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

Abstract （829）

HTML （10）

PDF（pc）（2568KB）（206）

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. 4 Scatter diagrams showing the length and width of the first two molars of Nannocricetus primitivus from Yihachi, Gansu and some other localities in northern China
Measurements of specimens from Lantian, Shengou and Baogeda Ula are cited from Zhang et al., 2008, Qiu and Li, 2008, 2016

Nannocricetus primitivus is a relatively primitive species of the genus. In addition to the Early Miocene Lantian in Shaanxi, the type locality of the species, it is also recorded in Shengou, Early Miocene in Qinghai, and in several Late Miocene localities (Balunhalagen, Shala, Huitenghe, Baogeda Ula and Bilutu) in central Nei Mongol. Of these localities, Yihachi produces the richest materials. Individuals in all the populations show homogeneous tooth characters, and most fall within the range exhibited by the Yihachi populations regarding size (Fig. 4). Major differences seem to be the root numbers in the M1-2 and the development of anterolophule(id) of M1 or m1 in these populations, which may be interpreted as an early stage of evolution for this species. Nannocricetus primitivus (frequently observed with a 4-rooted M1-2) from the upper lens of the Yihachi section must be more derived; there are mostly 3 roots for the lower lens. The genus Nannocricetus appears to show a gradual increase in size, crown height, and root number. In addition, the anterocone(id) gradually separates while the anterolophule(id) strengthens, and the mesoloph(id) gradually reduces or disappears over the course of time.