Fossils of Triceratops, the best known horned dinosaur, or ceratopsian, are common in western North America.

These four-footed plant-eaters defended themselves with large horns, one above each eye and one above the nostrils. A large frill of bone extended from the back of the skull over the neck, and may have served for display to other members of the species. The snout forms a prominent, sharp-edged beak that was used to crop plants. The fodder would then have been sliced and ground by the tightly packed teeth at the back of the jaws.

There are currently at least 10 species of Triceratops recognized, but these differentiations may not be entirely accurate. What appear to be different species may be males, females, and juveniles of different sizes. However, all Triceratops have a solid frill that is relatively short, unlike dinosaurs such as Torosaurus and Chasmosaurus, which had longer frills with skin-covered openings.