How do scientists find out whether Triceratops really fought? One way is to look for damage on its skulls. In a 2009 study of museum skulls, Triceratops had far more lesions, or damaged spots, on a bone of the frill than Centrosaurus, a horned dinosaur with a big nose horn and small brow horns. The study used more than 400 observations, and it found that frill bones were injured about 10 times more often in Triceratops than in Centrosaurus. Its lead author said Triceratops headgear was like a Swiss army knife, used for combat, defense or display. Scientists think Triceratops used its horns to fight other Triceratops.

Skulls also tell how many kinds of Triceratops there were. By 1949, as many as 16 species had been named, because nearly every difference between skulls was treated as grounds for a new species. Scientists today count only two, T. horridus and T. prorsus. T. horridus had a smaller nose horn and a longer beak, while T. prorsus had a longer nose horn and a shorter beak. A 2014 study placed over 50 Triceratops skulls in the rock layers of the Hell Creek Formation and found that the genus changed over time. Over roughly one to two million years at the end of the Cretaceous, it changed from a small nose horn and long beak to a long nose horn and shorter beak.

Teeth and noses give more clues about how it lived. Triceratops teeth wore down while it fed, making a groove called a fuller in each tooth's chewing surface, which cut friction. The teeth grew tightly together in rows called a dental battery, and each tooth had five layers of tissue, more than the four in the teeth of horses and other hoofed mammals. Inside the skull, the nasal space was huge. As of November 2026, University of Tokyo researchers have used CT scans of fossil Triceratops skulls, compared with the snouts of birds and crocodiles, to work out what filled that space.

Young animals add to the picture. In 1997, an amateur fossil hunter found a baby Triceratops skull in Montana's Hell Creek Formation. The skull studied at UC Berkeley likely came from a year-old animal about three feet long. The horns and frill were already there in a baby skull, not just in adults. Baby Triceratops had short, straight brow horns that grew long and curved, and the frill grew bigger compared to the skull as the animal grew up. Scientists think the frill may have helped Triceratops attract mates.

Growth is also at the center of a famous argument. In 2009, Scannella and Horner reported that fossils called Torosaurus may be Triceratops that reached full adulthood before dying. In 2012, Longrich and Field concluded that Torosaurus is a distinct genus of horned dinosaur, not the adult of Triceratops. Researchers coded Torosaurus and Triceratops skulls for traits that change with maturity and used clustering to arrange them into a growth series. You may have read that Torosaurus is simply an old Triceratops. That is not settled, because the scientists still disagree.

Words to know

• lesions: damaged spots
• genus: group of species
• species: kind of animal
• Centrosaurus: another horned dinosaur
• adulthood: grown-up stage