The grooves in the present frill would not have been caused by a fight with another Triceratops, but are the right size and spacing to have come from the teeth of Tyrannosaurus. Evidence like this is rare in the fossil record.
With its three-horned head, the Triceratops is one of the most famous species of dinosaur. They lived at the very end of the Cretaceous Period before the fatal mass-extinction triggered by the asteroid that caused the Chicxulub crater 65 million years ago. These 30-foot long herbivores, weighing 12 tonnes, roamed in an area that is now to the East of the Rocky Mountains in North America, which then had a mild climate. They lived contemporaneously with, and were preyed upon by, Tyrannosaurus rex.