Stegosaurus

StegosaurusStegosaurus armatus
Pronounced	Steg - o - Saw - rus
Year Named	1877
Diet	Herbivore (Plant-Eater)
Name Means	"roofed lizard"
Length	32 feet (10 m)
Height	13 feet (4 m)
Weight	2 tons (1,800 kilos)
Time	Late Jurassic - 155 MYA
Location	Western U.S., possibly Madagascar
Taxon	Ornithischia, Thyreophora, Stegosauria

Stegosaurus (pronounced ˌstɛgəˈsɔrəs) is a genus of stegosaurid armoured dinosaur from the Late Jurassic period (late Kimmeridgian to Early Tithonian) in what is now western North America. In 2006, a specimen of Stegosaurus was announced from Portugal, showing that they were present in Europe as well. Due to its distinctive tail spikes and plates, Stegosaurus is one of the most recognizable dinosaurs, along with Tyrannosaurus, Triceratops, and Apatosaurus. The name Stegosaurus means "roof-lizard" and is derived from the Greek στέγος-, stegos- ("roof") and σαῦρος, -sauros ("lizard") At least three species have been identified in the upper Morrison Formation and are known from the remains of about 80 individuals. They lived some 150 to 145 million years ago, in an environment and time dominated by the giant sauropods Diplodocus, Camarasaurus, and Apatosaurus.

A large, heavily built, herbivorous quadruped, Stegosaurus had a distinctive and unusual posture, with a heavily arched back, short forelimbs, head held low to the ground and a stiffened tail held high in the air. Its array of plates and spikes has been the subject of much speculation. The spikes were most likely used for defense, while the plates have also been proposed as a defensive mechanism, as well as having display and thermoregulatory (heat control) functions. Stegosaurus was the largest of all the stegosaurians (bigger than genera such as Kentrosaurus and Huayangosaurus) and, although roughly bus-sized, it nonetheless shared many anatomical features (including the tail spines and plates) with the other stegosaurian genera.

Description

The size of a Stegosaurus compared to a human.

Averaging less than metres (29.5 ft) long and 4 metres (13 ft) tall, the quadrupedal Stegosaurus is one of the most easily identifiable dinosaurs, due to the distinctive double row of kite-shaped plates rising vertically along its arched back and the two pairs of long spikes extending horizontally near the end of its tail. Although a large animal, it was dwarfed by its contemporaries the giant sauropods. Some form of armour appears to have been necessary, as it coexisted with large predatory theropod dinosaurs, such as the fearsome Allosaurus and Ceratosaurus.

The hind feet each had three short toes, while each forefoot had five toes; only the inner two toes had a blunt hoof. All four limbs were supported by pads behind the toes.The forelimbs were much shorter than the stocky hindlimbs, 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 metre (3.3 ft) above the ground.

Life restoration of Stegosaurus sulcatus with alternating plate arrangement.

S. stenops skull cast, Natural History Museum of Utah

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 replacement by a horny beak or rhamphotheca. Stegosaurian teeth were small, triangular and flat wear facets show that they did grind their food. The inset placement in the jaws suggests that Stegosaurus had cheeks to keep food in their mouths while they chewed.

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 that the brain was indeed very small, maybe the smallest among the dinosaurs. The fact that an animal weighing over 4.5 tonnes (5 US short tons) could have a brain of no more than 80 grams (2.8 oz) contributed to the popular old idea that 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.

Life restoration of Sophie, depicting the modern view of S. stenops

Most of the information known about Stegosaurus comes from the remains of mature animals; however more recently juvenile remains of Stegosaurus have been found. One sub-adult specimen, discovered in 1994 in Wyoming, is 4.6 metres (15 ft) long and 2 metres (7 ft) high, and is estimated to have weighed 2.3 tonnes (2.6 short tons) while alive. It is on display in the University of Wyoming Geological Museum. Even smaller skeletons, 210 centimetres (6.9 ft) long and 80 centimetres (2.6 ft) tall at the back, are on display at the Denver Museum of Nature & Science.

S. stenops has 27 bones in the vertebral column anterior to the sacrum, with the sacrum having 4 in most subadults and ~46 caudals. There are ~10 cervicals and ~17 dorsals, having a greater total than Hesperosaurus, 2 greater than Huayangosaurus and probably less than Miragaia. The cervicals become larger posteriorly. The centra become elongate past the first few dorsals, front-to-back, with the transverse processes becoming more dorsally elevated. ne of the dorsals incorporates into the sacrals, with some including a caudosacral. S. stenops has 46 caudals, and up to 49, with the neural spines shrinking along both centra series, where they disappear at caudal 35. The mid-tail has bifurcated neural spines.

