华北晚中新世羚羊的食性与古环境——稳定碳同位素的证据

通过分析华北晚中新世保德期三个经典地点的羚羊牙齿釉质之稳定碳同位素,结合相同地点的单纯食叶者(鹿科)与食草者(三趾马)的数据,推断其食性取向。结果显示这些晚中新世生态系统中C_3植物占据主导地位,但也含有一小部分的C_4植物(可能小于30%)。高冠羚羊(Gazella dorcadoides类型)取食约20%的C_4植物,而中冠羚羊(G．paotehensis类型)与低冠羚羊(G．gaudryi类型)为纯C_3植物消费者。鹿科动物单纯取食C_3植物,而三趾马与G．dorcadoides类型的羚羊取食C_4植物的比例在统计上难以区分。碳同位素数据与G．gaud- ryi类型的食叶性以及G．dorcadoides类型以草食为主的观点相一致。参照这些类群的地理分布,当前的数据支持晚中新世黄土高原东南部处于相对于西北部更为封闭环境的观点。这种环境梯度的分布方向与模式可能是该地区东亚季风体系的早期信号。

PALEODIETS AND PALEOENVIRONMENTS OF LATE MIOCENE GAZELLES FROM NORTH CHINA: EVIDENCE FROM STABLE CARBON ISOTOPES

We use carbon isotopes in fossil tooth enamel to infer dietary preferences in Baodean ( Late Miocene) gazelles from three classical localities in North China, along with putative browsers (Cervidae) and grazers (Hipparion) from the same localities. The results suggest that these Late Miocene ecosystems were dominated by C3 vegetation, but contained a small fraction of C4 vegetation ( probably less than ～ 30% ). We find that the higher-crowned gazelles (Gazella dorcadoides-type) consumed up to ～20% C4 plants, whereas G. Paotehensis-type gazelles (intermediate crown-height forms) and G. Gaudryi-type gazelles (low-crowned forms) had essentially pure C3 diets. Cervidae consumed pure C3 vegetation, while Hipparion consumed some C4 vegetation and is statistically indistinguishable from G. Dorcadoides-type gazelles. The carbon isotope data are consistent with a primarily browsing diet in G. Gaudryi-type gazelles, and a larger fraction of graze in the diet of G. Dorcadoides-type gazelles. Taken with the distributions of these taxa, the data support the established concept of relatively closed habitats in the southeast CLP (Chinese Loess Plateau) compared to the northwest CLP during the Late Miocene. The direction and pattern of this environmental gradient may be an early signature of the East Asian Monsoon system in this region.