Dipodidae (Rodentia, Mammalia) from the Miocene of Damiao, Nei Mongol, China

The Damiao deposit in Nei Mongol, China is a crucial locality for Neogene stratigraphy and faunal turnover in Central Asia. In this study, we described thirteen dipodid species, including two new species, Sinozapus damiaoensis sp. nov. and Lophocricetus parvus sp. nov.. Sinozapus damiaoensis sp. nov. is distinguished by the metaloph connecting to the central hypocone on M1-2, the absence of the anterior arm of the protoconid, and the posterior arm of the protoconid merging with the metaconid on m2. Lophocricetus parvus sp. nov. presents a suit of transitional morphological traits between Heterosminthus and Lophocricetus. It is similar to Heterosminthus by its small size, the presence of the mesocone and mesoloph on M1-2, double anteroloph on M2, remnant of the pseudomesolophid, and the posterior crest of the protoconid on m1. Meanwhile, it possesses the characteristics of Lophocricetus , including the protostyle on M1 and the connection of hypoconid-entoconid on m1. These two new species represent the earliest records of their respective genera. These new fossil records further expand the diversity of Neogene dipodids. Additionally, biostratigraphic comparisons with adjacent regions have refined the Neogene stratigraphic framework of the central Nei Mongol. Faunal transitions can be observed from small, low-crowned primitive taxa adapted to the relatively humid environments of the Early Miocene to an increasing ecological diversification by the late Middle Miocene. The emergence of desert-adapted jerboa taxa indicates regional aridification and grassland expansion. However, relict sicistines and zapodines suggest localized persistence of humid refugia during broader drying, which is consistent with previous studies.