Stegosaurus
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2008-07-16T10:36:39Z
FunkMonk
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Switched model with skeleton in taxobox.
{{Taxobox
| name = ''Stegosaurus''
| fossil_range = [[Late Jurassic]]
| image = Stego fieldmuseum.jpg
| image_width = 250px
| image_caption = Stegosaurus in [[Field Museum of Natural History|Field Museum]]
| regnum = [[Animal]]ia
| phylum = [[Chordate|Chordata]]
| classis = [[Reptile|Sauropsida]]
| superordo = [[Dinosaur]]ia
| ordo = [[Ornithischia]]
| subordo = [[Thyreophora]]
| infraordo = [[Stegosauria]]
| familia = [[Stegosauridae]]
| genus = '''''Stegosaurus'''''
| genus_authority = [[Othniel Charles Marsh|Marsh]], 1877
| subdivision_ranks = [[Species]]
| subdivision =
* ''S. armatus'' <small>Marsh, 1877 ([[type species|type]])</small>
* ''S. stenops'' <small>Marsh, 1887</small>
* ''S. longispinus'' <small>[[Charles W. Gilmore|Gilmore]], 1914</small>
}}
'''''Stegosaurus''''' ({{IPAEng|ˌstɛgəˈsɔrəs}}) is a [[genus]] of [[Stegosauria|stegosaurid]] [[Thyreophora|armoured]] [[dinosaur]] from the [[Late Jurassic]] [[Period (geology)|period]] ([[Kimmeridgian]] to [[Tithonian|Early Tithonian]]) in what is now western [[North America]]. In 2006, a specimen of ''Stegosaurus'' was announced from [[Portugal]], suggesting that they were present in Europe as well.<ref name= "escasoetal06">Escaso, F, Ortega, F., Dantas, P., Malafaia, E., Pimentel, N.L, Pereda-Suberbiola, X., Sanz, J.L., Kullberg, J.C., Kullberg, M.C., and Barriga, F. (2007). "New Evidence of Shared Dinosaur Across Upper Jurassic Proto-North Atlantic: ''Stegosaurus'' From Portugal." ''Naturwissenschaften'',</ref> Due to its distinctive [[Thagomizer|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 [[Ancient Greek|Greek]] {{Polytonic|[[wikt:στέγος|στέγος]]-}}, ''stegos-'' ("roof") and {{Polytonic|[[wikt:σαῦρος|σαῦρος]]}}, ''-sauros'' ("lizard").<ref>{{cite book|author=Liddell & Scott|year=1980|title=Greek-English Lexicon, Abridged Edition |publisher=Oxford University Press, Oxford, UK|id=ISBN 0-19-910207-4}}</ref>
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 155 to 145 [[Mya (unit)|million years ago]], in an environment and time dominated by the giant [[sauropod]]s ''[[Diplodocus]]'', ''[[Camarasaurus]]'', and ''[[Apatosaurus]]''.
A large, heavily built, [[herbivore|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 [[thermoregulation|thermoregulatory]] (heat control) functions. ''Stegosaurus'' was the largest of all the [[stegosauria]]ns (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==
[[Image:Stegozaur1.png|thumb|left|The size of a ''Stegosaurus'' compared to a human.]]
Averaging around 9 [[metres]] (30 [[Foot (unit of length)|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 animal, it was dwarfed by its contemporaries the giant [[Sauropoda|sauropods]]. Some form of [[Armour (zoology)|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.<ref name="Lambert93">{{cite book|title=The Ultimate Dinosaur Book|year=1993|author=Lambert D|pages=110–129|publisher=Dorling Kindersley, New York|id=ISBN 1-56458-304-X}}</ref> 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.<ref name ="Carpenter98">{{cite book|author=Carpenter K|year=1998|chapter=Armor of ''Stegosaurus stenops'', and the taphonomic history of a new specimen from Garden Park Colorado|title=The Upper Jurassic Morrison Formation: An Interdisciplinary Study. Part 1. Modern Geol.|volume=22|pages=127–144}}</ref>
[[Image:Stegosaurus skull Senckenberg.jpg|thumb|''Stegosaurus'' 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 [[archosaur]]s, 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 [[beak#Anatomy|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.<ref name = "FasWeis04">{{cite book|title=The Evolution and Extinction of the Dinosaurs (2nd Edition)|year=2005|chapter=Stegosauria:Hot Plates|editor=Fastovsky DE, Weishampel DB|author=Fastovsky DE, Weishampel DB|pages=107–130|publisher=Cambridge University Press|id=ISBN 0-521-81172-4}}</ref>
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 [[ounce|oz]]) contributed to the popular old idea that dinosaurs were unintelligent, an idea now largely rejected.<ref name =bakker86b>{{cite book|title=The Dinosaur Heresies |year=1986|author=Bakker RT|publisher=William Morrow, New York |pages=365-374}}</ref>
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.<ref>''Stegosaurus''. University of Wyoming Geological Museum. 2006. Retrieved [[October 6]] [[2006]]. [http://www.uwyo.edu/geomuseum/tour/stegosaurus.asp University of Wyoming Geological Museum]</ref> 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.
