Stegoceras “Steel Skull” validum

It’s a question we’ve all asked ourselves, watching nature “red in tooth and claw”: Which animal, in all evolution’s bounty, would win in a head-butting fight?

We don’t have to wonder anymore. In a new study, researchers have rounded up the likely contenders for head-butting champ, living or dead, ranging from long-extinct domeheaded dinosaurs to modern-day musk oxen. Since some animals had an obvious advantage, what with being currently alive, the scientists settled for a virtual throwdown. They used CT scans to suss out the precise shape and size of each creature’s noggin, then relied on computer models to see how they’d hold up when the animals went head to head.

Two animals, giraffes and llamas, were knocked out of the competition right away—but they were never really in it. Both animals’ skulls would fracture in a truly aggressive tête-a-tête, the researchers said. Giraffes can, in fact, literally knock each other out if they accidentally butt heads; the stress is simply too much.

Frequent head-butters like the bighorn sheep and musk ox fared much better. The configuration of their skulls—tough outer shell, spongy covering protecting the brain—let them emerge ...