Assessing trace element composition in cremated pars petrosa of the human temporal bone through LA-ICP-MS: implications for childhood life-history reconstruction.

A challenge in bioarchaeology concerns the isotopic and trace element analysis of cremated remains for life-history reconstruction. Cremation typically destroys time-resolved key archives such as dental enamel, though the pars petrosa of the temporal bone has emerged as a promising alternative, despite not being deposited in an appositional manner, due to its structural resistance to heat and resilience to diagenetic alteration. Forming within the first two years of life, the pars petrosa can chronologically substitute for dental enamel in childhood reconstructions as it does not remodel throughout an individual’s life, as demonstrated in recent studies. However, the assumption that this structure is resistant to diagenesis and contamination remains undertested and may bias interpretations of mobility, diet, and nursing. This study investigates nine cremated pars petrosa samples using LA-ICP-MS to assess variations in strontium (Sr) and other diagnostic trace elements across different regions of the pars petrosa. The primary aim is to estimate potential differences in elemental concentrations, between the dense, structurally resistant otic capsule and the more porous surrounding external bone areas. Results show that variable Sr concentrations exist within various areas of the pars petrosa and appear associated with diagenetic processes and/or contamination rather than dietary changes related to nursing. While most of the contaminants are easily eliminated in bulk analyses through leaching procedures, the use of high resolution LA based micro-analysis is critical to assess time resolved trace element signals across the pars petrosa. These preliminary findings suggest that the pars petrosa may not be uniformly resistant to post-depositional alteration and that intra-bone variability requires careful consideration. Further investigation and methodological refinement are needed to improve the reliability of isotopic and trace element analyses on pars petrosa samples and enhance reconstructions of childhood stress, diet, and life histories in past populations.