PhD Dissertations: Christopher John Knüsel, 1991
Biomechanics of the Hominine Cranium with Special Reference to Homo Erectus and the Archaic Homo Sapiens
The adult cranium has traditionally been used to construct hominine phylogenies. This approach, however, disregards the acquired, functional components resulting from cranial growth and development. Such phylogenies are thus open to questions validity. In order to remedy this situation a biomechanical analysis of the cranial first-class lever system was performed to interpret cranial shape, and a series of osteological observations made which identify anterior dental loading as an habitual behaviour of the earliest hominines.
A quantitative analysis employed craniometric measurements of the size, shape, and lengths of the load and lever arms of a series of crania drawn from a mixed hominine cast collection, a very robust Northwest Amerindian sample, and a gracile Calcuttan sample. Statistical comparisons of the attachment area of M. semispinalis capitis demonstrated strong correlations between cranial thickness and the lengths of the load and lever arms.
A photoelastic analysis, which allowed recording of both the magnitude and direction of strains, was carried out to determine how differing cranial shapes influence the transmission of applied forces. The results indicate that the cranial vault of each specimen experiences differential deformation in response to loads of identical magnitude. The Homo erectus cranium demonstrates a unique directional strain pattern different from that of the Cro-Magnon and Skhul crania, whose strain patterns were more similar. The magnitude recording reveal that the Skhul cranium is most well-designed to perform anterior dental loading and Cro-Magnon, the least. The torus occipitalis transversus and occipital bun (chignon) act to prevent transmission of forces to the interparietal portion of the occipital.
It is concluded that the shape of these early hominine crania may be interpreted to result from the commencement of strenuous anterior dental loading at an early age when the greatest impact is made on bone morphology. It is suggested that some of the assumed diagnostic occipital structures used to identify palaeospecies in the hominine fossil record may not be of genetic origin, but rather of an acquired nature, resulting from anterior dental loading and likely other behaviors involving strenuous head movement. This suggests that a re-appraisal of the palaeospecies may be in order.