Healed scars tag T. rex as predator.

Although Tyrannosaurus rex has a reputation as a fierce predator, the evidence to back up that notoriety has been both rare and debatable. Now, a fossil Triceratops skull with healed bone scars may compel paleontologists to give T. rex its due.

Previously, all of the gnaw marks on bones that have positively identified T. rex as the chewer have shown no sign of healing, says John W. Happ of Shenandoah University in Winchester, Va. It's impossible to tell whether those traces are signs of predation or scavenging. A healed wound would indicate that the intended victim got away from a predator, Happ notes.

The partial skull of a large adult Triceratops unearthed in Montana in 1997 has several wounds that probably were inflicted by a T. rex, says Happ. All of the wounds show signs of infection and healing, an indication that the Triceratops lived for several years after the attack. The outer third of the creature's left brow horn is missing, and cone-shaped indentations on what's left match the tooth tips of a typical large tyrannosaur. Also, Happ says, the 65-millimeter gaps between three deep, parallel serapes on the left side of the skull match the tooth spacing of T. rex, the only meat eater in the ecosystem.