Cranial vault thickness measurement and distribution: a study with a magnetic calliper

Abstract

Cranial vault thickness is a widely studied variable in physical anthropology. However, direct physical measurements are difficult to assess in complete skulls, where the endocranial surface is not easily accessible for standard callipers. Computed tomography represents the best alternative, but is expensive and not always available for many field or museum samples. In this study we present a method for the measurement of cranial vault thickness based on magnetism. We measured bone thickness at 71 points of the vault in 30 human skulls with the use of a portable magnetic calliper, which offers a simple, direct, non-invasive, and cost-effective methodology. Magnetic measures were compared with physical measures sampled with a traditional spreading calliper, and error analysis was assessed. Thickness distribution was evaluated and represented in bidimensional maps after spatial interpolation. The two types of callipers provide the same results, suggesting that the magnetic calliper can be used in those situations in which a traditional calliper is not applicable. In accordance with previously published data, the most variable and thickest bones in our sample were the frontal and the occipital bones, and cranial vault thickness distribution follows a pattern of increasing thickness from lateral regions of the vault to the sagittal plane. The magnetic calliper is a reliable and effective tool to measure cranial thickness in those cases in which the endocranial surface is not easily accessible, and where expensive technology cannot be employed for economic or practical reasons.