Rocker jaws.
Most adult Polynesian mandibles are of the rocker form. Polynesian crania possess a very open cranial base angle and a large upper facial height. The mandibular growth rotations necessary to maintain occlusion in the presence of this cranial morphology lead to development of an exceptionally closed ramus-body angle, with consequent loss of the antegonial notch and appearance of the rocker form.
D000328:Adult; D005147:Facial Bones / Q000033:anatomy & histology; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000033:anatomy & histology*; D009520:New Zealand; D044465:White People