Hualongdong (HLD) site in Dongzhi County, Anhui Province is another important locality for early hominin skull fossils following notable sites such as Zhoukoudian in Beijing, Lantian in Shaanxi, Hexian in Anhui and Tangshan in Nanjing. The geological age of the site is approximately 300 ka. Since its discovery in 2004, multiple excavations have been conducted at HLD site, yielding abundant hominin and associated vertebrate fossils. This study focuses on the taxonomic identification, faunal analysis of non-volant small mammal fossils associated with hominin fossils from the 2015-2017 excavation, and paleoenvironmental reconstruction. A total of 5,645 non-volant micromammal fossil specimens have been discovered, primarily consisting of isolated teeth. These fossils represent 3 orders, 11 families, 38 genera, and 49 species (including two species indeterminata). In terms of both the number of species and the number of identified specimens, Rodentia is dominant at the ordinal level; Muridae is the most diverse at the familial level; and Apodemus is the most abundant at the generic level. The extinction proportion of HLD site is low (4.26%), which is obviously different from the Early Pleistocene and the early Middle Pleistocene non-volant small mammal assemblages with abundant Tertiary relict species, and the Late Pleistocene animal assemblages with almost complete disappearance of extinct species, but more similar to the late Middle Pleistocene small non-volant mammal assemblage in southern China. In terms of faunal composition, the non-volant micromammalian assemblage of the HLD site shows the higher similarity to that of Yumidong of Chongqing, Xinglogndong of Chongqing, Yanhuidong of Guizhou, and Baotansi of Chongqing. The comparison with the present small mammal assemblages shows that remarkable species alternations have taken place in this region, with the decline in species quantity of Soricinae, flying sciurids and Apodemus, the emergence of temperate species Myospalax and the disappearance of subtropical and tropical species since the late Middle Pleistocene to the present.

The 45 extant species at the HLD site collectively reflect a forest-dominated habitat; however, the top eight dominant species, as determined by minimum number of individuals (MNI), indicate a mixed forest-grassland environment. Based on the MNI, we analyzed the habitat preferences of these dominant species. Among them, Pteromys volans and Lasiopodomys brandtii are primarily distributed in temperate regions; Eothenomys melanogaster is usually inhabited subtropical and tropical shrublands; species of Apodemus and Niviventer andersoni are mainly found in temperate and subtropical areas; while Mus musculus is widely distributed from tropical to temperate zones. These species typically inhabit various forest types and meadow environments at forest edges. In light of the small mammal assemblage, we infer that the HLD site in Dongzhi, Anhui, during the late Middle Pleistocene, featured a mixed environment of forests and meadows. The mean annual temperature (MAT) and mean annual precipitation (MAP) reconstructed using the Random Forest algorithm for the late Middle Pleistocene HLD site were 12.57°C and 909.81 mm (based on the eight MNI dominant species) and 13.38°C and 1014.70 mm (based on all 45 extant species), respectively. These values are lower than the meteorological data from present-day Dongzhi (16.1°C and 1628.3 mm), indicating that the climate at that time was somewhat cooler and drier.