The ceratopsids, or horned dinosaurs, are well known for their unusual cranial ornamentation, including horns and frills. One of the most famous ceratopsids is Triceratops, named for the two horns over its eyes and the single horn over its nose. For decades, scientists and nonscientists alike have speculated about horn use in Triceratops and its close relatives, with hypotheses including combat between rival males, defense against predators, body temperature regulation, species recognition, and as an aid in knocking down vegetation. This study used scale models of Triceratops skulls to explore positions in which two Triceratops individuals could physically lock horns.

Three possible horn locking positions were found using the Triceratops skull models. Based on this information, predictions were made of where pathologies (injuries) should be found on fossil specimens. Some of these predictions correspond to known pathologies reported in the scientific literature, but it cannot be proven that these injuries were caused during fighting between rival animals.

Triceratops probably had a fighting style very different from that of modern horned mammals, such as sheep, bison, and African antelope. This is mainly due to the vastly different horn orientations—in Triceratops, the horns point up and forward, whereas the horns point sideways or backwards in modern horned mammals. Consequently, head butting or forehead-to-forehead shoving was practically impossible for Triceratops; both behaviors are integral to the fighting styles of many modern horned mammals. However, the fighting styles of some horned chameleons (such as the three-horned Jackson’s chameleon) seem to parallel some of the combat positions inferred for Triceratops.

This study is important for three reasons. First, it shows that it was physically possible for Triceratops (and probably most of its close relatives) to lock horns. However, this work does not prove that horned dinosaurs actually engaged in this behavior. Second, the study makes specific predictions as to where horn-induced injuries should occur on Triceratops skulls. These predictions are testable by looking at fossil material. Finally, this work sets the stage for future work on skull function in Triceratops. By better understanding horn use, and consequently the forces acting upon the skull, we can better comprehend how and why horned dinosaur skulls evolved as they did.