Isotopic Values of Prenatal Development: δ 13C and δ 15N Variation in Early‐Formed Human Tissues

ABSTRACT Objectives Carbon (δ 13C) and nitrogen (δ 15N) isotope analysis illuminates diet and physiology in the past, yet interpretation is complicated by development and tissue‐specific collagen formation. This study tests whether systematic isotopic offsets occur between auditory ossicles, deciduous dentin, long bones, and ribs in individuals who died as perinate, neonate, or young infants, and assesses implications for reconstructing maternal diet and early‐life physiology. Materials and Methods Collagen δ 13C and δ 15N were measured for 106 samples from 27 individuals recovered from five sites spanning the Early/Late Iron Age, Early Roman, and 17th–19th centuries. Results Results reveal a consistent δ 15N trajectory: values generally increase from ossicles to teeth and decrease from teeth to long bone/rib. Tooth–long bone/rib δ 15N offsets are significant across the sample and within each age group. δ 13C shows a modest, systematic increase from ossicle to tooth; ossicles are significantly lower than long bones/ribs and tooth, whereas tooth to long bone/rib δ 13C exhibits no uniform group‐level offset. These systematic patterns cannot be explained by maternal dietary variation across time and sites and instead reflect developmental physiology. Discussion These findings indicate that, in perinates, neonates, and young infants (> 4.5 months old), physiological conditions associated with different developmental stages and tissue turnover rather than diet govern collagen isotope variation. Ossicles predominantly archive mid prenatal physiology; deciduous dentin emphasizes late gestation (±immediate perinatal); long bone/rib integrates and dampens signals over a broader interval. This study recommends tissue‐aware sampling and reporting when inferring maternal diet, fetal physiology, and early‐life stress from collagen.