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近百年来,在内蒙古中部地区发现了丰富的新近纪哺乳动物化石,命名和描述了10余个哺乳动物群,其时代跨越早中新世至早上新世.它们已经成为建立中国北方新近纪哺乳动物生物年代地层框架的重要依据.早在1959年中苏古生物联合考察过程中就已经发现土城子地区有丰富的哺乳动物化石,但这些化石以大-中型哺乳动物为主,缺乏小哺乳动物.土城子动物群的构成和其在中国北方新近纪哺乳动物年代地层框架中的位置长期以来不是特别明确.报道了在土城子新发现的6种小哺乳动物化石.根据Lophocricetus grabaui-Sinocricetus zdanskyi-Prosiphneus licenti-Hansdebruijnia pusilla-Moschus grandaevus的组合特点,认为土城子动物群的年代应该可以很好地约束在晚中新世(或者保德期)的晚期.土城子动物群明显比内蒙古的宝格达乌拉动物群要进步一些,与二登图动物群非常相似,时代上晚于前者,略早于后者.依据动物群整体面貌,推测在晚中新世晚期土城子地区存在森林和草原混合的环境.“,”Neogene strata rich in fossil mammals are well exposed in central Nei Mongol,China.Over a dozen mammalian faunas in chronological succession from Early Miocene to Early Pliocene were discerned in this region,and they built a fundamental part of the Neogene land mammal biochronological system in northern China.Tuchengzi was first recognized for producing abundant mammalian fossils during the Sino-Soviet Paleontological Expedition(SSPE)initiated in 1959.However,all unearthed fossils from the SSPE were either large-or middle-sized mammals,and small mammal fossils in the Tuchengzi Fauna were deficient for a long time.The composition and biochronological position of the Tuchengzi Fauna in the Neogene mammalian biochronological system in northern China was not particularly clear.The new fossils here reported are represented by 6 taxa of small mammals.Based on the co-occurrence of Lophocricetus grabaui,Sinocricetus zdanskyi,Prosiphneus licenti,Hansdebruijnia pusilla,and Moschus grandaevus,the age of the Tuchengzi Fauna is constrained to late Late Miocene or Baodean Chinese Land Mammal Age,slighter younger than the Baogeda Ula Fauna and older than the Ertemte Fauna.Judging from the fossil composition,the Tuchengzi Fauna possibly inhabited a forest-steppe mixed habitat during the late Late Miocene.