Miocene squirrels from Linxia Basin, Gansu, China; paleoenvironmental and palaeoecological implications

This paper presents the Miocene squirrels of the Linxia Basin in Gansu Province, and a paleoenvironmental and palaeoecological analysis based on the remains collected recently by screen-washing nine localities of early to late Miocene age. The assemblages contain 12 sciurid species (nine genera, three subfamilies), including squirrels with different adaptations, predominantly ground squirrels and chipmunks. Our analysis suggests that Miocene squirrels in Linxia reflect a relatively dry climate and open shrub-steppe environment, and favorable dispersal across Eurasia. The Linxia Miocene squirrels show close taxonomic composition with contemporary faunas known from the Mongol-Xinjiang highland and adjacent regions, implying that northern China represents a single biotic province with uniform paleoenvironment. In addition, the Linxia squirrels are quite different from those found in Yunnan in southern China, which are dominantly tree and flying squirrels that suggest a humid forest biotope. The differences in distribution indicate that Miocene squirrel faunas of China showed distinct provinciality and latitudinal ecological variation. Already in the Miocene we see evidence for predecessors of the present-day Palearctic and Oriental zoogeographic provinces of North and South China.