The name Triceratops means "three-horned face," and even the young had a horned face. The horns and frill were there in a baby skull, not just in adults. At first, a young one had short, straight brow horns. They grew long and curved as the animal grew up. The frill grew bigger compared to the skull. The horns and skull bones were covered in keratin, the material in fingernails. Triceratops and its young may also have been colorful, like the birds that came from dinosaurs.

Scientists today count two species of Triceratops, T. horridus and T. prorsus. Every Triceratops had two long horns above its eyes and one short horn on its nose. The two species differed in the nose horn and the beak. T. horridus had a smaller nose horn and a longer beak. T. prorsus had a longer nose horn and a shorter beak. Othniel Charles Marsh named Triceratops in 1889. He first thought the horn bones belonged to a giant bison. The skull he used to name it belongs to Yale's Peabody Museum of Natural History.

Triceratops was a plant-eater, and 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. Each tooth had five layers of tissue. That is more than the four layers in the teeth of horses and other hoofed mammals. The skull was one of the largest of any land animal, and a grown-up skull was often at least 6 feet long.

Triceratops lived in North America, about 68 to 66 million years ago. It is one of the most common dinosaurs found as fossils. Many have been found in Montana's Hell Creek rocks, and some in what is now Colorado. In August 2017, a construction crew in Thornton, Colorado, found a Triceratops. Tyrannosaurus rex lived at the same time and place. Scientists think Triceratops died out with all the other non-bird dinosaurs, after an asteroid hit near Mexico.

What were the horns for? Scientists think Triceratops used its horns to fight other Triceratops. It may also have used its horns against predators such as Tyrannosaurus. Its fossils are usually found one at a time, which suggests many lived alone. The frill may also have helped it attract mates. So the head of a Triceratops may have had more than one use.

Words to know

• species: kind of animal
• keratin: fingernail stuff
• battery: tight row
• predators: animals that hunt
• asteroid: space rock