The intra- and inter-specific variations in dental characters of three forms of Callicebus were studied: C. torquatus, C. moloch and C. personatus. Although the range of variations overlapped extensively in some traits, their frequencies or degree of development were consistently different among them. Thus, the species-level identification among Callicebus may be safely done.
Furthermore, an evolutionary trend of Callicebus was suggested based on the dental morphologies. The trend seems to be represented from the torquatus-type molar to the personatus-type one through the moloch-type's as the succession of morphology. This evolutionary trend was also supported with the result of morphological comparisons between the living Callicebus and the fossil Cebidae monkeys from the middle Miocene.