The micromammal fossils collected from the Shangzhuang Formation of the Linxia Basin, Gansu, are described here. The assemblage consists of 16 species of 13 genera belonging to 7 families, including one new species and one taxon previously unknown from China. Among them 5 genera are Oligocene holdovers and 11 genera/species are known to make their first appearances in Early Miocene, indicating an Early Miocene age for the Gucheng Fauna. The absence of Oligocene survivors such as Tataromys, Yindirtemys, Eucricetodon and Tachyoryctoides, which usually occur in the Xiejian age of Early Miocene, and the presence of newcomers Protalactaga, Megacricetodon and Gobicricetodon, that made their first appearance only in the Shanwangian age of late Early Miocene, suggest that the Gucheng Fauna is of a later age of Early Miocene. The new species, Sinolagomys guchengensis, showing more derived morphology than in S. ulunguensis, seems to support an assessment of the fauna in Shanwangian age. Thus, the Gucheng Fauna may belong to late Early Miocene Shanwangian, partially equivalent to MN 3/4 of the European land mammal zonation. Ecological analysis of the fauna indicates that the palaeoecological condition of the Gucheng area might still be a predominantly arid shrub-steppe in late Early Miocene.
