Aminoisoscapes and palaeodiet reconstruction: New perspectives on millet-based diets in China using amino acid δ13C values

Abstract Foxtail millet (Setaria italica) and common millet (Panicum miliaceum) were important staple crops for the inhabitants of northern China since the Neolithic. The near exclusive consumption of these millets results in extremely elevated bulk collagen δ13C values (~−7‰ to −5‰), which serve as natural isotopic tracers in palaeodiet studies. Here we report individual amino acid δ13C results (δ13CAA) for humans (n = 12) and animals (n = 9) that consumed varying amounts of millets at the Proto-Shang period (2000–1600 BC) site of Nancheng, China. Using established δ13CAA proxies (Δ13CGly-Phe, Δ13CVal-Phe, and plots of δ13CPhe vs. δ13CVal, δ13CLys vs. Δ13CGly-Phe, and δ13CLys vs. Δ13CVal-Phe) and machine learning assisted principal component analysis (MLA-PCA), we compared the Nancheng data to published known archaeological C3, C4, marine and freshwater protein consumers. Exclusive millet-consuming humans and animals from Nancheng displayed highly 13C-enriched amino acid results, which were distinct from C4 consumers of maize (Zea mays) in the Americas. Compared to δ13CAA dietary proxies, MLA-PCA provides improved separation for all of the different dietary categories reviewed. Further, this method was able to distinguish additional dietary details, such as identifying brackish species. Increased application of MLA-PCA in palaeodiet research utilizing δ13CAA measurements could create regional and global aminoisoscapes that can reveal unique dietary and environmental information that is otherwise hidden by bulk and existing δ13CAA proxy isotopic analyses.