Carbon and nitrogen stable isotope analyses of mammal bone fossils from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River, China

Based on AMS C-14 dating data, carbon and nitrogen isotope analyses were conducted on mammal bone collagen of deer, cattle and pigs from the Zhongba site in the Three Gorges Reservoir region of the Yangtze River. These analyses were conducted to reconstruct palaeodiets of mammals, palaeoecology, palaeoenviroment and previous human activities in the study area. Results show that the collagen loss of bone did not change the in vivo isotopic composition of carbon and nitrogen stable isotopes, and most of the bone fossils were well preserved. The bone collagen of samples from deer had a mean delta C-13 of -23.1aEuro degrees and a mean delta N-15 of 4.7aEuro degrees, suggesting that deer subsisted in a closed habitat and fed on branches and leaves. The bone collagen of cattle had a mean delta C-13 of -19.6aEuro degrees and a mean delta N-15 of 5.2aEuro degrees, which indicates that cattle subsisted in an open habitat and fed on grasses and stems. The delta C-13 values show that both deer and cattle fed on C-3 plants and lived in the same ecosystem, but the t-test results show that deer delta C-13 and delta N-15 values were both more negative than those of cattle, indicating that they inhabited different niches. The delta C-13 and delta N-15 values of cattle partially overlapped those of deer, suggesting some competition in diets between them. The t-tests show that the delta C-13 and delta N-15 values of pigs were more positive than those of cattle and deer, which signifies that pigs occupied a higher trophic level compared to cattle and deer. The wide range of pig delta C-13 values demonstrates that pig trading had been taking place from early Neolithic Age to late Bronze Age. There were no significant differences in deer delta C-13 and delta N-15 values among different archaeological periods, making it clear that climatic, ecological and environmental conditions were kept relatively stable from 2200 to 4200 a BP. This stability may have been responsible for the extensive and complete cultural layers at the Zhongba site. The minimum number of samples required to estimate the mean delta C-13 values of deer, pigs and cattle are 8, 73 and 16, respectively, and for mean delta N-15 values of deer, pigs and cattle, the minimum numbers are 4, 5 and 6, respectively.