   #copyright

Stegosaurus

2007 Schools Wikipedia Selection. Related subjects: Dinosaurs

   iStegosaurus

                         Fossil range: Late Jurassic

   Model Stegosaurus, Bałtów Jurassic Park, Poland.
   Model Stegosaurus, Bałtów Jurassic Park, Poland.

                             Conservation status

   Extinct (fossil)
               Scientific classification

   Kingdom:    Animalia
   Phylum:     Chordata
   Class:      Sauropsida
   Superorder: Dinosauria
   Order:      Ornithischia
   Suborder:   Thyreophora
   Infraorder: Stegosauria
   Family:     Stegosauridae
   Genus:      Stegosaurus
               Marsh, 1877

                                   Species

     * S. armatus Marsh, 1877 ( type)
     * S. stenops Marsh, 1887
     * S. longispinus Gilmore, 1914

   Stegosaurus ( IPA pronunciation /ˌstɛgəˈsɔːɹəs/) is a genus of
   stegosaurid armoured dinosaur from the Late Jurassic period (
   Kimmeridgian to Early Tithonian) in what is now western North America.
   Due to its distinctive tail spikes and plates, Stegosaurus is one of
   the most recognisable dinosaurs, along with Tyrannosaurus, Triceratops,
   and Diplodocus. 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 about 81 remains. They lived some
   155 to 145 million years ago, in an environment and time dominated by
   the giant sauropods Diplodocus, Camarasaurus, and Apatosaurus.

   A large, heavily-built and 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 have been the subject of
   much speculation. The spikes were most likely used for defence, 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.
   Enlarge
   The size of a Stegosaurus compared to a human.

   Averaging around 9  metres (30  ft) long and 4 metres (14 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-bodied 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. 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.
   Stegosaurus tooth.
   Enlarge
   Stegosaurus tooth.

   The long and narrow skull was small in proportion to the body. Unlike
   most dinosaurs, it did not have an antorbital fenestra, the hole
   between the nose and eye common to most archosaurs, including modern
   birds, though lost in extant crocodylians. Its 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 apparently did little grinding, as they
   lacked wear surfaces (facets). However, their placement in the jaw
   suggests that Stegosaurus had cheeks.

   Despite the animal's overall size, the braincase of Stegosaurus was
   small, being no larger than that of a dog. A well preserved Stegosaurus
   skull had allowed Othniel Charles Marsh to obtain in the 1880s a cast
   representing the brain of the animal and showed that it 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) has largely contributed to the popular
   old idea that dinosaurs were extremely stupid, an idea now largely
   rejected.

   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.

Classification

   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.

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.

Discovery and species

   Marsh's 1896 illustration of Stegosaurus. Note the twelve dorsal plates
   and eight tail spikes; Stegosaurus actually had 17 plates and just four
   spikes.
   Enlarge
   Marsh's 1896 illustration of Stegosaurus. Note the twelve dorsal plates
   and eight tail spikes; Stegosaurus actually had 17 plates and just four
   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

   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. At
   9 metres (30 ft), it was the longest species within the genus
   Stegosaurus.

   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 both 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 species)

   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.

   Stegosaurus sulcatus, meaning "furrowed roof lizard" was described by
   Marsh in 1887 based on a partial skeleton. 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 nomen dubium. It is possibly synonymous with S.
   armatus.

Invalid 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 Majungatholus, 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 is a synonym of either Hoplitosaurus or Polacanthus.
   "Stegosaurus" priscus, described by Nopcsa in 1911, is a synonym of
   Lexovisaurus.

Palaeobiology

   Stegosaurus was the largest stegosaur, reaching up to 12 metres
   (39.4 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).

"Second brain"

   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
   the 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

   Stegosaurus mounted skeleton and small model at the American Museum of
   Natural History, New York.
   Enlarge
   Stegosaurus mounted skeleton and small model at the American Museum of
   Natural History, New York.

   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. 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.

   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 specialised 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.

Tail spikes

   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. He also observed that
   Stegosaurus could have manoeuvred 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.

   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.

Diet

   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 lacking the wear facets associated with tooth-tooth
   occulsion and a jaw 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.

Popular culture

   As one of the most recognisable dinosaurs, Stegosaurus has been widely
   depicted on film, in cartoons, comics, as children's toys, and has even
   been declared the State Dinosaur of Colorado in 1982. Stegosaurus is a
   popular subject for inclusion in dinosaur toy and scale model lines,
   such as the Carnegie collection. Stegosaurus toys, both plastic and
   plush, are popular among children.

   Sculptor Jim Gary created several, almost-life-sized versions of
   Stegosaurus. One was always displayed among his traveling exhibition,
   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 among a 2005
   exhibition at Belk College of the University of North Carolina at
   Charlotte became a mascot of sorts to students studying in nearby
   buildings. Howard the Duck walked under one when a museum display of
   the sculptor's work was used as a set for the 1986 film of the same
   name which was produced by George Lucas.

   As late as the 1970s, Stegosaurus along with other dinosaurs were
   depicted in fiction as slow-moving, dim-witted creatures. 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".

Cinema

   Over the years, Stegosaurus has seen its share of screen time, often
   pitted in battle against large carnivorous dinosaurs, on both the big
   and small screen. It came up against Ceratosaurus in " Journey to the
   Beginning of Time" (1954), in " The Animal World" (1956) and in the
   documentary " When Dinosaurs Roamed America" (2001). It appeared 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) and in the remake of the series "Land of the Lost"
   (1992-93).

   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 Triceratops-like fictional "Ferructus" takes its
   place.

   Stegosaurus has also appeared in The Lost World: Jurassic Park, as one
   of the first dinosaurs to be seen. They were also 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.

Cartoons and comics

   Dinosaurs are popular amongst children, and Stegosaurus is no
   exception. It is one of the more frequently depicted dinosaurs in
   cartoons. The Transformers television series features four characters
   which can transform into stegosaurids: Snarl, Slugfest, Saberback and
   Striker. In The Land Before Time and its sequels, the character Spike
   is a young Stegosaurus. In the 1980s cartoon Dinosaucers, the character
   Stego is an anthropomorphic Stegosaurus. Also, "Stegz" was an
   anthropomorphic stegosaur featured in the series " Extreme Dinosaurs".
   Ironically, despite the tiny brain size of the Stegosaurus, he was the
   most intelligent of the characters in the show.

   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 honour
   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 indeed ever had one, since the Far Side
   publication the term "thagomizer" has been adopted as a genuine
   anatomical term and is used by multiple palaeontological authorities,
   including the Smithsonian Institution.

   Retrieved from " http://en.wikipedia.org/wiki/Stegosaurus"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
