Study Of The Microtine Fossils From Luonan Zhangping,Shaanxi Province, China

The fossils of three species: Microtus oeconomus, Caryomys eva and C. Inez from Luonan Zhangping, shaanxi province are studied in this paper. All of the specimens are remained hi five caves on north side by Luohe River, Qinling Mountains, which are located at a same site but different altitude.It could be evident that the age of cave fauna is the mid-late Pleistocene, according to the three fossil species comparing with those of other fossil faunas related sites and according to the river terraces analysis near by Luohe River. Further, based on the survey and calculation the height of the caves above the Luohe River, we can divide the five caves into five stages as following (from upper to lower): 430Ka盉P, 262Ka盉P, 162Ka盉P, 100Ka盉Pand57Ka盉P.A central evolutionary trend of the Microtine is the gradual development of rootless, very high-crowned cheek teeth that grow throughout life and are well adapted to a highly abrasive diet Most fossil specimens are cheek teeth of voles. The shapes of the fossil microtine molars show a tendency from simply to complex as time goes on. Near the studied area, the fossil microtine show a sequence from the Early Pleistocene to the mid-late Pleistocene:Allophaiomys(Qi)桺redromys(Q\)桵icrotus(Q2-i)-On their molars, the 5th dentine isthmus Is5 show a closed trend from broad to narrow and made the salient angle tend to gradual increase. In the area, the 6th dentine isthmus Is6 of the Microtus show a trend from broad to narrow gradually.The highlight features of distribution of fossil and living three species microtine in the area are showed as followings: (1) the Microtus oeconomus which keeps moist and cold was most in the 3rd cave, but absent in recent; (2) meanwhile the Caryomys ienz which prefers dry and warm was absent in 3rd cave, but live in recent; (3) the Caryomys eva which prefers moist and cool was a little in 3rd cave and live in near sites recent.Maybe the environmental and climate change of the studied site and nearly area showed by distributions of the three fossil and living species microtine above is just as following:430Ka盉P, warm and moist: 262Ka盉P, cool and moist; 162Ka盉P, cold and moist; 57Ka盉P, cool and moist; Recent, warm and dry.