Molar size and diet in the Strepsirrhini: Implications for size-adjustment in studies of primate dental adaptation

Among the Strepsirrhini, molar size does not exhibit a consistent dietary signal when body mass is used to size-adjust molar dimensions. This observation is also true for anthropoid primates, but when postcanine size is expressed relative to the size of the facial skeleton in this clade, folivorous anthropoids tend to have relatively larger postcanine teeth than anthropoids in other dietary categories. The contrast in the results generated by these two independent size variables appears to be related to systematic differences in facial size in the Anthropoidea, particularly between short-faced colobines and long-faced cercopithecines. The goal of this study was to determine whether a similar pattern of relationships characterizes strepsirrhines. Data on molar area, facial size, body mass, and diet for forty-three extant strepsirrhines and seven subfossil lemurs were analyzed using phylogenetic generalized least squares. Results indicate that strepsirrhine folivores tend to have larger molars than frugivores relative to the size of the facial skeleton. Insectivorous species exhibit a wide range of variation in relative molar size that appears to be taxonomically patterned: lorisids in this dietary category resemble folivores, whereas galagids resemble frugivores. These results confirm the generality of the anthropoid pattern and support the idea that, in some contexts, it may be useful to consider elements of the masticatory system relative to their functional and developmental environments rather than to overall organismal size. The biological significance of having large postcanine teeth relative to the size of the face, but not body mass, is discussed with reference to a model that identifies the size of the oral cavity as the most functionally relevant standard for assessing the relative size of the postcanine dentition.