Oxygen isotopes and the identification of geographical origins: The Valley of Oaxaca versus the Valley of Mexico

Oxygen isotope analysis of human bone phosphate is used for archaeological samples from three sites in Mexico with contemporaneous time sequences to test its usefulness in determining population movement and locational stability. Individuals (N = 11) from the Teotihuacan site of Tlajinga 33 represent an isotopic baseline for the Basin of Mexico from the Early Tlamimilolpa phase (AD 250-300) to the Metepec phase (AD 550-650). The Valley of Oaxaca is represented by 16 individuals from Monte Alban spanning Monte Alban I to Monte Alban V phases (500 BC to AD 1520). These two samples are compared to 11 burials from the site of Tlailotlacan, an enclave of Oaxacan culture at Teotihuacan. The results indicate that there is no temporal variability at any of the sites. Tlajinga and Monte Alban are completely separated isotopically, and the uniformity of δ18O values at both sites indicates few if any itinerant members, thus making the sites good isotopic baselines. There is considerably more variability in the Tlailotlacan sample, however, and its patterning has implications for interpreting the maintenance of ethnicity in the Oaxacan enclave. Although the adults, on average, exhibit the local values of Tlajinga 33, children under the age of 5 have significantly higher δ18O values. Female adults and secondary burials also appear to have higher δ18O values but these subgroups are too small to test statistically.