Stegosaurus (-roof lizard') gets its name from big bony plates that jutted upwards from the neck, back, and upper tail. A bony plate probably guarded each hip, and two pairs of spikes stuck out sideways from the end of the tail. As heavy as a big rhinoceros and about the length of a bus, Stegosaurus was the largest known plated dinosaur. It stood more than room-high at the hips and walked on elephantine limbs. Its small head was held low and ended in a toothless, horn-covered beak. Behind the beak were numerous teeth. It is not known if the tail drooped or was held aloft.
Fossil evidence suggests that Stegosaurus roamed wooded plains, browsing on low vegetation. A rival theory suggests that it was a high-level feeder, browsing at heights up to 3.5m (about 12ft), and that it was actually built to rear up. Some evidence lies in the fact that the hind limbs were longer than the forelimbs.
Stegosaurus's tall vertebral spines could have provided enough leverage for the back muscles to be able to lift the weight of the forepart of the body. The supple tail was better suited to being pressed against the ground than the rigid tails of most ornithischlans. In this way, tail and hind limbs could have formed a tripod when a Stegosaurus reared up.
Most dinosaurologists are, however, unconvinced by this theory. Ideas about Stegosaurus's diet, too, have changed over the years. At first, it was thought that the animal had weak teeth and that it used to feed only on soft foods; today, however, this assumption is in some doubt. On the other hand, the narrow snout may indicate that Stegosaurus was a selective feeder and it may have picked out choice items such as seed fern 'fruits' and the fleshy 'flowers' of cycadeoids.
Stegosaurus's spectacular back plates probably helped soak up and shed heat, and rival males may also have used them in harmless threat displays. There were no plates covering the flanks, but a Stegosaurus would have been able to fend off enemies by swishing its tail, or backing into them like a porcupine.
A discovery in 1992 revealed disc-shaped plates protecting the hips, and a pattern of disc-shaped bony studs that shielded the throat.
Diet: Low-growing plants
Size: Length 9m
Weight 2 tonnes
Classification:
Family Stegosauridae
Infraorder Stegosauria
Suborder Thyreophora
Order Ornithischia
Time (million years ago): 150