==Classification==
[[Image:Stegosaurus BW.jpg|thumb|Life restoration of ''Stegosaurus stenops''.]]
''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 [[Armour (zoology)|armoured]] dinosaurs, a suborder which also includes the more diverse [[Ankylosauria|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===
[[Image:Stegosaurus Senckenberg.jpg|left|thumb|Reconstruction of a ''Stegosaurus'' skeleton in the [[Senckenberg Museum]] in [[Frankfurt]].]]
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]].<ref>{{cite book|title=The Armored Dinosaurs|year=2001|chapter=New Primitive Stegosaur from the Morrison Formation, Wyoming|editor=Carpenter, Kenneth(ed)|author=Carpenter K, Miles CA, Cloward K|pages=55–75|publisher=Indiana University Press|id=ISBN 0-253-33964-2}}</ref> 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.<ref>Le Loeuff J, Lockley M, Meyer C, Petit J-P(1999) Discovery of a thyreophoran trackway in the Hettangian of central France. ''C. R. Acad. Sci. Paris'' '''2''' 328, 215–219</ref>
==Discovery and species==
[[Image:Stego-marsh-1896-US geological survey.png|thumb|right|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,<ref name = "Marsh77">{{cite journal|author=Marsh OC|year=1877|title=A new order of extinct Reptilia (Stegosauria) from the Jurassic of the Rocky Mountains|journal=American Journal of Science|volume=3|issue=14|pages=513–514}}</ref> from remains recovered north of [[Morrison, Colorado]]. These first bones became the [[holotype]] of ''Stegosaurus armatus''. The basis for its [[binomial nomenclature|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 [[Roof shingle|shingles]] ([[tile]]s) 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,<ref name ="8spike">{{cite book|title=The Armored Dinosaurs|year=2001|chapter=Othniel Charles Marsh and the Eight-Spiked ''Stegosaurus''|editor=Carpenter, Kenneth(ed)|author=Carpenter K & Galton PM|pages=76–102|publisher=Indiana University Press|id=ISBN 0-253-33964-2}}</ref> 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.<ref name = "Marsh77">{{cite journal|author=Marsh OC|year=1877|title=A new order of extinct Reptilia (Stegosauria) from the Jurassic of the Rocky Mountains|journal=American Journal of Science|volume=3|issue=14|pages=513–514}}</ref> 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''.
[[Image:Stenops.jpg|thumb|left|Fossil specimen of ''Stegosaurus stenops'' shown as it was found.]]
