Isotopic Values of Prenatal Development: δ¹³C and δ¹⁵N Variation in Early-Formed Human Tissues

Carbon (δ¹³C) and nitrogen (δ¹⁵N) 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.

Collagen δ¹³C and δ¹⁵N 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 reveal a consistent δ¹⁵N trajectory: values generally increase from ossicles to teeth and decrease from teeth to long bone/rib. Tooth-long bone/rib δ¹⁵N offsets are significant across the sample and within each age group. δ¹³C 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 δ¹³C 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.

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.