Primate molar crown formation times and life history evolution revisited

Comparative studies have convincingly demonstrated that the pattern and tim ing of tooth emergence are highly correlated with life-history variables an d brain size. Conversely, a firm relationship between molar formation time and life-history variables has not yet been established. It seems counterin tuitive that one aspect of dental development should be correlated with lif e-history variables, whereas the other should not. In order to shed light o n this apparent discrepancy this study analyzed all data on primate molar c rown formations available in the published literature in relation to life-h istory variables, brain size, and female body mass. Crown formation times w ere found to be particularly highly correlated with both female body mass a nd brain size. Species that depart from the overall brain/body allometry by being relatively large-bodied, e.g., Gorilla gorilla and later Theropithec us oswaldi, also have shorter molar crown formation times than expected. Th e reverse is not found for species that depart from the overall brain/body allometry due to their larger brains, i.e., Homo sapiens. This finding is i nterpreted within an evolutionary and ecological framework. Specifically, b y focusing on ecological commonalities, a scenario is proposed which may al low predictions to be made about the evolutionary history of other extinct primates also. If confirmed in future studies, crown formation time may aga in become a powerful tool in evolutionary enquiry. (C) 2001 Wiley-Liss, Inc .