Mounted composite skeleton referred to S. ungulatus, Carnegie Museum of Natural History

Multiple well-preserved S. stenops show all regions of the body. The scapula is sub-rectangular with a robust blade. The acromion ridge is slightly larger than Kentrosaurus, though not always fully preserved. The blade is somewhat straight, curving nearer to the posterior. A small bump adorns the back of the blade, which would have anchored the triceps. The coracoid is sub-circular and articulates with the scapula.. The hindlegs have 3 digits and 5 on the forelegs. All limbs were supported by pads behind the toes. The inner two toes on the forefeet bear a blunt hoof. The phalangeal formula is 2-2-2-2-1. The forelimbs were much shorter, which results in a strange posture. The tail is held clear if the ground with the head positioned low down, likely no higher than 1 meter (3.3 feet) high.

It had 17 and 22 separate plates, which were highly-modified osteoderms. They were not directly attached, arising from the skin, The largest plate were over the hips, measuring over 60 centimeters (24 inches) wide and 60 centimeters (24 inches) tall. Galton (2010) suggested these may have varied between species, and that their appearance in profile may have identified species, The type S. ungulatus has flattened spine-like plates in the tail that are near-identical in shape and size, being mirrored, suggesting they were arranged in pairs. Most plates are manifestly chiral, with no two being the same in a single individual, but they have instead been correlated between individuals. Integument in Hesperosaurus plates have a smooth surface with long, parallel, shallow grooves, indicating a keratinous sheath.

Tyler Greenfield proposes "Stegosaurus" sulcatus is a dacentrurine due to similar dermal spines. Thus, the species "sulcatus" would make the Morrison dacentrurine Alcovasaurus/Miragaia sulcatus.

Classification

Restoration of S. ungulatus

Back plate cast, Museum of the Rockies, Bozeman, Montana

Stegosaurus was the first-named genus of the family Stegosauridae. It is the type genus that gives its name to the family. Stegosauridae is one of two families within the infraorder Stegosauria, with the other being Huayangosauridae. Stegosauria lies within the Thyreophora, or armoured 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.

Stegosaurus frequently is discovered in its own clade in Stegosauridae called Stegosauridae, usually including the taxa Wuerhosaurus and Loricatosaurus, though Hesperosaurus is sometimes found in the group. in 2017, Raven and Maidment published a new phylogenetic analysis, including almost every known stegosaurian genus:

Thyreophora

Lesothosaurus diagnosticus Laquintasaura venezuelae Scutellosaurus lawleri Emausaurus ernsti Scelidosaurus harrisonii Alcovasaurus longispinus Eurypoda Ankylosauria Sauropelta edwardsi Gastonia burgei Euoplocephalus tutus Stegosauria Huayangosauridae Huayangosaurus taibaii Chungkingosaurus jiangbeiensis Tuojiangosaurus multispinus Paranthodon africanus Stegosauridae Jiangjunosaurus junggarensis Gigantspinosaurus sichuanensis Kentrosaurus aethiopicus Dacentrurus armatus Loricatosaurus priscus Hesperosaurus mjosi Miragaia longicollum Stegosaurus stenops Wuerhosaurus homheni

Origins

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) predates Stegosaurus by 20 million years and is the only genus in the family Huayangosauridae. Earlier still is Scelidosaurus, from Early Jurassic England, which lived approximately 190 million years ago. Interestingly, it possessed features of both stegosaurs and ankylosaurs. Emausaurus from Germany was another small quadruped, while Scutellosaurus from Arizona in the USA was an even earlier genus and was facultatively bipedal. These small, lightly-armoured dinosaurs were closely related to the direct ancestor of both stegosaurs and ankylosaurs. A trackway of a possible early armoured dinosaur, from around 195 million years ago, has been found in France.

History

The first mounted skeleton of a stegosaur (S. ungulatus), Peabody Museum of Natural History, 1910

1901 life restoration of S. ungulatus by Charles R. Knight with paired dorsal plates and eight tail spikes

Stegosaurus was named by Othniel Charles Marsh (1877) during the bone wars. These first remains were assigned to S. armatus, believing them to be of an aquatic turtle-like animal, naming it the "roofed lizard" due to his interpretation that they lay flat over the back, somewhat like shingles. Much more material was found in the next years, from which Marsh continued to study until 1897. Edward Drinker Cope (1878) named Hypsirhopus discurus, a fragmentary stegosaur from Cope's Nipple site, Cope's Quarry 3, Garden Park, Colorado. Many later assigned these to Stegosaurus, though vertebral differences highlighted by Peter Galton (2010) suggests it may be distinct. S. ungulatus, named by Marsh (1879) gave a detailed description of Stegosaurus collected the following year. S. "affinis" was named by Marsh (1881) from a pelvis, but it is thought to have an insufficient description, so it is a nomen nudum. Later, however, this specimen was lost.

