The size of a Stegosaurus compared to a humanStegosaurus tooth
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Stegosaurus (STEG-o-sawr-us) meaning "plated lizard", because of the plates on its back (Greek stego = plate/roof + sauros = lizard) was a genus of large herbivorous dinosaurs from the Upper Jurassic of North America. more...

Tyrannosaurus Rex  Tyrannosaurus Rex

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 four long spikes on its tail (referred to as the thagomizer).


Stegosaurus was the largest stegosaur, reaching up to 12 meters (40 feet) in length and weighing up to 5,000 kg (5.5 short tons). However, most specimens never exceed 7 meters (23 feet) and 2,000 kg (2 short tons).

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.

The purpose 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 species. However, the plates were 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 temperature of the animal, much as elephants and jackrabbits do with their ears. The plates had blood vessels running through grooves and wind 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 purpose: identification. Researchers also believe this may be the purpose behind other unique formations found in various dinosaur species. The tail appears to have acted as a weapon. Its tail included four spikes, each about 2 to 3 feet long, an arrangement known as a thagomizer.

The skull of Stegosaurus was long and narrow, and its head was carried close to the ground, probably no higher than 1 meter (3 feet). Stegosaurus had a small brain, about the size of a walnut.


Stegosaurus was a member of the armored dinosaurs, or Thyreophora. Its relatives include Ankylosaurus and Nodosaurus.

In film

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 succombs 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.


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