The differential degradation of immature and mature bone in diverse environments: A controlled experiment using pig (Sus scrofa) skeletal remains

Several studies suggest that juvenile skeletal remains are significantly underrepresented in both forensic and archaeological excavations. In archaeological contexts, the disparities between historical burial records and the relative absence of juveniles in cemetery excavations have been a cause for much speculation. The most popular explanation for this paucity in the osteological record is a comparatively rapid breakdown of juvenile bones, due to their smaller size, incomplete mineralization, higher organic and water content, and higher porosity than their adult counterparts. If this holds true, it presents a challenge for accurately identifying skeletonized juveniles in forensic cases. While the idea is widely accepted, few experiments have provided evidence to support it. This study uses infant and sexually mature porcine models to explore the role of bone maturity with regards to: 1) overall susceptibility of the skeleton to biological, physical, and compositional degradation, and 2) the interaction of bone material with different burial environments. The ulnae of immature (2-8 weeks) and mature (6 months) pigs (Sus scrofa) were mechanically defleshed and used as a proxy for human bone of distinct infant and sexually mature groups. Samples (n=200) from both maturity groups were left to degrade in a climate-controlled greenhouse, either buried or on the soil surface. These two varying depositional conditions provide the degradation factors from two different environments. Every month, four bones from each maturity group and environment were collected. Weight loss on ignition analysis was performed on each sample to determine the relative water, collagen, and mineral composition of the bones, and bone weathering analysis was performed to quantify the physical changes of the bone surface. The results of this study indicate that, in the early postmortem interval, immature and mature bone material are differentially affected by their postmortem depositional environment. In both the subaerial and buried environments, the immature bone was found to be more susceptible to compositional degradation, while the mature bone was more heavily affected by physical weathering. It is not known how these initial differences in bone breakdown translate into the long-term survival of immature bone material, however, this study suggests that any interpretations of weathered immature bone, that are based on weathering rates determined by mature bone, should be done so with caution.