Large-sized fossil hamsters from the late Middle Pleistocene Locality 2 of Shanyangzhai, China, and discussion on the validity of and (Rodentia: Cricetidae).

A detailed morphological description and comparative study were conducted on numerous large-sized hamster remains collected from the late Middle Pleistocene Locality 2 of Shanyangzhai (Syz 2), Hebei Province, China. The comparisons reveal that these fossils are highly similar to the extant in size and morphology, including the small degree of alternating between the main opposite cusps on M1-3, the presence of axioloph on M3, and mesolophids on m1-2 that are present but seldom reach the lingual margin of the teeth, among other features. However, minor differences between the two still exist. Consequently, all these fossils are designated as a chronosubspecies of the extant species, comb. nov. The skull and molar morphologies of and were meticulously compared to resolve the long-standing debate regarding the validity of Zdansky, 1928 and Zdansky, 1928. The findings indicate that the differences between the two are slight; as a result, can only be considered a chronosubspecies of , ., comb. nov., and should be recognized as a junior synonym of . We tentatively propose that, among the seven species once referred to , , , , and should be reassigned to , while should be transferred to , and to . Excluding . from the Late Pliocene Youhe fauna, there are no reliable fossils in China earlier than the Middle Pleistocene. Based on the current evidence, may have originated from during the Early Pliocene in Europe and subsequently spread to Asia. is its sole surviving representative, which now exclusively inhabits East Asia.