularity of Stegosaurus is owed partly to its prominent display in natural history museums. Though considered one of the most distinctive types of dinosaur, Stegosaurusdisplays were missing from a majority of museums during the first half of the 20th century, due largely to the disarticulated nature of most fossil specimens. Until 1918, the only mounted skeleton of Stegosaurus in the world was O.C. Marsh's type specimen of S. ungulatus at the Peabody Museum of Natural History, which was put on display in 1910. However, this mount was dismantled in 1917 when the old Peabody Museum building was demolished. This historically significant specimen was re-mounted ahead of the opening of the new Peabody Museum building in 1925. 1918 saw the completion of the second Stegosaurus mount, and the first depicting S. stenops. This mount was created under the direction of Charles Gilmore at the U.S. National Museum of Natural History. It was a composite of several skeletons, primarily USNM 6531, with proportions designed to closely follow the S. stenops type specimen, which had been on display in relief nearby since 1918. The aging mount was dismantled in 2003 and replaced with a cast in an updated pose in 2004. A third mounted skeleton of Stegosaurus, referred to S. stenops, was put on display at the American Museum of Natural History in 1932. Mounted under the direction of Charles J. Long, the American Museum mount was a composite consisting of partial remains filled in with replicas based on other specimens. In his article about the new mount for the museum's journal, Barnum Brown described (and disputed) the popular misconception that the Stegosaurus had a "second brain" in its hips. Another composite mount, using specimens referred to S. ungulatus collected from Dinosaur National Monument between 1920 and 1922, was put on display at the Carnegie Museum of Natural History in 1940.

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