Triceratops
There has been much speculation over the functions of Triceratops''' head adornments. The two main theories have revolved around use in combat, or display in courtship, with the latter thought now to be the most likely primary function.Triceratops were long thought to have used their horns and frills in combat with predators such as Tyrannosaurus. The idea was discussed first in 1917 and again 70 years later by Robert Bakker.Sternberg C.H. 1917. Hunting dinosaurs in the badlands of the Red Deer River, Alberta, Canada. San Diego, California. There is evidence that Tyrannosaurus did have aggressive head-on encounters with Triceratops, based on partially healed tyrannosaur tooth marks on a Triceratops brow horn and squamosal; the bitten horn is also broken, with new bone growth after the break. Since the Triceratops wounds healed, the Triceratops survived the encounter. Tyrannosaurus is also known to have fed on Triceratops. Evidence for this includes a heavily tooth-scored Triceratops ilium  and sacrum.