The Triceratops Only Had Two Horns.

Triceratops

About 65 million years ago, just before the K-T extinction that wiped out the dinosaurs, the Triceratops occupied the marshes and forests of western North America. 

Triceratops is Greek for "three-horned face," but this dinosaur actually had only two horns. The shorter "horn" on the end of its snout was made from a soft protein called keratin, the kind found in human fingernails. 

The triceratops enormous skull had a backward-pointing frill that could get up to seven feet in length. Males with bigger heads were more attractive to females during mating season and passed down this trait to their offspring. It may also have had some temperature-regulation function.

The Triceratops had birdlike beaks and "batteries" of shearing teeth embedded in their jaws, a few hundred of which were in use at any given time. As one set of teeth wore down from constant chewing, they would be replaced by the adjacent battery.

It is the largest of the horned dinosaurs and it is believed that fully grown, the Triceratops were about 26 ft in length, 10ft in height and weighed anywhere between 6 to 12 tons.

During the late Cretaceous period, they had evolved to the size of cattle, but their distant ancestors were small and occasionally walking on two legs as they roamed central eastern Asia. 

The first known Triceratops fossil to be found were horns attached to a partial skull, found near Denver, Colorado in 1887.

Some paleontologists argue that the the two-horned Torosaurus was really unusually long-lived Triceratops males whose frills continued to grow into old age.

The US state of Wyoming lists the Triceratops as its state dinosaur.