Stegosaurus was the largest member of the dinosaur family named Stegosauridae. It was a quadruped, herbivore dinosaur that lived during the Early Cretaceous period, about 140 million years ago. Stegosaurus was discovered in 1877 by Professor Othniel Marsh. When the specimen was unearthed, it had large, bony plates on its back, which reminded him of roof tiles. This is how Stegosaurus received its name, which means “roofed lizard”. Some of the bony plates were over 3 feet high, but it is still a mystery how the plates were positioned on its body and what they were used for. There are different ideas in the scientific community as their usage; some believe that they may have assisted the dinosaur with thermoregulation. Another idea is that the plates helped Stegosaurus to defend itself from predators attack by having them positioned flat on its back. There is speculation that these plates may have been brightly colored and were used as displays to attract females. Stegosaurus was a large, and heavy quadruped dinosaur, it was also slow-moving. Instead of running away it had to stay in one place and defend itself against predators. Its best defense was its powerful tail, which had a set of four bony spikes at the end. Some species had two pairs of spikes, while others had four pairs. It is believed by some researchers that Stegosaurus was not able to coordinate a striking tail blow with its tail very well since its brain was so little. Perhaps the dinosaur was only able to thrash around its tail wildly when faced with an attack from dinosaurs such as Allosaurus.
Some writers thought Stegosaurus was stupid because it had a small head and brain. This idea seems to be the beginning of the belief that all dinosaurs were dimwitted, slow, and stupid. Because Stegosaurus had a small brain, some scientists believed it had a secondary brain in its hip region. The brain of Stegosaurus was just the right size for its body and lifestyle. After all, stegosaurs lived for millions of years. The enlargement in the hip region was not brain tissue, but a complex nerve center called the "sacral plexus." It was a secondary control center for the spinal cord. Stegosaurus may have lacked intelligence, but not all dinosaurs were stupid. Most others had larger brains and were possibly capable of more complex mental processing. The front legs of Stegosaurus were only half as long as the heavy rear legs, but they were stout and well suited for carrying the weight of the front of the body. The feet were short and stubby, with four blunt toes on the front feet and three toes on the rear feet. The difference in size between the front legs and rear legs shows the bipedal (two-legged) ancestry of Stegosaurus. Scientists have often wondered why these animals had bony plates. The plates were covered with skin that had many blood vessels in it. The blood would have released heat if the animal was too warm and taken heat from the sun to warm the animal if it was cold. Others argue that the plates were for protection from predators or from coarse vegetation, much as the bony armor of armadillos protects them from predators and plants that would pierce their skin. Some scientists think that the plates were for display in combat or when faced with an enemy. These plates made them look twice as large as they were. Perhaps all these ideas are correct.