Styracosaurus (sty-RACK-oh-SAWR-us) was a herbivorous dinosaur from the Upper Cretaceous Period, about 77 to 74 million years ago.

It had six long horns extending from its neck frill, a smaller horn above each of its eyes and a single horn protruding from its nose, at 60 centimetres (2 feet) long and 15 centimetres (6 inches) wide. It was a large dinosaur, reaching lengths of 5 metres (18 feet) and weighing as much as 3 tons. It stood about 1.8 metres (6 feet) tall. The Styracosaurus possessed four short legs and a bulky body. Its tail was rather short. It also had a beak and flat cheek teeth, indicating that its diet was herbivorous. Styracosaurus probably ate cycads, palms, and other prehistoric plants with its tough beak. It could also chew well with its cheek teeth (like other ceratopsians, but unlike most other dinosaurs).

Like other ceratopsians, this dinosaur was most likely to have been a herd animal, traveling in large groups and caring for its young after they hatched. Evidence of herding behavior exists in the discovery of a bone bed in Arizona, USA with about 100 Styracosaurus fossils.

Styracosaurus was a dinosaur that hatched from eggs and walked on all four short legs. It may have been a relatively fast dinosaur, perhaps running at up to 20 mph (32 kph). Dinosaur speeds are estimated using their morphology (characteristics like leg length and estimated body mass) and fossilized trackways.

When threatened by predators, Styracosaurus may have charged into its enemy like a modern-day rhinoceros does. This would have been a very effective defense.