Reconstructing Middle Horizon mobility patterns on the coast of Peru through strontium isotope analysis

Abstract

The pre-Columbian coastal site of Ancon, Peru frequently has been interpreted as an important outpost of the highland Wari Empire, inhabited by individuals from the sierra and the coast. In order to test this hypothesis, bone-tooth pairs from 35 Middle Horizon (550 AD-1000 AD) Ancon skeletons were analyzed for strontium isotopes, which vary by geologic provenance. Results indicate that 34 of the 35 individuals have 87 Sr/ 86 Sr enamel and bone values higher than Ancon's biologically available strontium isotope range. Nitrogen and carbon isotope data from a subset of the Ancon skeletons suggest that the higher than expected 87 Sr/ 86 Sr values among the Ancon sample likely reflects a diet rich in marine resources rather than migratory activity, and highlight the need to use multiple lines of evidence to track residence change at sites where individuals relied on resources other than locally grown terrestrial foods. The one remaining individual, a young female of elite status, has an enamel strontium isotope signature much lower than the available data for local fauna and soil indicating that she was not raised locally. Her enamel 87 Sr/ 86 Sr ratio fits well within the range of strontium isotope values established for the inland Wari site of Conchopata (Tung, T.A., Knudson, K.J. Social identities and geographical origins of Wari trophy heads from Conchopata, Peru. Current Anthropology, in press.), and suggests that highland, Wari immigrants may have been present at Ancon during the Middle Horizon.