Fig. S1.

Plot of Δ¹⁷O vs. δ¹⁸O for sources (A) and sinks, BW, and bioapatite (B) for a scenario with 375 ppm CO₂. The mass balance was calculated for M_b = 5 kg and model δ¹⁸O_DW = –10.5 ‰. The ellipses outline the 1σ SD that was computed calculated by Monte Carlo simulation (n = 100). The uncertainties of the individual input parameters were taken from Pack et al. (50). The composition of fossil tooth enamel [sample E. osbornianus (Wa-2, locality SC-2), red star] is shown for comparison. (B and C) The same scenario as in A with an atmospheric CO₂ mixing ratio of 4,000 ppm. The model bioapatite (D, black diamonds) has much lower Δ¹⁷O than the analyzed bioapatite (red star).