Did dome-headed dinosaurs really use their thick skulls to head-butt like bighorn sheep?

Nature · Published 3 October 2026 Swipe more like this →

In short: Pachycephalosaurs are famous for their remarkably thick skull domes, leading to the popular theory that they engaged in combat similar to modern bighorn sheep. However, microscopic analysis of their bone structure suggests these domes were poorly designed to handle such impacts, leaving their true function a persistent mystery.

Pachycephalosaurs, or 'domeheads,' are a rare and relatively poorly understood group of bipedal, herbivorous dinosaurs found primarily in the Late Cretaceous of North America and Asia. Their most striking feature is the significant thickening of the frontoparietal bones in the skull. While this swelling is often interpreted as a protective adaptation for head-butting, microscopic studies indicate that the bone architecture is not well-suited for diverting stress away from the braincase during high-impact collisions.

The diversity of these skull shapes further complicates the combat hypothesis. Pachycephalosaurs exhibit a wide range of cranial designs, from thin, flat tops to pointed ridges adorned with spikes and knobs. This variation suggests that the domes may have served multiple purposes beyond defense or combat. Furthermore, some researchers propose that flat-headed pachycephalosaurs, once classified as distinct species, might simply be the juvenile forms of their dome-headed counterparts. This is mirrored in debates surrounding genera like Dracorex and Stygimoloch, which some studies suggest are merely early growth stages of the larger Pachycephalosaurus.

Because pachycephalosaur remains are often fragmentary—frequently consisting only of isolated skull pieces—taxonomic classification remains difficult. Complete skeletons are exceptionally rare, and many specimens have been misidentified in the past. For example, Majungatholus was once incorrectly grouped with pachycephalosaurs before being reclassified as an abelisaurid theropod. This reliance on cranial characteristics for identification means that our understanding of these animals is constantly shifting as new phylogenetic analyses, such as those by Robert Sullivan, challenge traditional definitions of the group.

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