中文摘要：

洞沟剖面6个层位（第2、4、7、11、16和19层）的小哺乳动物化石揭示剖面第10与第11层间是晚上新世／早更新世界限。界限之上Ochotona youngi、Borsodia chinensis、Allophaiomys deucalion和Yangia trassaerti等首次出现；界限之下Yangia omegodon和Hypolagus schreuderi首次出现以及Paenelimnoecus、Nannocricetus mongolicus、Sinocricetus progressus、Mesosiphneus paratingi、Micromys tedfordi和Dipus fraudator最后绝灭。根据小哺乳动物组成及其属种转换事件判断，2．58Ma左右往后气候环境显著向干冷方向转变。

英文摘要：

Both the Pliocene Laowogou section and the Pleistocene Danangou section in the Nihewan Basin have recently been restudied by Zhang et al. in 2003 and Cai et al. in 2004. However, small mammals collected near the Plio-Pleistocene boundary in these two sections are rare. To make up this deficiency, the Donggou section, about 500 m northeast of the Qianjiashawa village, described by Yang et al. in 1996 （ Fig. 1 ） was selected in 2005 for looking for fossils. By the water-screening method, many small mammals were collected from the layers 2, 4, 7, 11, 16 and 19 respectively. The distributions of small mammalian species in this section are shown in Table 2. The species from the three lower layers can be supplemental from each other with the three layers of the Xiaoshuigou section, about 800 m south of the Donggou section, described by Duet al. in 1988 （ Table 1 ） stratigraphically and biologically.