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Stegosaurus stenops

Stegosaurus stenops ('roofed reptile') was one of the dominant Late Jurassic plant eating dinosaurs. Stegosaurus roamed the Jurassic woodlands with giant sauropods such as Apatosaurus and Diplodocus while avoiding the ever-hungry Allosaurus. One of this tiny-headed dinosaur's most distinguishing characteristics is the row of diamond shaped plates that ran along its back. These controversial appendages seem now to have been part of the animal's heat regulating system, acting both as heat dissipaters (like the ears of modern elephants) and solar collectors.

Stegosaurs reached lengths of up to 30 feet, weighed 1-2 tons and measured up to 12 feet tall at the highest point on its back. There is some anatomical evidence to suggest that stegosaurs could rear back on their hind legs to browse taller trees. The four long spikes at the end of its tail would ward off predators and were the slow-moving stegosaur's most effect defense.

The earliest stegosaur fossils are from China and come from the Middle Jurassic. By the Late Jurassic, they appear nearly worldwide as stegosaurs reached the apex of their evolutionary history. The Cretaceous decline of stegosaurs is usually attributed to the rise of flowering plants and the dominance of the plant-eating ornithopods.

For such a large animal, Stegosaurus had a very small head. It was long and slender, and hung relatively low to browse vegetation up to a meter above the ground. It is clear from the skull that Stegosaurus was a plant eater. It used the horny beak at the end of its mouth to crop vegetation that was sliced into manageable chunks by cheek teeth before swallowing. These cheek teeth were leaf-shaped with small denticles on their edges. These teeth did not, however, form the dental batteries seen in the ornithopods.

Taxonomy
Stegosaurus is the best known of the stegosaurids. These medium sized (7-9 meters long), plant-eating ornithischians were quadrupedal and are grouped with the Ankylosauria within the Thyreophora.

Anatomy
A Stegosaurus brain had much more in common with the brain of a lizard than with the brain of a mammal. The front of the brain, which included the olfactory bulbs (sense of smell) was unusually large, but the cerebrum (higher thinking) and cerebellum (complex voluntary musclular movement) were quite small. The medulla oblongata (autonomic nervous system) was long and large. An endocast of Stegosaurus displaces about 56 milliliters of water making it very small when compared to the size of the animal. For a fully grown house cat we find that the brain displaces about 30 milliliters of water. In spite of its small brain, stegosaurs were very successful land animals for at least 100 million years.

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