Radiocarbon Dating of Eggshell Samples

Eggshell samples for radiocarbon dating (Supplementary Note 3 and Supplementary Data 3) were mechanically cleaned then reduced by 50% with the stoichiometric addition of 2N HCl in vacuo. Cleaned fragments were converted to graphite at the INSTAAR Laboratory for AMS Radiocarbon Preparation and Research (NSRL) before measurement by Accelerator Mass Spectrometry at the Keck Carbon Cycle AMS Laboratory at the UC Irvine (KCCAMS). Conventional radiocarbon ages have been calibrated using CALIB v.7.1 and SHcal13^{56 (link)–58} . Sample AD1739 was found in an archaeological deposit by KD; eggshell from the same context were radiocarbon dated as above.
The ratio of two enantiomers (A/I), the protein amino acid L-isoleucine and the non-protein diastereomer d-alloisoleucine, was measured in eggshell by ion-exchange high-pressure liquid chromatography (Supplementary Note 4); A/I reflects time and the integrated thermal history experienced by the sample. Quality control is monitored with a laboratory standard, ILC-G^{59 (link)}; 383A/I analyses of the ILC-G standard in the lab average 0.457 ± 0.012.