Crown, side and ventral views of a skull of Notharctus, a North American adapoid. Note the open metopic sutures between the frontals in cut 1. This specimen illustrated here has lost the premaxillae with the upper incisors. Cut 2 shows a side view of the lower teeth including four premolars, which is characteristic of adapoid lemurs. Most other primates have only three premolars or fewer above and below. Cut 4 shows frontals of large North American omomyid Hemiacodon.