Cricetids (Rodentia, Mammalia) from the Late Miocene Yihachi locality of Gansu, China

QIU Zhu-Ding, Lawrence J. FLYNN, WANG Ban-Yue, LI Lu

Vertebrata Palasiatica 2026, 64 (1): 1-25. DOI: 10.19615/j.cnki.2096-9899.251117

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Our purpose in this paper is to describe the hamster-like rodents (Cricetidae) from a Late Miocene age site in Linxia Basin, Gansu Province, and discuss their significance for the changing ecology of central Asia. The micromammal site known as Yihachi was introduced previously (Qiu et al., 2023; Qiu and Li, 2023), when its squirrels were discussed in some detail. We take this opportunity to describe the more abundant cricetids. There are four genera, common Nannocricetus and Sinocricetus plus the less abundant living Mesocricetus. A few specimens represent the high-crowned and lophodont Rhinocerodon. The cricetids and other faunal elements indicate an early Late Miocene age, and the pattern of occurrence of the hamster species is consistent with a picture of a changing paleoenvironment due to increasing effects of the East Asia monsoon system. After the disappearance of older and archaic genera, Yihachi represents growing endemism in the Late Miocene of northern China due to increasing seasonal rain and the declining average temperature.

Fig. 10 shows the biostratigraphical ranges of various species of the cricetid genera present in the Yihachi Fauna. Nannocricetus shows relatively high diversity, with the first record of N. wuae in the early Late Miocene and the last occurrence of N. mongolicus and N. qiui in the Early Pliocene. N. primitivus from Yihachi displays primitive features, but it is slightly more derived than N. wuae and much more primitive than the Early Pliocene N. qiui in morphology. The new species of Sinocricetus from Yihachi also exhibits distinctly more primitive characters than either in the Baodean S. zanskyi, or the Gaozhuangian S. progressus and S. major, in size, in crown height, anterocone(id) separation, development of mesoloph(id), and in the root numbers of M1 and M2. Mesocricetus fengi is the first record of the genus in the Late Miocene. It shows some similarities to the Early Pliocene M. primitivus from Rhodes and Aepyocricetus liuae from Xizang in morphology (de Bruijn et al., 1970; Li et al., 2018), but it is more like the former than the later, and it is thought to be a primitive species of Mesocricetus. The new species Rhinocerodon retains incomplete lophodonty, a small anterocone(id), strong protoloph I, distinct paracone-metacone connection on M1, and an absent buccal arm of hypoconid on m1, which can be interpreted as primitive for all known species from Kazakhstan and China. All four species of the Cricetidae from Yihachi suggest an early evolutionary stage for each genus, and likely an early Late Miocene age. Thus, the cricetid association may further validate the previous age assessment as dating to the early Late Miocene as proposed by Qiu and others in 2023, or Bahean in the LMA/S system (Qiu et al., 2013). Sinocricetus primus, Mesocricetus fengi, and Rhinocerodon linxiamys in this fauna represent the first appearance of each genus in the Late Miocene.