Stegosaurus

Stegosaurus
File:StegosaurusX.jpg
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 (type) S. stenops S. longispinus

Stegosaurus (pronounced /ˈsteg.əˌsɔː.rəs/) meaning "roof-lizard", referring to the roof-tile-like plates on its back (Greek stego meaning 'plate/roof' and sauros meaning 'lizard') was a genus of large herbivorous, quadrupedal dinosaurs from the Morrison Formation of Upper Jurassic sedimentary rock formations in Wyoming, USA. It is among the most easily identifiable dinosaurs, due to the distinctive double row of kite-shaped plates along the animal's back (the basis for its scientific name) and the long spikes on its tail. Stegosaurus is the State Dinosaur of Colorado.

Stegosaurus shared its world with Allosaurus, Camptosaurus and the sauropods Diplodocus, Camarasaurus and Apatosaurus, other dinosaurs found in the Upper Morrison Formation, which lived 155 to 145 million years ago.

Discovery and species

Originally named by Othniel Charles Marsh in 1877, a number of Stegosaurus species have been identified. However, many of these have been considered by most scientists to be invalid or synonymous with existing species.

• Stegosaurus armatus ("armored roof lizard"): The first species to be found, currently known from two partial skeletons, two partial skulls, and at least 30 fragmentary individuals. This species had eight horizontal tail spikes and relatively small plates. At 9 meters (30 ft), it was the longest species of Stegosaurus.
• Stegosaurus stenops ("narrow-faced roof lizard"): The most well-known species of Stegosaurus, it had large, broad plates and four tail spikes. S. stenops is known from at least 50 partial skeletons of both adults and juvelines, one complete skull and four partial skulls. It was shorter than S. armatus, at 7 meters (23 ft) long. At least one paleontologist (Gilmore) does not consider this a species of Stegosaurus, instead placing it in the genus Diracodon. Others (such as Bakker) disagree.
• Stegosaurus longispinus ("long-spined roof lizard"): Known from one partial skeleton. S. longispinus is notable for its set of four unusually long tail spines. Some consider it a species of Kentrosaurus. Like S. stenops, it grew to 7 meters (23 ft) in length.

Dubious species:

• ?S. ungulatus ("hoofed roof lizard"): Known from a few vertebrae and armor plates; probably the same as S. armatus.
• ?S. sulcatus ("furrowed roof lizard"): Partial skeleton, probably the same as S. armatus.
• ?S. duplex ("two-level roof lizard"): Probably the same as S. armatus.
• ?S. seeleyanus: (originally Hypsirophus). Probably the same as S. armatus.
• ?S. (Diracodon) laticeps: Just as some consider S. stenops a species of Diracodon, others consider Diracodon itself to be a species of Stegosaurus. If this is the case, it is most likely synonymous with S. stenops.

Classification

Stegosaurus was a member of the armored dinosaurs, or Thyreophora, a suborder which includes the ankylosaurs and other stegosaurs, such as Huayangosaurus, Wuerhosaurus, and Kentrosaurus.

Palaeobiology

File:Stegozaur1.png

The size of a Stegosaurus compared to a human

Stegosaurus was the largest stegosaur, reaching up to 12 metres (39.4 feet) in length and weighing up to 5,000 kg (5.5 short tons). However, 7 to 9 metres was a more usual length.

The skull of Stegosaurus was long and narrow and its head was carried close to the ground, probably no higher than 1 metre (3.3 feet), and has been thought it was a browser of low growing vegetation because of this. Stegosaurus had very short forelimbs in relation to its hind legs. It had a small brain, about the size of a walnut.

Plates

The plates of Stegosaurus were highly modified osteoderms, or bony-cored scales, similar to those seen in crocodiles and many lizards today. The largest plates were found over the animal's hips and measured 60 centimeters (2 feet) wide and 60 centimeters tall. The arrangement of the plates has long been a subject of debate but most paleontologists now agree that they formed a pair of alternating rows down the animal's back.

