Category: Dinosaur

Stegosaurus (Steg-oh-sore-us) lived in the Late Jurassic of North America. It is the most common ornithscian (bird-hipped) dinosaur from the Morrison Formation, an area in the western United States that has yielded a large amount of dinosaur fossils.



Genera and Species

Thyreophora, Stegosauridae.

Stegosaurus (“Roofed Lizard”)

S. stenops, S. ungulates, S. sulcatus


The rear legs of Stegosaurus were much longer than the front so the animal sloped down to a small head. The 2 m (6 ft) long tail was held up horizontal to the ground and could be swung upwards and sideways.

The most striking feature of Stegosaurus were the armor plates along its back and tail. Their arrangement has been in dispute for decades. Originally, they were placed flat against the back like a turtle’s shell, which led to the name “roofed lizard”. It was later found that the plates stood upright, in two rows that alternated from side to side and were not in a single line. The largest of these pointed plates could be up to two feet high!

There were 2 pairs of spikes on the end of the tail, and these are actually on the sides pointing outwards, rather than standing straight up as previously thought. They may have helped the Stegosaurus protect itself from attacks by predators like Allosaurus and Ceratosaurus.

Additional armor in the form of small rounded, flat bones covered the hips and the throat, and possibly the remainder of the body and tail as well. As with other ornithischians, Stegosaurus has a horny, toothless beak. A pad of spongy tissue beneath the feet helped to support the 2 ton weight. The rear feet had 4 toes, 5 at front, all had hooves. The brain was very small, and a large nerve centre in the hips was originally thought to function as a “second brain” that controlled the rear of the body, though scientists today dispute this theory.


Length 9 m (30 ft).

Weight 1.8 - 4 tons.


Stegosaurus was a low to medium browser. It may have preferred the better watered portions of the Morrison Formation. The plates on back were probably used for display and species recognition, rather than heat exchange or defense as was originally believed.

History of Discovery

Discovered by Othniel Charles Marsh in 1877 and known from hundreds of skeletal remains including fairly complete skeletons. Most have been mature individuals, but in recent years juvenile Stegosaurus skeletons have been discovered.


Found in North America (Utah and Colorado USA) in semi-arid plains with forested rivers with a short rainy season. It shared its environment with sauropods including Brachiosaurus, Apatosaurus, Diplodocus and Camarasaurus, as well as predatory theropods like Allosaurus and Ceratosaurus.


  1. Paul, G. (2016). The Princeton Field Guide to Dinosaurs, 2nd Edition. Princeton, New Jersey: University Press Princeton.
  2. Worth, G. (1999). The Dinosaur Encyclopaedia (pp. 2089). Scarborough, Western Australia: HyperWorks Reference Software.