Cranial variables as predictors of hominine body mass.

Body mass is a key variable in investigating the evolutionary biology of the hominines (Australopithecus, Paranthropus, and Homo). It is not only closely related to life-history parameters but also provides a necessary baseline for studies of encephalization or megadonty. Body mass estimates are normally based on the postcranial skeleton. However, the majority of hominid fossils are cranio-dental remains that are unassociated with post-cranial material. Only rarely can postcranial material be linked with cranio-dentally defined hominid taxa. This study responds to this problem by evaluating body mass estimates based on 15 cranial variables to determine whether they compare in reliability with estimates determined from postcranial variables. Results establish that some cranial variables, and particularly orbital area, orbital height, and biporionic breadth, are nearly as good mass predictors for hominoids as are some of the best postcranial predictors. For the hominines in particular, orbital height is the cranial variable which produces body mass estimates that are most in line with postcranially generated estimates. Both orbital area and biporionic breadth scale differently in the hominines than they do in the other hominoids. This difference in scaling results in unusually large estimates of body mass based on these variables for the larger-sized hominines, although the three cranial variables produce equivalent predicted masses for the smaller-bodied hominines.