An Evaluation of Nitrogen Porosimetry as a Technique for Predicting Taphonomic Durability in Animal Bone

To date, direct measurements of bone porosity have been used primarily to quantify the degree of diagenetic alteration. Qualitative zooarchaeological observations over many years have suggested that, for equivalent burial conditions, the bones of different taxa degrade at different rates, and that, even within a single skeleton, systematic variation often occurs. Given that freedom of access of water to the internal bone surface is likely to be an important factor in controlling the rate of chemical alteration, we postulate that the initial porosity of a bone may be an important factor in predicting the rate of degradation. To test this, we have used nitrogen porosimetry as a technique for comparing the total pore volume and size distribution of pores between a selection of anatomical elements taken from a range of modern animals commonly represented on European archaeological sites. We show that the bones of modern domestic pig are, on average, more porous than those of other ungulates, and should therefore be likely to degrade faster after burial. Systematic differences in porosity are also shown between different anatomical elements from a single individual and between adult and juvenile bone. However, we also show that porosity measurements are affected by sample storage and preparation methodology, particularly freezing. Variations in bone porosity between different skeletal elements and taxa necessitate careful sample selection and matching in order to minimize variation. We conclude that, despite these restrictions, direct measurement of variations in bone porosity shows good potential for contributing to a predictive model for bone diagenesis.