Assessing the preservation of biogenic strontium isotope ratios (87Sr/86Sr) in the pars petrosa ossis temporalis of unburnt human skeletal remains: A case study from Saba

Rationale: Strontium isotope (87Sr/86Sr) analysis of skeletal remains has become a powerful tool in archaeological studies of human migration and mobility. Owing to its resistance to post-mortem alteration, dental enamel is the preferred sampling material used for 87Sr/86Sr analysis in bioarchaeological provenance research, although recent studies have demonstrated that cremated bone is also generally resistant to diagenesis. This paper presents the results of a pilot study exploring the potential of unburnt petrous bone (pars petrosa) as a reservoir of biogenic (diagenetically unaltered) strontium, as the otic capsule or bony labyrinth within the petrous bone is extremely dense and is thought to be unable to remodel after early childhood, potentially providing an alternative for dental enamel. Methods: From an individual from a colonial-era (18th century) site on the island of Saba in the Caribbean for whom previous enamel 87Sr/86Sr results had indicated non-local origins, multiple locations (n = 4) on the petrous were sampled and measured for strontium isotope composition. Saba (13 km2) has been extensively mapped for baseline strontium isotopes (n = 50) with 87Sr/86Sr varying from ca 0.7065 to 0.7090, whereas enamel 87Sr/86Sr (n = 3) ranged from 0.7104 to 0.7112. Results: All four petrous 87Sr/86Sr ratios (0.7111–0.7122) are consistently and considerably higher than the local bioavailable range, and very similar to the enamel 87Sr/86Sr. These results provide initial evidence that unburnt petrous bones may preserve biogenic strontium, at least in this specific burial context. Conclusions: While more research in diverse burial conditions is needed to validate this observation, if confirmed, it would have broader implications for sample selection strategies in bioarchaeological studies using the strontium isotope method