Functional Aspects of Primate Jaw Morphology

The morphology of the face, including the jaws and teeth, varies widely in mammals. This variation is sufficiently correlated with diet so that suites of characters have become identified with dietary preferences. Such characters are used predictively (retroactively?) when the correlations between diet and morphology in modern mammals are extrapolated to the fossil record. Although the higher primates are comparatively homogeneous, the primates as a group have been generally regarded as showing two major trends in the evolution of the craniofacial system: first, the face, including the jaws, becomes ‘shorter’; second the foramen magnum moves from the back to the base of the skull. Although it is tempting to correlate ‘facial shortening’ with a change in diet from insectivory to frugivory or herbivory, modern metrical analysis shows this not to be the case (Radinsky, pers. comm.). Nevertheless the general morphology of the jaw apparatus in herbivorous primates is very different from the long-jawed physiognomy of other herbivores. Similarly, although a progressive shift towards an ‘upright’ feeding and resting posture may be linked with change in foramen magnum position, there is a much closer correlation with increase in brain size (Radinsky, pers. comm.). The net effect, however, regardless of primary cause, has been to change the spatial relationship between the cranium and vertebral column and so affect the function and morphology of the oropharyngeal system. These are just two aspects of the problems of interpretation and explanation to be addressed in accounting for the pattern of primate and particularly hominoid and hominid craniofacial evolution.