Calcium isotope ecology of early Gigantopithecus blacki (∼2 Ma) in South China

Gigantopithecus blacki is the largest hominoid with massive jaws and thick tooth enamel in the world and lasts from the early Early Pleistocene to the middle Pleistocene in South China. Understanding its foraging ecology is vital to unlocking the mysteries of its survival, evolution, and extinction. Although many analytical methods have been applied to reveal its foraging ecology, there is still a lack of direct evidence on the trophic level of G. blacki. For the first time, we presented the Ca isotope data of Gigantopithecus fauna at the locality of Liucheng Gigantopithecus Cave (∼2 Ma), Guangxi, China during the early Early Pleistocene. The isotopic pattern from herbivores to carnivores is following the general trophic rule, i.e., the step decrease of ^{δ 44 / 42}Ca values alongside the food chain. However, the cervids and Stegodon have extremely low ^{δ 44 / 42}Ca values that are close to carnivores (hyenas) while G. blacki and Ailuropoda have the highest ^{δ 44 / 42}Ca values among animals. When compiling the isotopic (δ¹³C, δ¹⁸O, ^{δ 44 / 42}Ca) data together, we distinguish the animal niches well. Considering the dietary and physiological factors to influence ^{δ 44 / 42}Ca values in diets, we suggest that cervids and Stegodon could have consumed lots of grasses and/or bones as an additional mineral supplement and that G. blacki and giant panda might have fed on C₃ plant leaves and/or minerals from soils or rocks. The comparison of ^{δ 44 / 42}Ca values among G. blacki, modern primates, and hominins indicates the significantly highest ^{δ 44 / 42}Ca values in G.blacki in Asia and Paranthropus boisei in Africa. Even though both animals have distinctive δ¹³C and δ¹⁸O values, they have quite close ^{δ 44 / 42}Ca values, suggesting a possible shared similar mechanism of Ca fractionation. Finally, the implications of ^{δ 44 / 42}Ca values to reveal animal diets and physiology on species-specific scales were discussed. We hypothesize that foraging on mineral licks from soils or rocks could have been one of the main driving factors to account for the high ^{δ 44 / 42}Ca values in the enamel of G.blacki, P. boisei, and giant panda, which possibly meets physiological demands to adapt to chew hard foodstuffs. Our study provides novel insights into the uniqueness of G.blacki's foraging ecology and displays the complexity of Ca isotope values to decipher animal diets and physiology.