''Stegosaurus stenops'', meaning "narrow-faced roof lizard", was named by Marsh in 1887,<ref name "Marsh87">{{cite journal|author=Marsh OC|year=1887|title=Principal characters of American Jurassic dinosaurs, part IX. The skull and dermal armour of ''Stegosaurus''|journal=American Journal of Science|volume=3|issue=34|pages=413–417}}</ref> with the [[holotype]] having been collected by Marshal Felch at Garden Park, north of [[Cañon City, Colorado|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]]<ref name = "gilmore14">{{cite journal|author=Gilmore CW|year=1914|title=Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus ''Stegosaurus''|issue=89|journal= Series: Smithsonian Institution. United States National Museum. Bulletin 89 |publisher=Government Printing Office, Washington}}</ref> 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)===
[[Image:Como Bluff.jpg|right|thumb|strata at [[Como Bluff]]]]
''Stegosaurus ungulatus'', meaning "hoofed roof lizard", was named by Marsh in 1879, from remains recovered at [[Como Bluff]], [[Wyoming]].<ref>{{cite journal|author=Marsh OC|year=1879|title=Notice of new Jurassic reptiles|journal=American Journal of Science|volume=3|issue=18|pages=501–505}}</ref> It is known from a few [[vertebra]]e and [[Armour (zoology)|armour]] plates. It might be a juvenile form of ''S. armatus'',<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition)|year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H|author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref> 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.<ref name= "escasoetal06">Escaso, F, Ortega, F., Dantas, P., Malafaia, E., Pimentel, N.L, Pereda-Suberbiola, X., Sanz, J.L., Kullberg, J.C., Kullberg, M.C., and Barriga, F. (2007). "New Evidence of Shared Dinosaur Across Upper Jurassic Proto-North Atlantic: ''Stegosaurus'' From Portugal." ''Naturwissenschaften'',</ref>
''Stegosaurus sulcatus'', meaning "furrowed roof lizard" was described by Marsh in 1887 based on a partial skeleton.<ref name "Marsh87">{{cite journal|author=Marsh OC|year=1887|title=Principal characters of American Jurassic dinosaurs, part IX. The skull and dermal armour of ''Stegosaurus''|journal=American Journal of Science|volume=3|issue=34|pages=413–417}}</ref> It is considered a synonym of ''S. armatus''.<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition)|year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H |author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref> ''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''.<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition)|year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H |author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref> 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.<ref>{{cite journal|author=Marsh OC|year=1881|title=Principal characters of American Jurassic dinosaurs, part V|journal=American Journal of Science|volume=3|issue=21|pages=417–423}}</ref> Just as some consider ''S. stenops'' a species of ''Diracodon'', others consider ''Diracodon'' itself to be a species of ''Stegosaurus''. [[Robert Bakker|Bakker]] had resurrected ''D. laticeps'' in 1986,<ref name ="bakker86">{{cite book|title=The Dinosaur Heresies |year=1986|author=Bakker RT|publisher=William Morrow, New York |isbn=0-8217-2859-8}}</ref> although others note that the material is non-diagnostic and likely synonymous with ''S. stenops''.<ref name ="8spike">{{cite book|title=The Armored Dinosaurs|year=2001|chapter=Othniel Charles Marsh and the Eight-Spiked ''Stegosaurus''|editor=Carpenter, Kenneth(ed)|author=Carpenter K & Galton PM|pages=76–102|publisher=Indiana University Press|id=ISBN 0-253-33964-2}}</ref>
''Stegosaurus affinis'', described by Marsh in 1881, is only known from a [[pubis (bone)|pubis]] and is considered a ''[[nomen dubium]]''.<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition)|year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H|author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref> It is possibly synonymous with ''S. armatus''.<ref name = "gilmore14">{{cite journal|author=Gilmore CW|year=1914|title=Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus ''Stegosaurus''|issue=89|journal= Series: Smithsonian Institution. United States National Museum. Bulletin 89 |publisher=Government Printing Office, Washington}}</ref>
===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]]'',<ref>Galton PM (1981) "Craterosaurus pottonensis Seeley, a stegosaurian dinosaur from the Lower Cretaceous of England, and a review of Cretaceous stegosaurs". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 161(1):28–46</ref> 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, is a synonym of ''[[Lexovisaurus]]''.<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition)|year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H|author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref>
==Paleobiology==
[[Image:Scandd0016.jpg|thumb|left|[[Animatronic]] ''Stegosaurus'', Experimentarium, Copenhagen.]]