Marsh continued to collect and study new specimens, naming S. stenops, duplex and sulcatus in 1887. Though not fully prepared at the time, the near-articulate S. stenops allowed him to fully reconstruct the entire animal. The first S. ungulatus paleoillustration filled missing elements with S. stenops, and published by him in 1891. However, Richard Lydekker (1893) accidentally published the skeletal under Hypsirhopus.

S. marshi was named by Frederick Lucas (1901), which he later merged with Hoplitosaurus, re-examining the plate formation, which he found to form double rows above each rib base. He commissioned Charles R. Knight to create S. ungulatus paleoart. Later the following year, Lucars re-reexamined the plates, finding they likely sat in staggered rows. Richard Swann Lull (1910) the staggered pattern was due to shifting of the skeleton after death, mounting the first skeletal mount at the Peabody Museum of Natural History, which had paired plates. Charles Gilmore (1914) debated this, noting several S. stenops (now including the fully-prepared holotype) preserved alternating plates near the back's peak, having no evidence of shifting after death. Gilmore and Lucas' interpretations are, generally, accepted now, with Lul's mount changed in 1924. Sophie the Stegosaurus is the most complete known specimen. Sophie is a young adult of indeterminate sex, who reached 5.6 meters (18 feet) long and 2.9 meters (9.5 feet) tall. They are 85% intact and discovered in Wyoming, with 360 bones. In December 2014, it was put on display at the Natural History Museum.

Discovery and species

Marsh's 1891 illustration of S. ungulatus. Note the single row of 12 large rounded plates, based on those of S. stenops, and eight spikes

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. The basis for its scientific name, 'roof(ed) lizard' has been thought to have been Marsh's initial 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. 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.

Valid species

Occurrence data
S. armatus Morrison Formation, Colorado, Wyoming, and Utah, U.S.A. S. stenops Morrison Formation, Colorado, Wyoming, and Utah, U.S.A.

Stegosaurus armatus, meaning "armoured roof lizard", was the first species to be found and is known from two partial skeletons, two partial skulls and at least thirty fragmentary individuals. This species had four horizontal tail spikes and relatively small plates. Up to 9 metres (30 ft) long, it was the longest species within the genus Stegosaurus.

Fossil specimen of Stegosaurus stenops shown as it was found.

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 large, broad plates and four tail spikes. Stegosaurus stenops is known from at least 50 partial skeletons of adults and juveniles, one complete skull and four partial skulls. It was shorter than S. armatus, at 7 metres (23 ft).

Stegosaurus longispinus, meaning "long-spined roof lizard", was named by Charles W. Gilmore and known from one partial skeleton, from the Morrison Formation in Wyoming. Stegosaurus longispinus was notable for its set of four unusually long tail spines. Some consider it a species of Kentrosaurus. Like S. stenops, it grew to 7 metres (23 ft) in length.

Nomina dubia (dubious names)

Stegosaurus ungulatus, meaning "hoofed roof lizard", was named by Marsh in 1879, from remains recovered at Como Bluff, Wyoming. It is known from a few vertebrae and armour plates. It might be a juvenile form of S. armatus, although the original material of S. armatus is yet to be fully described. The specimen discovered in Portugal and dating from the upper Kimmeridgian-lower Tithonian stage has been ascribed to this species.

Stegosaurus sulcatus, meaning "furrowed roof lizard" was described by Marsh in 1887 based on a partial skeleton. It is considered a synonym of S. armatus. 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"), is probably the same as S. armatus. Although named by Marsh in 1887 (including the holotype specimen), the disarticulated bones were actually collected in 1879 by Edward Ashley at Como Bluff, Wyoming.

Stegosaurus seeleyanus, originally named Hypsirophus, is probably the same as S. armatus. Stegosaurus (Diracodon) laticeps was described by Marsh in 1881, from some jawbone fragments. Just as some consider S. stenops a species of Diracodon, others consider Diracodon itself to be a species of Stegosaurus. Bakker had resurrected D. laticeps in 1986, although others note that the material is non-diagnostic and likely synonymous with S. stenops.

Stegosaurus affinis, described by Marsh in 1881, is only known from a pubis and is considered a nomen dubium. It is possibly synonymous with S. armatus.

Reassigned species

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.

Other remains originally attributed to Stegosaurus are now considered to belong to different genera. This is the case for Stegosaurus marshi, which was described by Lucas in 1901. It was renamed Hoplitosaurus in 1902. Stegosaurus priscus, described by Nopcsa in 1911, was reassigned to Lexovisaurus, and is now the type species of Loricatosaurus.

