With its three sharp horns and spiky head plate, Triceratops horridus must have been an intimidating presence as it trampled across western North America in the late Cretaceous period, some 69 million years ago. Despite its fierce appearance, this famous ceratopsian, or horned dinosaur, was an herbivore.
Triceratops, which is Latin for "three-horned face," was among the last non-avian dinosaurs to evolve before the cataclysmic extinction event that occurred 66 million years ago. One of the most abundant dinosaurs unearthed by paleontologists, Triceratops has been found all across the fossil-rich Hell Creek Formation in northeastern Montana, where rock layers recorded the final millennia of the dinosaurs’ reign. Even so, scientists still have much to learn about Triceratops. (Read about Triceratops with your kids.)
No evidence suggests that Triceratops waged epic battles against Tyrannosaurus rex, but it’s perhaps understandable that popular culture has depicted them this way. The massive Triceratops cut a formidable figure in the prehistoric landscape, stretching up to 30 feet long and weighing six to eight tons. Stout legs helped this quadruped support all that weight as it ambled through the underbrush of North America.
Triceratops’ enormous head might have been all it took to send other dinosaurs running—some recovered skulls measure up to 10 feet long. Its head was ornamented with three horns, a short one above its mouth and two long ones above each eye. Behind these horns was a head frill made of bone and studded with small spikes called epoccipitals.
Scientists continue to debate the primary purpose of this dinosaur’s frill. Early theories that it may have protected Triceratops from predators or acted as a radiator to help the dinosaur regulate its body temperature have been discredited. A 2018 study also ruled out the theory that these frills evolved to help the dinosaurs recognize members of different ceratopsian species.
Today, the prevailing theory is that frills may have helped these dinosaurs select their mates. In 2016, one study found that as Triceratops matured, its head frill ballooned in size, suggesting that it became more important later in life—such as during the sexual selection process.
Fossil evidence has helped scientists decode other aspects of Triceratops behavior. While the frills may not have been intended as a defense mechanism, lesions found on Triceratop skulls reveal that these dinosaurs did sometimes fight one another. And unlike other ceratopsian species, Triceratops fossils are rarely found in groups, suggesting they lived solitary lives.
These herbivores also had beaklike mouths and powerful jaws lined with rows of sharp teeth to shred and grind low-lying vegetation. Evidence suggests that Triceratops teeth were incredibly complex, enabling them to slice through dense vegetation that would have been difficult for other herbivores to consume.
Evolution and extinction
Scientists have long wondered about the evolutionary relationship between Triceratops horridus and its lesser-known relative, Triceratops prorsus. While they had much in common, Triceratops prorsus had a longer nasal horn, a shorter snout, and a more upright top horn. Some paleontologists had theorized that the two species were descendents of an earlier dinosaur, in which case they would have lived at the same time.
But in 2014, a study of more than 50 Triceratops skulls from the Hell Creek Formation found that Triceratops horridus skulls appeared only in the lower layers of rock, while Triceratops prorsus was found only in the upper layers. Skulls in the middle layers had features of both species. This finding suggests that Triceratops horridus evolved into the other species over one or two million years.
No species of Triceratops lived much longer than that. Sixy-six million years ago—about three million years after the dinosaur first appeared—a 7.5-mile-wide asteroid slammed into Mexico’s Yucatán Peninsula. The subsequent environmental catastrophe killed off more than three-quarters of all species on the planet, including Triceratops and its fellow non-avian dinosaurs.