Extended Data Fig. 10: Permanent second molar of a modern Pongo specimen from the Perth Zoo.

The orangutan Hsing Hsing was born in captivity in 1975 in the Singapore Zoo, and was raised by its parents (although additional human feeding cannot definitively be excluded). The orangutan joined the Perth Zoo as an immature individual in 1983. There appears to be no Ba/Ca banding pattern that would indicate cyclical milk consumption during crown completion. The diet of this orangutan would have been substantially different to that of orangutans living in the wild, with limited seasonal influence and no periods of food scarcity. It is expected that the orangutan and its parents would have had abundant and guaranteed access to food, which would probably have led it to being prematurely weaned (compared to wild Pongo). On this basis, it is unlikely that this orangutan would have had recurrent breastfeeding cycles, and therefore the absence of barium banding in this specimen is expected. The discrete banding lines observed in the Sr/Ca and the two Ba/Ca ratios are probably stress-related accentuated lines. No clear banding was observed in the enamel of this specimen.