Abstract:

The Hualongdong (HLD) site (latitude 30°06′34.1"N, longitude 116°56′54.2"E, 40 m above sea level) is located in Dongzhi County, Anhui Province, China. It was discovered in 2005. The initial excavations at the HLD site in 2006 yielded a hominin frontal fragment and a lower second molar. Renewed excavations were carried out from 2014 to 2019 field seasons which resulted in the discovery of more than 30 human fossils, an abundance of lithic artifacts and fossil mammal fauna. Biostratigraphic study of faunal remains, as well as Uranium-Thorium dating of speleothems and animal teeth from the brecciated deposits indicated that early human occupied the site most probably took place in the late Middle Pleistocene, ca. 300 ka (270-330 ka). This paper presents the cave development and evolutionary history of the HLD site, and provides explanations of the hominin adapted behavior and the function of the site.

HLD cave is situated in the south slope of a small anticline named Meiyuan Hill. Constrained by the regional geological background, geomorphic features around HLD include lower mountains in the southeast, gentle hills and a lake plain in the northwest. The ancient HLD cave developed in the Upper Cambrian Formation, which consists of banded micritic limestone and dolomitic limestone, materials formed in a deep marine environment, and has been moderately karstified and mineralized over time. The initial formation of the ancient HLD cave likely commenced not later than the early Middle Pleistocene, as many broken speleothems were dated beyond the upper limits of the U-series dating. The original cave deposits were about 20 m higher above its current location, as indicated by the in situ flowstone and stalagmites exposed, which were formed inside the ancient HLD cave. Synsedimentary dismantlement, downward slippage, and bedrock weathering are indicated by the brecciated arrangement of the limestone rock blocks, cemented angular, subangular clasts and archaeological remains within the excavation area. Slipping and collapsing of the cave system proceeded from north to south, probably driven by the down-cutting of the valley and karst erosion.

Bone fragmentation is common and includes both diagenetic and green fractures probably produced by carnivore bone cracking and hominin hammerstone breaking. Additionally, carnivore (tooth pits, gnawing and scores marks) and human (cut marks) actions are documented over the bones. The stone tool assemblage is typical of Mode 1, i.e. the core-and-flake industries. Typologically, the HLD lithic assemblage is small (n=38) and is dominated by quartz (65.8%) and chert (21.1%), plus some lava (10.5%) and limestone (2.6%) artifacts. Most stone tools are complete flakes (60.5%) or debitage (31.6%), with only one specimen each of core, retouched and battered artifact categories. Quartz and lava show fluvial cortex and suggest sourcing from streams, whereas chert nodules derive from the nearby Sinian siliceous carbonate-clastic strata formation. A minimum of 44.4% of the quartz products were obtained through bipolar flaking, whereas all of the chert flakes were knapped with a freehand technique. The raw material quality of chert flakes is high, which may explain heavier reduction observed in their dorsal faces. Most chert flakes show use-wear, probably associated with carcass processing given the presence of cutmarks on some bones.

Although human presence at HLD site is attested by the recovery of their fossils and the small samples of cut-marked bones and stone tools, human activity seems to have been marginal at the site. Two possible scenarios can be deduced, either humans occasionally visited HLD site to briefly process animal remains attracted by carcasses abandoned by carnivores, or natural transport processes such as slope wash or gravity resulted in a fortuitous association between the carnivore-accumulated bone assemblage and lithics.

Key words: Hualongdong site, Cave system evolution, Human evolution, Middle Pleistocene, Anhui Province