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  1. Isotope ratio analyses of trace elements are applied to tooth enamel, ostrich eggshell, and other archaeological hard tissues to infer mobility and other aspects of hominin and animal paleoecology. It has been assumed that these highly mineralized tissues are resistant to diagenetic alteration, but this is seldom tested and some studies document diagenetic alteration over brief time spans. Here, we build on existing research on Maximum Threshold Concentrations (MTCs) to develop screening tools for diagenesis that can inform heavy isotopic analyses. The premise of the MTC approach is that archaeological tissues are likely contaminated and unsuitable for isotope ratio analysis when they exceed characteristic modern concentration ranges of trace elements. Furthermore, we propose a new metric called the Maximum Threshold Ratio (MTR) of 85Rb/88Sr or whole element Rb/Sr, which can be measured simultaneously with 87Sr/86Sr during laser ablation (LA) MC-ICP-MS or applied during post hoc screening of specimens. We analyzed 56 enamel samples from modern Kenyan mammals and 34 modern ostrich eggshells from South Africa, Namibia, and the United States by solution ICP-MS, as well as a subset of shells using LA-MC-ICP-MS. Our results indicate that thresholds are consistent across taxa at a single location, but likely vary across locations. Therefore, MTCs and MTRs need to be tissue and locality specific, but not necessarily taxon-specific. Other important differences are observed between the inner and outer surfaces of the eggshells and between LA and solution ICP-MS. This exploratory study provides guidelines for building reference thresholds to screen enamel and eggshell for diagenesis potentially impacting biogenic isotope ratios. 
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    Free, publicly-accessible full text available February 1, 2025
  2. null (Ed.)
    Bioarchaeological studies are highly successful in accessing multivalent past social identities. This study applies social identity theory to contexts of violence, developing a theoretical framework to investigate identity-based violence at the Epiclassic (600–900 CE) central Mexican shrine site of Non-Grid 4, where at least 180 individuals were ritually sacrificed and interred. Ethnohistoric and archaeological data indicate that geographic origin was a culturally significant indicator of social difference in pre-Hispanic Mesoamerica. This study therefore reconstructs the residential histories of sacrificed individuals (n = 73), analyzing radiogenic strontium (87Sr/86Sr) and stable oxygen (δ18O) isotopes to consider how the perception of social difference, inferred from geographic origins, contributed to the selection of victims of ritual violence. Biogeochemical results demonstrate that 70% of sampled sacrificed individuals were born and lived their early lives outside of the Basin of Mexico, migrating into the region later in life. In contrast, only 22% of individuals were born and lived in the Basin their entire lives. Observed paleomobility patterns among sacrificial victims thus suggest that they were targeted for identity-based violence based on their divergent geographic origins in the volatile socio-political landscape of the Epiclassic Basin of Mexico. 
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  3. null (Ed.)
    Radiogenic strontium isotopes (87Sr/86Sr) have long been used in analyses of paleomobility within Mesoamerica. While considerable effort has been expended developing 87Sr/86Sr baseline values across the Maya region, work in central Mexico is primarily focused on the Classic period urban center of Teotihuacan. This study adds to this important dataset by presenting bioavailable 87Sr/86Sr values across central Mexico focusing on the Basin of Mexico. This study therefore serves to expand the utility of strontium isotopes across a wider geographic region. A total of 63 plant and water samples were collected from 13 central Mexican sites and analyzed for 87Sr/86Sr on a Thermo-Finnigan Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). These data were analyzed alongside 16 published 87Sr/86Sr values from two additional sites within the region of interest. A five-cluster k-means model was then generated to determine which regions of the Basin of Mexico and greater central Mexico can and cannot be distinguished isotopically using 87Sr/86Sr values. Although the two clusters falling within the Basin of Mexico overlap in their local 87Sr/86Sr ranges, many locations within the Basin are distinguishable using 87Sr/86Sr values at the site-level. This study contributes to paleomobility studies within central Mexico by expanding knowledge of strontium isotope variability within the region, ultimately allowing researchers to detect intra-regional residential mobility and gain a greater understanding of the sociopolitical interactions between the Basin of Mexico and supporting outlying regions of central Mexico. 
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