Paleobiology

Stegosaurus at the Field Museum of Natural History.

Stegosaurus was the largest stegosaur, reaching up to 10 meters (33 ft) in length and possibly weighing up to 5,000 kilograms (5.5 short tons). However, 7 to 9 metres was a more usual length. Soon after its discovery, Marsh considered Stegosaurus to have been bipedal, due to its short forelimbs. He had changed his mind however, by 1891, after considering the heavy build of the animal. Although Stegosaurus is undoubtedly now considered to have been quadrupedal, there has been some discussion over whether it could have reared up on its hind legs, using its tail to form a tripod with its hind limbs and browsing for higher foliage. This has been proposed by Bakker and opposed by Carpenter.

Stegosaurus did have very short forelimbs, in relation to its hind legs. Furthermore, within the hindlimbs, the lower section (comprising the tibia and fibula) was short compared with the femur. This suggests that it couldn't walk very fast, as the stride of the back legs at speed would have overtaken the front legs, giving a maximum speed of 6–7 kilometres per hour (4–5 mi/hr).

Mounted skeleton in bipedal posture, Houston Museum of Natural Science

Posture and movement

Soon after its discovery, Marsh considered Stegosaurus to have been bipedal, due to its short forelimbs. He had changed his mind, however, by 1891, after considering the heavy build of the animal. Although Stegosaurus is undoubtedly now considered to have been quadrupedal, some discussion has occurred over whether it could have reared up on its hind legs, using its tail to form a tripod with its hind limbs, to browse for higher foliage.This has been proposed by Bakker and opposed by Carpenter. A study by Mallison (2010) found support for a rearing up posture in Kentrosaurus, though not for ability for the tail to act as a tripod.

Stegosaurus had short fore limbs in relation to its hind limbs. Furthermore, within the hind limbs, the lower section (comprising the tibia and fibula) was short compared with the femur. This suggests it could not walk very fast, as the stride of the back legs at speed would have overtaken the front legs, giving a maximum speed of 15.3–17.9 km/h (9.5–11.1 mph).Tracks discovered by Matthew Mossbrucker (Morrison Natural History Museum, Colorado) suggest that Stegosaurus lived and traveled in multiple-age herds. One group of tracks is interpreted as showing four or five baby stegosaurs moving in the same direction, while another has a juvenile stegosaur track with an adult track overprinting it.

As the plates would have been obstacles during copulation, it is possible the female stegosaur laid on her side as the male entered her from above and behind. Another suggestion is that the female would stand on all fours but squat down the fore limbs and raise the tail up and out of the male's way as he supports his fore limbs on her hips. However, their reproductive organs still could not touch as there is no evidence of muscle attachments for a mobile penis nor a baculumin male dinosaurs.

"Second brain"

A Stegosaurus brain, highlighted in red.

Soon after describing Stegosaurus, Marsh noted a large canal in the hip region of the spinal cord, which could have accommodated a structure up to 20 times larger than the brain. This has led to the famous idea that dinosaurs like Stegosaurus had a 'second brain' in the tail, which may have been responsible for controlling reflexes in the rear portion of the body. It has also been suggested that this "brain" might have given a Stegosaurus a temporary boost when it was under threat from predators. More recently, it has been argued that this space (also found in sauropods) may have been the location of a glycogen body, a structure in living birds whose function is not definitely known but which is postulated to facilitate the supply of glycogen to the animal's nervous system.

Plates

Allosaurus and Stegosaurus skeletons, at the Denver Museum of Nature and Science.

The most recognizable features of Stegosaurus are its dermal plates, which consisted of 17 separate flat plates. 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. In the past, some palaeontologists, notably Robert Bakker, have speculated the plates may have been mobile to some degree, although others disagree. Bakker suggested that the plates were the bony cores of pointed horn-covered plates that a Stegosaurus could flip from one side to another in order to present a predator with an array of spikes and blades that would impede it from closing sufficiently to attack the Stegosaurus effectively. The plates would naturally sag to the sides of the Stegosaurus, the length of the plates reflecting the width of the animal at that point along its spine. His reasoning for these plates to be covered in horn is that the surface fossilized plates have a resemblance to the bony cores of horns in other animals known or thought to bear horns, and his reasoning for the plates to be defensive in nature is that the plates had insufficient width for them to stand erect easily in such a manner as to be useful in display without continuous muscular effort. The largest plates were found over the animal's hips and measured 60 centimetres (2 ft) wide and 60 centimetres tall. The arrangement of the plates has long been a subject of debate but most palaeontologists now agree that they formed a pair of alternating rows, one running down each side of the midline of the animal's back.

Early reconstruction of Stegosaurus with plates lying flat along the back and tail spikes evenly distributed all over the body.

