Magnetochronology of Mid-Miocene mammalian fauna in the Lanzhou Basin, northeastern Tibetan Plateau: Implications for Asian mammal migration

The Quantougou (QTG) Fauna in central Lanzhou Basin is an important late Mid-Miocene fauna on the northeastern Tibetan Plateau margin, but its numerical age remains a matter of debate. Here, we present a new magnetostratigraphic record for a fluvio-lacustrine section to further constrain the age of the QTG Fauna. Results suggest that the studied section spans from polarity chrons C5Cn.2n to C5n.2n or C5An.1n, with ages of ca. 16.5 Ma to 10 Ma or 16.5 Ma to 12 Ma. The QTG Fauna is located at the top of polarity chron C5r.3r or C5Ar.2r, which corresponds to an age of 11.7 Ma or 12.8 Ma for the fauna. Accordingly, the associated Myocricetodontinae (a subfamily of Gerbillidae, Rodentia) is suggested to have appeared in the Lanzhou Basin at 11.7 Ma or 12.8 Ma, which is the oldest Myocricetodontinae in East Asia but is still much younger than the ~20 Ma appearance of this subfamily in West and South Asia. Our age data support the interpretation that East Asian Myocricetodontinae originated from South Asia. The QTG fauna further suggest a dry and open grassland environment, which is consistent with global cooling after the Mid-Miocene Climatic Optimum.