Stegosaurus

Perhaps the largest of the stegosaurs, Stegosaurus(roof lizard) is also one of the most famous dinosaurs. This large herbivore roamed across North America and perhaps Europe roughly 145-155 million years ago.

Description
Stegosaurus was an odd dinosaur. It had a small head compared to it's huge body. This dinosaur also sported 3 foot(1 meter) long spikes at the end of its tail that it probably used for defense and seventeen plates on its back. The front legs of Stegosaurus were also shorter than it's back legs, meaning it had a low feeding range.

Size
A number of good skeletons of Stegosaurus have been unearthed. They show a somewhat broad range in terms of size, but all are large. The smallest adult individuals measure at least 20 feet(6 meters) long and would have weighed about 2 tons in life. The biggest exceed 30 feet(9 meters) in length and would have weighed close to 4 tons. Most averaged about 23-26 feet(7-8 meters) long and weighed roughly 3 tons.

Plates and Tail Spikes
The exact function of the plates is not known. Thermoregulation is one of the most common theories. It was once thought they were for defense against predators, but many feel they would have offered poor protection. Display is another common line of thinking. The tail spikes however, are clearly weapons. They are designed to punch a hole in the animals attacker so that it may easily escape.

Predators and Behavior
Stegosaurus lived in a world of predators. Large hunters were everywhere. Allosaurus was the most common large theropod and dozens of fossils show injuries inflicted on both species. This suggests frequent interaction. Other big hunters like Ceratosaurus and Torvosaurus would have posed a threat as well. Most fossils of Stegosaurus suggests a solitary life, although it's possible they got together in herds from time to time.

Brain
Stegosaurus has one of the smallest brain to body ratios of any dinosaur, or animal for that matter. It's brain was only a little bit bigger than a golf ball, compared to a body the size of an elephant. This animal probably relied heavily on instinct.

In Popular Culture
With its distinct look, Stegosaurus has been featured heavily in the media. A number of movies have featured it like The Lost World: Jurassic Park and Disney's Fantasia. Documentaries like Walking Wtih Dinosaurs and Planet Dinosaur also depicted the animal. Stegosaurus has also been featured in many books and video games.