The function of the plates has been much debated. Initially thought of as some form of armour, they appear to have been too fragile and ill-placed for defensive purposes, leaving the animal's sides unprotected. More recently, researchers have proposed that they may have helped to control the body temperature of the animal, in a similar way to the sails of the large carnivorous Spinosaurus or of the pelycosaur Dimetrodon (and the ears of modern elephants and jackrabbits). The plates had blood vessels running through grooves and air flowing around the plates would have cooled the blood. This theory has been seriously questioned, since the closest relative to the common plate-wielding species, Stegosaurus stenops, had low surface area spikes instead of plates, implying that cooling was not important enough to require specialized structural formations such as plates.

Their large size suggests that the plates may have served to increase the apparent height of the animal, in order either to intimidate enemies or to impress other members of the same species, in some form of sexual display, although both male and female specimens seemed to have had them. A study published in 2005 supports the idea of their use in identification. Researchers believe this may be the function of other unique anatomical features, found in various dinosaur species. Stegosaurus stenops also had disk-shaped plates on its hips.

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 mooted over the years:

1. The plates lay flat along the back, like armour. This was Marsh's initial interpretation, which led to the name 'Roof Lizard'. As further and complete plates were found, their form showed that they stood on edge, rather than lying flat.
2. 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 it was thought that they would overlap too much in this arrangement). It was revived, in somewhat modified form, in the 1980s, by an artist (Stephen Czerkas), based on the arrangement of iguana dorsal spines.
3. The plates paired in a double row along the back. This is probably the most common arrangement in pictures, especially earlier ones (until the 'Dinosaur Renaissance' in the '70s). (The Stegosaurus in the 1933 film, King Kong has this arrangement.) However, no two plates of identical size and shape have ever been found within the same animal.
4. Two rows of alternating plates. By the early 1960s, this had become (and remains) the prevalent idea, mainly because the one Stegosaurus fossil with the plates still articulated indicates this arrangement. An objection to it is that this phenomenon is unknown among other reptiles and it is difficult to understand how such a disparity could evolve.

Stegosaurus' plates have a debated function. Marsh suggested they were armour, though Davitashvili (1961) disputed this, claiming they were fragile and ill-placed to suit this. Still, others have defended this theory. Bakker (1986) suggests they were keratinous, having bony cores. Christainsen and Tschopp (2010), studying Hesperosaurus integument, concluded they were coated in a sheath of keratin, strengthening the plate and providing a sharp cutting edge. Bakker states it could flip its osteoderms from side-to-side to present an opponent many sharp spines, having them impeding successful attack. He contends, stating they had an insufficient width for them to easily erect without continuous muscular stress. Plate mobility has also been contended.

Another possible function is thermoregulation, since they sit in such a way similar to Dimetrodon, the ears of rabbits and elephants and Edaphosaurus. The plates had blood vessels that ran through grooves, with air flowing around the plates cooling the blood. Buffrénil, et al. (1986) found "extreme vascularization" in the outermost bone layer, which suggests they were thermoregulatory in use. In 2010, structural comparisons of Stegosaurus plates to alligator osteoderms supports the potential thermoregulation, so this role likely exists.

However, the latter hypothesis has been seriously questioned, since stegosaurus like Kentrosaurus have lesser surface area, suggesting that cooling was not important enough to evolve such an adaptation. It has also been suggested they could absorb sun heat, since a cooling trend towards the Later Jurassic, so a large ectothermic reptile may have increased surface area to absorb solar radiation. Christainsen and Tschopp (2010) state a smooth keratinous covering would have hampered thermoregulation, but it can not be ruled out since cattle and ducks use beaks to expel heat despite their keratinous sheaths. Histological surveys of plate microstructure attribute vascularization for nutrient transportation to match rapid plate growth.

The plates are also thought to have blushed a bright colour when blood pumped into the plates, However, Christainsen and Tschopp (2010) consider this unlikely, since they were made of keratin and not skin. Their size also suggests they could have made the animal taller to intimidate enemies or impress other Stegosaurus. A 2015 study on the shapes and sizes of Hesperosaurus plates suggest they were sexually dimorphic, with wide plates in males and taller plates in females. Christainsen and Tschopp (2010) propose the display function would have reinforced the keratinous sheath, increasing the visible surface, with most horn structures being brightly coloured. Some also suggest they were used to identify the same species, but the use of exaggerated structures in dinosaurs, as a whole, for species identification has been questioned, since nothing like this exists in modern species.

Thagomizer (tail spikes)

Thagomizer on mounted Stegosaurus tail.

A Allosaurus vertebrae injury fitting a Stegosaurus thagomizer.

