The name Triceratops means "three-horned face," and the name fits. It had three horns in all. Two long horns were above its eyes and one short horn on its nose. The horns and skull bones were covered in keratin, the material in fingernails. Behind the horns was a bony frill. The frill grew bigger compared to the skull as the animal grew up. Scientists think the frill may have helped it attract mates.

The skull of Triceratops was one of the largest of any land animal. A grown-up one was often at least 6 feet long. At the front was a beak like a bird's. Triceratops walked on four legs. It was a plant-eater. It probably ate low-growing plants. Rows of teeth in the back of its jaws cut up tough plants. The teeth grew tightly together in rows called a dental battery.

Triceratops lived in North America, about 68 to 66 million years ago. Tyrannosaurus rex lived at the same time and place. Many Triceratops fossils have been found in Montana's Hell Creek rocks. It is one of the most common dinosaurs found as fossils. Othniel Charles Marsh named Triceratops in 1889. At first he thought the horn bones belonged to a giant bison. Two species are counted today, T. horridus and T. prorsus. Scientists think Triceratops died out with all the other non-bird dinosaurs, after an asteroid hit near Mexico.

So what were the horns for? You may have heard that Triceratops used them mainly to fight Tyrannosaurus. In fact, scientists think Triceratops used its horns to fight other Triceratops. They also think it may have used its horns against predators such as Tyrannosaurus. Triceratops fossils are usually found one at a time, which suggests many lived alone. Young ones had short, straight brow horns. As they grew up, the horns grew long and curved.

Words to know

• keratin: fingernail stuff
• frill: bony neck shield
• battery: tight row
• predators: animals that hunt