Every dinosaur enthusiast can immediately recognize
In 2004 paleontologist Andrew Farke, who writes the blog The Open Source Paleontologist, used scale models of Triceratops to see if two fighting individuals could effectively lock horns with each other. The models suggested that they could, but Farke needed more evidence that these dinosaurs were actually exhibiting these behaviors. To find these clues Farke teamed up with his colleagues Ewan Wolff and Darren Tanke and looked at the differences between the skulls of Triceratops and another kid of horned dinosaur, Centrosaurus.
The scientists found that both genera of dinosaurs had bone lesions around their frills, but Triceratops had significantly more on the squamosal bone (which makes up the base of the frill). There was no sign that these lesions were caused by disease or by the attack of a predator, but they were consistent with the idea that individual Triceratops fought each other by locking horns. ( Centrosaurus did not have these pathologies, then, because it did not have large brow horns to fight with. If individual Centrosaurus fought each other they would be doing so in a different way.) These dinosaurs still may have used their horns for defense and display, but in Triceratops, at least, there is now evidence that horns played an important role in intraspecies conflict.
As Farke notes in his own summary of the paper, this research raises some interesting questions. Centrosaurus is thought to have evolved from an ancestor with Triceratops-like brow horns. If so, the shift in horn arrangement may have been reinforced by a change in one-on-one dinosaur combat that resulted in fewer injuries.