There has been debate about whether the tail spikes were used for display only, as posited by Gilmore in 1914 or used as a weapon. Robert Bakker noted the tail was likely to have been much more flexible than that of other dinosaurs, as it lacked ossified tendons, thus lending credence to the idea of the tail as a weapon. However, as Carpenter has noted, the plates overlap so many tail vertebrae, that movement would be limited. Bakker also observed that Stegosaurus could have maneuvered its rear easily, by keeping its large hindlimbs stationary and pushing off with its very powerfully muscled but short forelimbs, allowing it to swivel deftly to deal with attack. More recently, a study of tail spikes by McWhinney et al., which showed a high incidence of trauma-related damage, confirms the spikes were indeed used in combat. Additional support for this idea was a punctured tail vertebra of Allosaurus into which a tail spike fit perfectly.

Stegosaurus stenops had four dermal spikes, each about 60–90 centimetres (2–3 ft) long. Discoveries of articulated stegosaur armour show that, at least in some species, these spikes protruded horizontally from the tail, not vertically as is often depicted. Initially, Marsh described S. armatus as having eight spikes in its tail, unlike S. stenops. However, recent research re-examined this and concluded this species also had four.

Growth and metabolism

Juveniles of Stegosaurus have been preserved, probably showing the growth of the genus. The two juveniles are both relatively small, with the smaller individual being 1.5 m (4.9 ft) long, and the larger 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 and coracoid, and the lower hind limbs. Also, the pelvic region of the specimens are similar to Kentrosaurus juveniles. One 2009 study of Stegosaurus specimens of various sizes found that the plates and spikes had slower histological growth than the skeleton at least until the dinosaur reached its mature size.

Partial juvenile Stegosaurus skeleton on display with cast bones at Dinosaur National Monument in Utah

A 2013 study concluded, based on the rapid deposition of highly vascularised fibrolamellar bone, that Kentrosaurus had a quicker growth rate than Stegosaurus, contradicting the general rule that larger dinosaurs grew faster than smaller ones.

A 2022 study by Wiemann and colleagues of various dinosaur genera including Stegosaurussuggests that it had an ectothermic (cold blooded) or gigantothermic metabolism, on par with that of modern reptiles. This was uncovered using the spectroscopy of lipoxidation signals, which are byproducts of oxidative phosphorylation and correlate with metabolic rates. They suggested that such metabolisms may have been common for ornithischian dinosaurs in general, with the group evolving towards ectothermy from an ancestor with an endothermic (warm blooded) metabolism.

Diet

Stegosaurus tooth diagram.

Stegosaurus and related genera were herbivores. However, they adopted a feeding strategy different from that of the other herbivorous ornithischian dinosaurs. 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. they could chew plants). This contrasts with Stegosaurus (and all stegosaurians), which had small teeth having horizontal wear facets associated with tooth-food contact and a jaw probably capable of only orthal movements.

The stegosaurians must have been successful, as they became speciose and geographically widely distributed, in the late Jurassic. Palaeontologists believe it would have eaten plants such as mosses, ferns, horsetails, cycads and conifers or fruits and swallowed gastroliths to aid food processing (due to the lack of chewing ability), in the same manner used by modern birds and crocodiles. Low-level browsing on grasses, seen in 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 hypothesised feeding behaviour strategy considers them to be low-level browsers, eating low-growing fruit of various non-flowering plants, as well as foliage. This scenario has Stegosaurus foraging at most one metre above the ground. On the other hand, 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 metres (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 Stegosauruswere 140.1 newtons (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. However, a 2016 study indicates that Stegosaurus's bite strength was stronger than previously believed. Comparisons were made between it (represented by a specimen known as "Sophie" from the United Kingdom's Natural History Museum) and two other herbivorous dinosaurs; Erlikosaurus and Plateosaurus to determine if all three had similar bite forces and similar niches. Based on the results of the study, it was revealed that the subadult Stegosaurus specimen had a bite similar in strength to that of modern herbivorous mammals, in particular, cattle and sheep. Based on this data, it is likely Stegosaurus also ate woodier, tougher plants such as cycads, perhaps even acting as a means of spreading cycad seeds.

Behavior

Tracks discovered by Matthew Mossbrucker of the Morrison Natural History Museum from Colorado suggest that Stegosaurus lived in multi-age herds. One group of tracks is interpreted as showing four or five baby stegosaurs moving in the same direction, while another has a juvenile stegosaur track with an adult track overprinting it.

Paleoecology

Footprints of an adult and juvenile from the Morrison Formation

Stegosaurus lived in the Morrison Formation during the Late Jurassic. Stegosaurus was likely a grazer, or a forager, eating bushes and other shrubbery. Stegosaurus was attacked and eaten by Allosaurus, Saurophaganax and other carnivores of the Morrison Formation.

