bones of the skull.

Pachycephalosauria, at one time thought to be close to ornithopods and now known to be related instead to ceratopsians, show a unique skull anatomy that is unlike any other ornithischian. The bones of the top of the skull are thickened and in many taxa expanded significantly to form round bony domes as the top of the head, as well as possessing small nodes or elongate spikes along the back edge of the skull. Many taxa are only known from