Stegosaurus tooth

The function of the plates is also debated. Their large size suggests that they may have been used to increase the apparent height of the animal, in order to intimidate enemies or to impress other members of the same species. The plates appeared to be too fragile and ill-placed for defensive purposes and both male and female specimens had them. A more recent theory proposes that they may have helped to control the body temperature of the animal, in a similar way to the sail of the large meat-eating Spinosaurus or of the pelycosaur Dimetrodon, also as the ears of elephants and jackrabbits. The plates had blood vessels running through grooves and air flowing around the plates would have cooled the blood. The temperature-control theory has recently been discounted, 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. A study published in 2005 points to a simpler function: identification. Researchers also believe this may be the function of other unique anatomical features, found in various dinosaur species. [1]

Plate Arrangement

One of the major subjects mentioned in books and articles about Stegosaurus is the plate arrangement. The argument has been a major one in the history of how dinosaurs are reconstructed and the entry should have a bit more detail on this point. Four possible plate arrangements have been mooted over the years:

• 1) The plates laid flat along the back, like armor. This was the initial thought by Marsh and why he gave the name 'Roof Lizard'. As more and complete plates were found their form showed that they laid on edge, not along the flat and this arrangement was unlikely.
• 2) The plates were in a paired 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 King Kong has this arrangement.) However, no two plates the same size and shape have ever been found with the same animal.
• 3) Two rows of alternating plates. By the early '60s, this seems to have become (and remains) the prevalent idea, mainly because the one Stegosaurus fossil with plates still articulated indicates this arrangement. An objection to it is that this situation is unknown amongst other reptiles and it is difficult to understand how such a disparity could evolve.
• 4) A single row of plates. One of the original ideas, dropped at some point fairly early on (apparently because it was poorly understood how the plates actually were embeded in the skin, and it was thought that they would overlap too much in this arrangement. It was revived, somewhat modified, in the '80s by an artist (Stephen Czerkas), based on iguana dorsal spines.

(main sources for the above are:

• Edwin Colbert; Dinosaurs, Their Discovery & Their World (1962)
• Stephen Czerkas; "A Reevaluation of the Plate Arrangement on Stegosaurus stenops" in Dinosaurs Past & Present, vol 2 (1987)

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. An interesting 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 2 to 3 feet long. Discoveries of articulated stegosaur armor show that, at least in some species, these spikes protruded horizontally from the tail, not vertically as is often depicted.

There has been debate about the number of spikes S. armatus had in its tail. Marsh described it as having eight but some more recent research questions this, instead hypothesizing that this species may also have had four.

Popular culture

As one of the most recognizable dinosaurs, Stegosaurus has seen its share of screen time.

• 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 behaves like an irritable rhinoceros, and charges. It eventually succumbs to several fusillades of small arms fire.
• Stegosaurus has also appeared in The Lost World: Jurassic Park as one of the first dinosaurs to be seen. (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.
• The Transformers characters of Snarl, Slugfest, Saberback and Striker all had Stegosaurus alternate modes.
• 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 anthromorphic Stegosaurus.
• Gary Larson's The Far Side comic often used stegosaurs when he showed dinosaurs. In one panel (c 1980), cavemen in a lecture hall-type setting are being shown a picture of a stegosaur. The lecturer is pointing to the tail, and the caption reads "And this part is called the thagomizer, after the late Thag Simmons". Since then, the tail spikes have been called 'the thagomizer", occasionally even in a formal palentological setting.
• It appeared in the second episode of Walking with Dinosaurs as a very territorial animal and, as a result, accidentally killing a baby Diplodocus.
• It appears in the Phantom comics as part of the animals living amidst the island surrounded by piranhas.

External links

• [2]
• Stegosaurus "roofed lizard", by T. Mike Keesey at The Dinosauricon.
• Stegosaurus, at DinoData.