Studies say that Stegosaurus likely preferred drier settings than other dinosaurs it lived with, though the environment was semiarid. The Morrison Formation had wet seasons, with spanning floodplains. Stegosaurus likely lived in the forests made out of Brachyphyllum trees, and many other spanning plants.

Cultural Influence

Stegosaurus is among the most recognizable of dinosaurs. It has been depicted in many ways; on film, in cartoons, comics, as children's toys, and as sculpture. It even was declared the State Dinosaur of Colorado in 1982. Stegosaurus is a subject for inclusion in dinosaur toy and scale model lines, such as the Carnegie Collection.

As late as the 1970s, Stegosaurus, along with other dinosaurs, was depicted in fiction as a slow-moving, dim-witted creature. The "dinosaur renaissance" changed the prevailing image of dinosaurs as sluggish and cold-blooded and this re-evaluation has been reflected in popular media.

Science

In September 2002, a hoax poster was presented at the Society of Vertebrate Paleontology entitled "The case for Stegosaurus as an agile, cursorial biped", ostensibly by T. R. Karbek (an anagram of R. T. Bakker) from the non-existent "Steveville Academy of Palaeontological Studies". This was reported in New Scientist magazine, where it was remarked that Stegosaurus was generally believed to be "about as cursorial as a fridge-freezer".

Literature

A sketch of a Stegosaurus forms an important plot point in the opening chapters of The Lost World by Arthur Conan Doyle. Although it is out of print (used copies are available on the Web), Evelyn Sibley Lampman wrote a children's book about twins who find a talking Stegosaurus on their ranch; titled "The Shy Stegosaurus of Cricket Creek".

Sculpture

Sculptor Jim Gary created several, almost-life-sized versions of Stegosaurus. One always was displayed among his traveling exhibition, Jim Gary's Twentieth Century Dinosaurs, and they are frequently used as an illustration of his work in books and articles about the artist because of their distinctive characteristics.

One displayed for months before the electrical engineering research facility at the University of North Carolina at Charlotte during a 2005 campus-wide display of the exhibition, which was hosted by Belk College, became a mascot of sorts to students studying in nearby buildings.

In the movie Howard the Duck, Howard walks under a Jim Gary Stegosaurus when a museum display of the sculptor's work is used as a set for the 1986 film, which was produced by George Lucas.

Cinema

Over the years, Stegosaurus has seen its share of screen time, often pitted in battle against large carnivorous dinosaurs, in both theatres and television. It came up against Ceratosaurus in Journey to the Beginning of Time (1954), in The Animal World (1956), the documentary When Dinosaurs Roamed America (2001),and Jurassic Fight Club where it also faces Allosaurus (2008). It faced Allosaurus in episode two of "Walking with Dinosaurs" (1999), as well as in the special The Ballad of Big Al (2000). It was even seen pitted against Tyrannosaurus, in Planet of Dinosaurs (1978), Walt Disney's Fantasia (1940) (which was the first time use of the spike tail for defense was portrayed), and in the remake of the series Land of the Lost (1992–93). A baby Stegosaurus dubbed Spike is one of the lead characters in The Land Before Time (1988) and its direct-to-video sequels.

In the classic monster film, King Kong (1933), the first creature that the band of rescuers meet, as they chase the abducted Fay Wray deep into Skull Island, is a roaring Stegosaurus, which charges. In the 2005 Peter Jackson remake Stegosaurus is nowhere to be seen, although in the extended edition the fictional Triceratops-like dinosaur "Ferructus" takes its place.

A Stegosaurus also has appeared in The Lost World: Jurassic Park, as one of the first dinosaurs to be seen. They also were seen briefly in Jurassic Park III. (An ailing Stegosaurus is encountered by the characters in the novel Jurassic Park, but was replaced by a Triceratops in the film version.) Although it makes no actual appearance in the film, the name is used; it is on one of the embryo vials stolen (misspelled as 'Stegasaurus').

Stegosaurus is one of the three dinosaur species whose physical characteristics were combined by the designers at Toho, to create the Japanese monster Godzilla; the other two dinosaurs were Tyrannosaurus and Iguanodon. In the American version of King Kong vs. Godzilla this is remarked upon by a reporter, claiming Godzilla was half-Stegosaur, half-Tyrannosaur.

Cartoons and comics

Stegosaurus has been featured in children's cartoons. The Transformers toyline and related television series features four characters which can transform into stegosaurids: Snarl, Slugfest, Saberback and Striker. In the 1980s cartoon Dinosaucers, the character Stego is an anthropomorphic Stegosaurus who while still only a trainee soldier accomplishes difficult tasks despite his inexperience. Also, Stegz was an anthropomorphic stegosaur featured in the series "Extreme Dinosaurs". Ironically, despite the tiny brain size of Stegosaurus, he is portrayed as the most intelligent of the characters in the show. One of the Dino Knights and Drago Clones in Dinozaurs were Dino Stego and his evil counterpart Drago Stegus.

