Correspondence between stable carbon, oxygen and nitrogen isotopes in human tooth enamel and dentine: Infant diets at Kaminaljuyu
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abstract
We have previously shown that records of the history of dietary supplementation and weaning can be recovered from isotopic analyses of enamel carbonate in permanent human teeth which form during early childhood. Here, we describe a parallel and complementary record of dietary change in the 13C and 15N composition of dentine collagen from the same teeth (a first permanent molar, M1; a premolar, P; a third molar, M3), which are from the archaeological site of Kaminaljuyu, in highland Guatemala. In this smaller sample, enamel 13C and 18O show the same patterns that we described previously (Wright and Schwarcz, 1998). Enamel 13C increases from M1 to P and M3, owing to the introduction of solid foods to the milk diet by 2 years of age. Enamel 18O decreases from M1 and P to M3 owing to a reduced intake of 18O-rich breast milk at an older age, perhaps 4 years. Although limited in scope by the poor preservation of dentine at this site, we observed that first molars, which are first to form, show higher dentine 15N than do teeth developing at older ages, paralleling the pattern that has been described for bone collagen of deceased children. For most individuals, this drop occurs early, owing to the introduction of solid protein foods before 2 years of age. Dentine 13C shows two widely divergent intertooth patterns. Some individuals show an increase in later developing teeth, a pattern which parallels the enamel 13C data. Others show a decline in dentine 13C, suggesting a shift to an isotopically lighter protein source in later childhood. Despite these divergent trends, differences in 13C between enamel and dentine are significantly greater in teeth developing in later childhood (P, M3) than in those forming in infancy (M1), a trend which appears to be a trophic effect, but is largely determined by enamel 13C. Together, the use of enamel and dentine isotopic ratios allows greater precision for reconstructing the culturally variable nature of the dietary shift from breast milk through complementary feeding and weaning to an adolescent diet.
