Study of sequences of dental development and eruption of extant and applicable fossil prosimians, as well as similar data available on Anthropoidea and insectivores, indicates that the ancestral primate stock was characterized by the initial appearance of the anterior dentition, not the molars. From this primitive condition two morphoclines, not one, can be defined with the sharing of derived character states indicating sister-group relationships between Galaginae and Cheirogaleinae and between Lepilemur, Megaladapis, and Adapidae.