Gary Larson's The Far Side comic strip often used stegosaurs when he showed dinosaurs. The term "Thagomizer" originated as a joke from a Far Side comic strip, in which a group of cavemen in a lecture hall are taught by their caveman professor that the spikes were named in honor of "the late Thag Simmons". The implication is that the Thagomizer was responsible for Thag's death. Whatever the original word for the spiked tail of Stegosaurus was, if it ever had one, has, since the Far Side publication, been replaced by "thagomizer", which is used as a genuine anatomical term by many palaeontological authorities, including the Smithsonian Institution.

JPInstitute.com Description

Easily one of the best known of all the dinosaurs, Stegosaurus is recognized the world over. The unique plates along its back, its small head and spiked tail make it a peculiar and unique dinosaur. This plant-eater evolved to find its food in the low-growing plants of the late Jurassic. The long fearsome spikes on its tail would have made a powerful weapon against predators.

Stegosaurus is often called the dumbest dinosaur because of its incredibly small brain. In fact, most scientists believe that its brain was too small to control such a large creature and that it used an auxiliary "brain" located above its rear legs to help control its movements. This was not actually a brain, but a bundle of nerves that helped relay information from its real brain.

Most fascinating to people are the plates along its back. There has been a great deal of debate about their use and arrangement. The plates were up to 2-feet tall and 2-feet wide (.6 m). The most prevalent theory is that they were used for cooling or heating the animal. A more recent theory, however, suggests that they could have been used as a display during courtship and that they may have been brightly colored. It is also possible that they could move up and down, perhaps to intimidate predators.

The spikes on its tail are also the subjects of some controversy. For years every model of Stegosaurus showed it with the spikes sticking up into the air. It is only since the 1990's that it has become accepted that these spikes stuck out horizontal to the ground, which would have been a potent defensive weapon when swung at a hunter.

Stegosaurus would have lived in family groups and possibly herds, moving slowly through forests while eating the low-growing plants. Its front legs were considerably shorter than its hind legs, making it adapted to nibbling the plants closest to the ground. Stegosaurus is the namesake for a large family of dinosaurs whose members were found all over the world.

Dinosaur Field Guide Description

Stegosaurus ("roofed lizard") is the best-known "plated" dinosaur. It was a favorite food of Allosaurus and has been well studied by paleontologists for over 125 years. It has also been the subject of many false "dinosaur myths". among them that it had a brain no bigger than a walnut (it was, in fact, more than twice as big as a walnut), a second brain in its hips, and plates that could flap on command. Several questions about Stegosaurus have received a lot of study by scientists in the 1990s. It has been proposed at various times that Stegosaurus had either one or two rows of plates along its back. A new specimen found by Ken Carpenter, Bryan Small, and a team at the Denver Museum of Natural History shows that Stegosaurus did have a double row of alternating plates down its back. This new specimen also shows that the tail spikes did not point upward--as in most museum exhibits--but instead pointed sideways.

Fun Facts

Almost everything in popular books about Stegosaurus is based on the specimen at the Smithsonian in Washington, D.C.

Trivia

Stegosaurus comes in two varieties: a large-plated species with four long tail spikes and a rarer, smallen-plated species with shorter tail spikes (possibly eight of them), based on a partial specimen. The second species may not be valid.

Gallery

Appearance in other media

Jurassic Park

• Stegosaurus is been known to have appeared in the Jurassic Park movies. (Except for the first movie).

• Stegosaurus appears in Jurassic World: The Game as a super rare herbivore.

• Stegosaurus appeared in LEGO Jurassic World as an unlockable/playable character.

• Stegosaurus appeared in Jurassic World Evolution and it's sequel, Jurassic World Evolution 2. In this game, they are depicted as having very strict population standards.

Read more Stegosaurus on Jurassic Park Wiki

The Land Before Time

A baby Stegosaurus dubbed Spike is fifth of the main characters in The Land Before Time (1988) and its direct-to-video sequels.

Read more Stegosaurus on Land Before Time Wiki

We're Back! A Dinosaur's Story

Spike is one of the lead characters in the children's book We're Back! A Dinosaur's Story and its sequel, Going Hollywood! A Dinosaur's Dream.

Read more Stegosaurus on We’re Back A Dinosaur’s Story Wiki

Links

http://web.archive.org/web/20040806054348fw_/http://www.jpinstitute.com/dinopedia/dinocards/dc_stego.html#