Evidence of Combat in Triceratops

"Evidence of Combat in Triceratops," PLoS ONE

Combine this with the possibility of cloning extinct creatures and life gets more interesting all the time:

"This pattern is consistent with Triceratops using its horns in combat and the frill being adapted as a protective structure for this taxon. Lower pathology rates in Centrosaurus may indicate visual rather than physical use of cranial ornamentation in this genus, or a form of combat focused on the body rather than the head."