Stegosaurus (roof or plated lizard) was a species of large herbivorous dinosaurs from the Upper Jurassic of North America. It is in the middle of the most easily identifiable dinosaurs, due to the characteristic double row of kite-shaped plates along the animal's back (the basis for its scientific name) and the four extended spikes on its tail (referred to as the thagomizer).
Stegosaurus was the main 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 go beyond 7 meters (23 feet) and 2,000 kg (2 short tons).
The plates of Stegosaurus were highly customized osteoderms, or bony-cored scales, similar to those seen in crocodiles and a lot of lizards today. The largest plates were found over the animal's hips and measured 60 centimeters (2 feet) wide and 60 centimeters tall. The agreement of the plates has long been a subject of debate, but most paleontologists now agree that they shaped a pair of alternating rows down the animal's back.
The reason of the plates is also debated. Their huge size suggests that they may have been used to increase the obvious height of the animal in order to intimidate enemies or to impress other members of the species. However, the plates were easily broken and ill-placed for suspicious purposes, and both male and female specimens had them. A more new theory proposes that they may have helped to control the hotness of the animal, much as elephants and jackrabbits do with their ears. The plates had blood vessels running from side to side grooves and wind flowing around the plates would have refrigerated the blood.
The temperature-control theory has recently been discounted, since the closest relative to the ordinary plate-wielding species, Stegosaurus stenops, had low surface area spikes instead of plates, implying that cooling was not significant enough to require particular structural formations such as plates. A study in print in 2005 points to a simpler purpose: identification. Researchers also consider this may be the purpose behind other unique formations establish in various dinosaur species. The tail appears to have acted as a weapon. Its tail built-in four spikes, each about 2 to 3 feet long.
The skull of Stegosaurus was extended and narrow, and its head was approved
close to the ground, almost certainly no higher than 1 meter (3 feet).
Stegosaurus had a small brain, about the size of a walnut