Bi-variate scatter plot of the δ¹³C and δ¹⁵N values of animal and human bone collagen from Xipo.

The predictive ranges for C₃, mixed and C₄ dietary groups are determined by the mean values of C₃ plants [19, 21] and C₄ millets [67, 68], plus ¹³C enrichment of 5 ‰ between diet protein and collagen [69, 70]. Human isotopic data are from the Institute of Archaeology CASS and Henan Provincial Institute of Cultural Heritage and Archaeology [47]. 95% prediction confidence ellipses are drawn for Sus, Bos, Cervus and humans; other species have too few data points. ‘PIG-1’ and ‘PIG-2’ were recovered from the bottom of the moat. ‘Kiln-1’ was recovered associated with the ceramic kiln. The modelled values for different consumer groups are symbolised by open diamonds and calculated as follows. The pure ‘millet consumer’ is based on published millet mean δ¹³C values + a stepwise diet-consumer collagen shift of +5 ‰, and mean δ¹⁵N value with an estimated trophic step of + 4 ‰. For ‘pig consumer’ we used the Xipo pig mean δ¹³C + 1 ‰ as the trophic step for δ¹³C, and mean δ¹⁵N + 4 ‰ as the trophic shift. For ‘natural C₃ feeder’, we used the mean δ¹³C and δ¹⁵N for wild herbivores and for any wild animal consumers we used the latter + 1 ‰ and + 4 ‰ for δ¹³C and δ¹⁵N respectively.