With its rock-hard horns, shieldlike head plate, and massive torso, Triceratops horridus —"three-horned face"— must have been an intimidating presence in the late Cretaceous period. But this giant was an herbivore, preying only on the vegetation of western North America. Fossil evidence shows that Triceratops was about 30 feet (9 meters) long and 10 feet (3 meters) tall and weighed 4 to 6 tons. Stout limbs supported Triceratops's girth, but it was unlikely the dinosaur could move very quickly. Like a modern-day rhinoceros, Triceratops probably spent much of its time grazing on plant matter. It used its beaklike mouth and powerful jaws lined with rows of sharp cheek teeth to shred and grind cycads, ferns, and other low-lying vegetation. Triceratops's head was its most imposing feature. It measured 4 to 5 feet (1.2 to 1.5 meters) across and was ornamented with impressive horns and a head plate. It used its horns—a short one above its mouth and two long ones above its eyes—to charge predators, such as T. rex. They likely were also used in mating rituals. Behind its horns was a 6-foot-wide (1.8-meter-wide) head frill made of bone. Scientists aren't sure what purpose the frill served. It may have protected the dinosaur's neck from predators. Like a peacock's splayed plumage, it may have attracted mates in mating rituals. It may have acted as a radiator, helping Triceratops regulate its body temperature. This ceratopsian, or horned dinosaur, was one of the last dinosaurs in the late Cretaceous period. It lived just before the Cretaceous-Tertiary extinction 65 million years ago.