Fine-scaled oxygen isotope variation in tooth enamel: milk does not trump seasonality

Oxygen isotope compositions (􀈽18O) in tooth enamel are of considerable interest in bioarcheology and paleoanthropology for their reported relationship to milk intake during infant nursing as well as seasonal variation due to meteorological cycles. In 2018 we presented near-weekly 􀈽18O values measured with the Sensitive High Resolution Ion Microprobe – Stable Isotopes (SHRIMP-SI) over the 􀜪rst 2.75 years of life in a Neanderthal 􀜪rst molar (M1) that showed strong annual trends and maximum 􀈽18O values long after exclusive milk intake. These results suggested that hypothesized isotopic enrichment due to milk intake is minor at best, and does not hinder paleoenvironmental reconstructions. Here we report SHRIMP-SI 􀈽18O values prior to, during, and after nursing in 10 nonhuman primate dentitions (4 wild baboons, 6 captive macaques). Comparisons of M1s with successively-forming teeth reveal maximum 􀈽18O values after species-typical ages for cessation of suckling (weaning) in 5 of 6 individuals. We also 􀜪nd short term 1-2 per mil 􀈽18O 􀜫uctuations within a few weeks of physiological disruptions including birth (7 of 9 individuals) and severe illness (4 of 4 individuals) 􀀠 these shifts in tooth chemistry are similar in magnitude to previous inferences of human nursing cessation and prehistoric environmental variation from coarsely-drilled bulk samples. Reported 􀈽18O decreases in bulk sampled serially- forming human teeth may be due to natural variation in environmental water sources rather than the cessation of isotopically enriched mothers’ milk. Ongoing elemental studies will further clarify the determinants of 􀈽18O variation and instill greater con􀜪dence in environmental reconstruction from primate dentitions. ; No Full Text