Triceratops, genus of four-legged, plant-eating dinosaurs (see Dinosaur) that lived during the Cretaceous Period, more than 65 million years ago. Triceratops had three horns on its skull—one on its snout and one above each eye. The name is derived from the Greek words treis, “three”; kerat, “horn”; and ops, “face.” Triceratops was one of the largest horned dinosaurs. The animal’s other defining features include a beak and a neck shield, or frill. Triceratops belonged to a diverse group of ornithischian (“bird-hipped”) dinosaurs called ceratopsians (“horn-face”), which populated North America and Asia toward the end of the age of dinosaurs. Many skulls have been recovered from sediments that floods deposited 67 million to 65 million years ago on low, coastal plains near a seaway that covered the interior of the United States and Canada.

An adult Triceratops was approximately 8 m (26 ft) long and weighed up to 12 metric tons. Skulls of adults were 2.5 m (8 ft) long and ended in a narrow, birdlike beak. Within the beak, its teeth were compressed into rows that resembled large shears. The animal could open its jaws sideways to gather foliage by rotating the joint between its head and neck. Once the food was gathered, the animal then rotated its head back and chopped up the food between its powerful jaws. The underside of the neck frill contained a dense network of blood vessels. Fossil evidence indicates that heat was radiated from the frill through these blood vessels, in much the same way elephants transport blood to their ears to radiate heat. Some scientists believe that Triceratops could gallop like a rhinoceros, but others suggest that the animal was too heavy and clumsy for this.

Skeletal remains of Triceratops have been found over a vast alluvial plain that resembled the modern lowlands bordering the lower part of the Mississippi River near the Gulf of Mexico. The jaws of Triceratops were well suited to reap fibrous plants such as cattails and palmettos, which are known to have grown in that plain. The animal’s large size suggests that Triceratops inhabited an environment with an abundant food supply. Partly healed puncture wounds in their skulls indicate that they fought one another like modern horned mammals, such as male goats and deer. However, some paleontologists believe that Triceratops’ horns may have played a role in species recognition between males and females and in other aspects of social behavior, particularly in group dominance and mating.

A study published in 2006 comparing the skulls of Triceratops at different growth stages supported the notion that the animal’s horns functioned as important social signals in addition to being weapons for self-defense. Paleontologists found that the shape and appearance of the horns and the neck frill provided signs of the animal’s age and sexual maturity. The horns were only about 1 in (2.5 cm) long in babies, then grew longer and curved backward in juveniles. The horns straightened in young adults and finally pointed forward in mature adults. The neck frill also changed as the animals grew older. A set of pointed triangular bones ringed the edge of the frill in juveniles. The shape of these spiky decorative bones gradually flattened as the dinosaurs grew until the bones became almost unnoticeable along the neck frill of mature adults.