''Stegosaurus'' was the largest [[stegosauria|stegosaur]], reaching up to 12 meters (39 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.<ref name = "Marsh80">{{cite journal|author=Marsh OC|year=1880|title=Principal characters of American Jurassic dinosaurs, part III|journal=American Journal of Science|volume=3|issue=19|pages=253–259}}</ref> He had changed his mind however, by 1891, after considering the heavy build of the animal.<ref name "Marsh1891">{{cite journal|author=Marsh OC|year=1891|title=Restoration of ''Stegosaurus''|journal=American Journal of Science|volume=3|issue=42|pages=179–181}}</ref>
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.<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition)|year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H|author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref> This has been proposed by [[Robert Bakker|Bakker]]<ref>{{cite journal|author=Bakker RT|year=1978|title=Dinosaur feeding behavior and the origin of flowering plants|journal=Nature|issue=274|pages=661–663|volume=274|doi=10.1038/274661a0}}</ref><ref name ="bakker86">{{cite book|title=The Dinosaur Heresies |year=1986|author=Bakker RT|publisher=william Morrow, New York}}</ref> and opposed by [[Kenneth Carpenter|Carpenter]].<ref name ="Carpenter98">{{cite book|author=Carpenter K|year=1998|chapter=Armor of ''Stegosaurus stenops'', and the taphonomic history of a new specimen from Garden Park Colorado|book=The Upper Jurassic Morrison Formation: An Interdisciplinary Study. Part 1. Modern Geol.|volume=22|pages=127–144}}</ref>
''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).<ref name = "FasWeis04">{{cite book|title=The Evolution and Extinction of the Dinosaurs (2nd Edition)|year=2005|chapter=Stegosauria:Hot Plates|editor=Fastovsky DE, Weishampel DB|author=Fastovsky DE, Weishampel DB|pages=107–130|publisher=Cambridge University Press|id=ISBN 0-521-81172-4}}</ref>
==="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 a ''Stegosaurus'' a temporary boost when it was under threat from predators.<ref name = "FasWeis04">{{cite book|title=The Evolution and Extinction of the Dinosaurs (2nd Edition)|year=2005|chapter=Stegosauria:Hot Plates|editor=Fastovsky DE, Weishampel DB|author=Fastovsky DE, Weishampel DB|pages=107–130|publisher=Cambridge University Press|id=ISBN 0-521-81172-4}}</ref> More recently, it has been argued that this space (also found in [[sauropod]]s) 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]].<ref name = "Giffin90">{{cite journal|author=Buchholz (née Giffin) EB|year=1990|title=Gross Spinal Anatomy and Limb Use in Living and Fossil Reptiles|journal=Paleobiology|volume=16|pages=448–458}}</ref>
===Plates===
[[Image:Stegosaurus 01.jpg|thumb|Front view of a ''Stegosaurus'' skeleton at the National Museum of Natural History.]]
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 [[paleontology|palaeontologists]], notably [[Robert Bakker]], have speculated the plates may have been mobile to some degree, although others disagree.<ref name = "Buff86">{{cite journal|author=Buffrénil|year=1986|title=Growth and Function of ''Stegosaurus'' Plates|journal=Paleobiology|volume=12|pages=459–473}}</ref> 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.<ref name = "Bakker86">{{cite book|author=Bakker, R|year=1986|title=''The Dinosaur Heresies''|pages=229–234|publisher=Penguin Books}}</ref> 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,<ref name = "Marsh80">{{cite journal|author=Marsh OC|year=1880|title=Principal characters of American Jurassic dinosaurs, part III|journal=American Journal of Science|volume=3|issue=19|pages=253–259}}</ref> they appear to have been too fragile and ill-placed for defensive purposes, leaving the animal's sides unprotected.<ref name = "Davitashvili61">{{cite book|title=The Theory of sexual selection|year=1961|author=Davitashvili L|pages=538|publisher=Izdatel'stvo Akademia nauk SSSR}}</ref> More recently, researchers have proposed that they may have helped to control the body temperature of the animal,<ref name = "Buff86">{{cite journal|author=Buffrénil|year=1986|title=Growth and Function of ''Stegosaurus'' Plates|journal=Paleobiology|volume=12|pages=459–473}}</ref> 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.<ref>{{cite journal|author=Farlow JO, Thompson CV, Rosner DE|year=1976|title=Plates of the dinosaur ''Stegosaurus'':Forced convection heat loss fins?|journal=Science|issue=192|pages=1123–1125|volume=192|doi=10.1126/science.192.4244.1123|pmid=17748675}}</ref> This theory has been seriously questioned,<ref>{{cite journal|author=Main RP, Padian K, Horner J|year=2000|title=Comparative histology, growth and evolution of archosaurian osteoderms: why did ''Stegosaurus'' have such large dorsal plates?