Digital photodensitometry: a reliable and accessible method for measuring bone density

Abstract

Taphonomic analyses are frequently reliant on bone structural density data, which are used as a proxy measure of bone strength. Methods used to obtain these data are often either destructive, or expensive. Consequently the data available tend to be based on only a small number of animals. A method that can measure the bone density of a large number of animals at a comparatively low cost is therefore desirable. This paper sets out such a method, based on photodensitometry. Bones are radiographed, the images are converted into digital files, standardised, and their optical density measured. These data are combined with metrical information to produce a measurement that relates to a specimen's bone density. The method is shown to be repeatable and comparable to (or perhaps better than) Dual Energy X-ray Absorptiometry (DEXA) in terms of accuracy. It also does not suffer from the methodological problems regarding the cross-sectional area of the specimen that are associated with DEXA. Density data produced by the method described here have successfully been used in a taphonomic analysis of the faunal assemblage from the site of Çatalhöyük, Turkey, shedding light on the use of different types of space by the ancient inhabitants of the site. The same data have cast doubt on the common assumption that the bone density of modern animals can act as an analogue for that of archaeological animals.