Stable isotopic evidence for diets and niche differentiation of Early Pleistocene panda and associated mammals from Yanliang Cave, South China

To better constrain the timing of panda's dietary shift from omnivorous to bamboo-exclusive herbivores, this study analyzed stable isotopes of carbon and oxygen in tooth enamel samples from two pygmy pandas from Yanliang Cave (early Pleistocene), three baconi pandas from Gongjishan Cave (late middle Pleistocene to early late Pleistocene), and five giant pandas from Baxian Cave (late Pleistocene) in the Chongzuo Ecological Park of Guangxi Province in South China. In addition, the carbon and oxygen isotope compositions of enamel samples from other mammals associated with the pygmy panda at Yanliang Cave were also analyzed. The results show that the pygmy panda, Ailuropod microta, had the lowest enamel-delta13C values compared to other coexisting mammals at -19‰, suggesting that the pygmy panda had a pure C3 diet composed of plants growing in the understory of a closed-canopy forest. A pure C3 diet for the pygmy panda, if confirmed by more data, would be consistent with an already established dietary niche of bamboo (a C3 plant). Reconstructed delta13C values of diets for the Yanliang fauna range from -25.6 to -32.1‰, indicating that these early Pleistocene mammals ate predominantly C3 vegetation and lived in an environment dominated by C3 plants. This suggests that the area was comprised of wooded habitats ranging from closed canopy forests to woodlands. Significant intra-tooth delta13C variations observed in some grazing animals suggest that a small amount of C4 grasses may be present in patches of open areas in a predominantly forested landscape. The reconstructed delta18O values of meteoric water in the area during the early Pleistocene fall within the range of -7.6 to -7.8‰; lower than the present-day mean annual precipitation delta18O values in the region, suggesting a wetter climate or stronger monsoon season in the early Pleistocene than today. The baconi panda (Ailuropod baconi) and giant panda (Ailuropod melanoleuca), had less depleted delta13C values with an average of -16.7‰ and -17.2‰, respectively, compared to the early Pleistocene panda. Assuming they also consumed bamboo exclusively, this would suggest an ecologic shift to a more open woodland environment towards the end of the Pleistocene.