Fig. 2. Dentine barium patterns across the first molars of three immature wild orangutans.

Calcium-normalized barium concentrations quantified from the beginning of first molar calcification (dentine horn tip) until the end of crown formation or the end of available root dentine in three immature wild orangutans. Ages are presented on a nonlinear scale that relates to the changing rate of extension during molar crown formation. Red brackets denote an increasing pattern of barium incorporation due to milk consumption during the first 1 to 1.5 years of life. (A) Bornean individual (ZSM 1981/48), (B) Sumatran individual (ZSM 1981/246), and (C) Sumatran individual (ZMB 83508). Although barium concentrations were markedly different between animals, values were consistent among teeth from the same individual (see Figs. 3 and 4 and fig. S1). Interindividual variation is consistent with variation in barium breast milk from six modern human subjects (39).