|issue=20|journal= Journal of Vertebrate Paleontology 56A}}</ref> 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<ref name = "gilmore14">{{cite journal|author=Gilmore CW|year=1914|title=Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus ''Stegosaurus''|issue=89|journal= Series: Smithsonian Institution. United States National Museum. Bulletin 89 |publisher=Government Printing Office, Washington}}</ref> or to impress other members of the same species, in some form of sexual [[Display (zoology)|display]],<ref name = "Davitashvili61">{{cite book|title=The Theory of sexual selection|year=1961|author=Davitashvili L|pages=538|publisher=Izdatel'stvo Akademia nauk SSSR}}</ref> 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.<ref>{{cite web| last = | first = | authorlink = Mayell, H| title = "Stegosaur plates used for identification"| work = | publisher = National Geographic News| date = [[25 May]] [[2005]]| url = http://news.nationalgeographic.com/news/2005/05/0525_050525_stegosaur.html| format = | doi = | accessdate = 2006-10-26 }}</ref> ''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.<ref>{{cite book|title=Dinosaurs: Their Discovery & Their World|year=1962|author=Colbert EH|pages=82–99|publisher=Hutchinson Press, London|id=ISBN 1-111-21503-0}}</ref> The argument has been a major one in the history of dinosaur reconstruction. Four possible plate arrangements have been mooted over the years:
[[Image:Stegosaur.jpg|thumb|Early reconstruction of ''Stegosaurus'' with plates lying flat along the back and tail spikes evenly distributed all over the body.]]
#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.
#By 1891, Marsh published a more familiar view of ''Stegosaurus'',<ref name "Marsh1891">{{cite journal|author=Marsh OC|year=1891|title=Restoration of ''Stegosaurus''|journal=American Journal of Science|volume=3|issue=42|pages=179–181}}</ref> 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),<ref>{{cite book|title=Dinosaurs Past & Present, Vol 2|year=1987|chapter=A Reevaluation of the Plate Arrangement on ''Stegosaurus stenops''|editor=Czerkas SJ, Olson EC|author=Czerkas SA|pages=82–99|publisher=University of Washington Press, Seattle|id=ISBN }}</ref> based on the arrangement of [[iguana]] dorsal spines.
#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.
#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.
===Thagomizer (tail spikes)===
{{main|Thagomizer}}
[[Image:Thagomizer 01.jpg|thumb|Thagomizer on mounted ''Stegosaurus'' tail.]]
There has been debate about whether the tail spikes were used for display only, as posited by Gilmore in 1914<ref name = "gilmore14">{{cite journal|author=Gilmore CW|year=1914|title=Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus ''Stegosaurus''|issue=89|journal= Series: Smithsonian Institution. United States National Museum. Bulletin 89 |publisher=Government Printing Office, Washington}}</ref> 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<ref name ="Carpenter98">{{cite book|author=Carpenter K|year=1998|chapter=Armor of ''Stegosaurus stenops'', and the taphonomic history of a new specimen from Garden Park Colorado|title=The Upper Jurassic Morrison Formation: An Interdisciplinary Study. Part 1. Modern Geol.|volume=22|pages=127-144}}</ref> 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.<ref name ="bakker86">{{cite book|title=The Dinosaur Heresies |year=1986|author=Bakker RT|publisher=william Morrow, New York}}</ref> More recently, a study of tail spikes by McWhinney ''et al.'',<ref>{{cite book|title=The Armored Dinosaurs|year=2001|chapter=Posttraumatic Chronic [[Osteomyelitis]] in ''Stegosaurus'' dermal spikes|editor=Carpenter, Kenneth(ed)|author=McWhinney LA, Rothschild BM & Carpenter K|pages=141–156|publisher=Indiana University Press|id=ISBN 0-253-33964-2}}</ref> 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.<ref>{{cite book|title=The Carnivorous Dinosaurs|year=2005|chapter=Evidence for predator-prey relationships: Examples for ''Allosaurus'' and ''Stegosaurus''.|editor=Carpenter, Kenneth(ed)|author=Carpenter K, Sanders F., McWhinney L.& Wood L|pages=325–350|publisher=Indiana University Press|id=ISBN 0-253-34539-1}}</ref>
''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.<ref name ="8spike">{{cite book|title=The Armored Dinosaurs|year=2001|chapter=Othniel Charles Marsh and the Eight-Spiked ''Stegosaurus''|editor=Carpenter, Kenneth(ed)|author=Carpenter K & Galton PM|pages=76–102|publisher=Indiana University Press|id=ISBN 0-253-33964-2}}</ref>
===Diet===
[[Image:Stegotooth.svg|thumb|left|''Stegosaurus'' tooth.]]
