The evidence of fossil carbon isotopes of the climatic event at the beginning of Quaternary

Tooth enamel of mammalian fossils can efficiently preserve the original car bon isotopic composition when they lived. The ungulate fossils, especially equids in the early Early Pleistocene Bajiazui fauna from Qingyang, Gansu a re studied. According to the enriched relation of carbon isotopes between m ammalian tooth enamel and grass diets, the fractions of C-3 and C-4 plants in this region at that time are reconstructed, which indicates that C-3 gra ss occupied a dominant position. Because C-3 grass adapts itself to cold an d damp climates, our analytic results show that the time of the Bajiazui fa una was in a critical state between a glacial stage beginning and a summer monsoon retreat, and it was a refection to the turning cold event of the gl obal climate at the beginning of the Quaternary.