A variety of horned ceratopsian dinosaurs evolved in the Cretaceous Period of the Mesozoic Era. These well-armored dinosaurs had massive heads equipped with sharp beaks, long pointed horns on the brow and snout, and a bony frill growing from the back of the skull, curving upward to protect the neck and shoulders. The ornamental headgear was used not only for defense, but also for behavioral purposes, including species recognition between herds, establishing territories, and display. They lived in large herds browsing on shrubby low-growing plants and trees, especially adapted to efficiently feed on tough vegetation. Pictured left to right: Styracosaurus, Triceratops, Centrosaurus, Pachyrhinosaurus, and Chasmosaurus.