''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<ref>{{cite book|title=The Armored Dinosaurs|year=2001|chapter=Tooth wear and possible jaw action of ''Scelidosaurus harrisoni'' and a review of feeding mechanisms in other thyreophoran dinosaurs.|editor=Carpenter, Kenneth(ed)|author=Barrett PM|pages=25–52|publisher=Indiana University Press|id=ISBN 0-253-33964-2}}</ref> and a jaw probably capable of only orthal movements.<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition |year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H |author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref>
The stegosaurians must have been successful, as they became speciose and geographically widely distributed, in the late Jurassic.<ref name ="dinosauria04">{{cite book|title=The Dinosauria (2nd Edition |year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H|author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2}}</ref> Palaeontologists believe it would have eaten plants such as mosses, ferns, horsetails, cycads and conifers or fruits<ref>[http://www.carnegiemnh.org/exhibits/jurassic/fctsteg.htm ''Stegosaurus ungulatus''] Carnegie Museum of Natural History. Retrieved [[26 October]] [[2006]].</ref> and swallowed [[gastrolith]]s to aid food processing (due to the lack of chewing ability), in the same manner used by modern birds and crocodiles.<ref>[http://www.dinoruss.com/de_4/5c52ddb.htm Stegosaurs] Jacobson, RJ. Dinosaur and Vertebrate Paleontology Information. Retrieved [[26 October]] [[2006]].</ref> Low-level browsing on grasses, seen in modern [[mammal]]ian 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.<ref name = "Weishampel84">{{cite journal|author=Weishampel DB|year=1984|title=Interactions between Mesozoic Plants and Vertebrates:Fructifications and seed predation|journal=N. Jb. Geol. Paläontol. Abhandl.|pages=224–250|volume=167}}</ref> 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.<ref name = "FasWeis04">{{cite book|title=The Evolution and Extinction of the Dinosaurs (2nd Edition)|year=2005|chapter=Stegosauria:Hot Plates|editor=Fastovsky DE, Weishampel DB|author=Fastovsky DE, Weishampel DB|pages=107–130|publisher=Cambridge University Press|id=ISBN 0-521-81172-4}}</ref>
===Behavior===
Recent trackways 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.<ref name="smithsonian08">{{cite journal|last=Rajewski|first=Genevieve|date=May 2008|title=Where Dinosaurs Roamed |journal=Smithsonian |pages=20–24 |url=http://www.smithsonianmag.com/history-archaeology/phenom-dino-200805.html |accessdate=2008-04-30}}</ref>
==Popular culture==
{{main|Cultural depictions of Stegosaurus}}
[[Image:Bałtów Park Jurajski 001.jpg|thumb|Model ''Stegosaurus'', Bałtów Jurassic Park, Poland.]]
One of the most recognizable of all dinosaurs,<ref name = "FasWeis04"/> ''Stegosaurus'' has been depicted on film, in cartoons, comics, as children's toys, and has even been declared the [[List of U.S. state dinosaurs|State Dinosaur]] of [[Colorado]] in 1982.<ref>[http://www.colorado.gov/dpa/doit/archives/history/symbemb.htm Colorado Department of Personnel website - State emblems]</ref>
==See also==
*[[Othniel Charles Marsh]]
*[[Thagomizer]]
{{clear}}
==Footnotes==
{{reflist|2}}
==External links==
{{commons}}
{{Wikibooks|Wikijunior Dinosaurs/Stegosaurus}}
* [http://www.abc.net.au/dinosaurs/fact_files/scrub/stegosaurus.htm Walking With Dinosaurs - ''Stegosaurus'']
*[http://www.foxnews.com/story/0,2933,248979,00.html Europe's First Stegosaurus Boosts Pangaea Theory]
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