Abstract: Since the 1983-84 excavations, two semicircular structures identified by hundreds of animal bones were recovered at the Yanjiagang site, Harbin, Heilongjiang Province. Based on the contents, excavators interpreted this site to be an Upper Paleolithic camp site. The nature of this semicircular structure has been debated, leading to the publication of several papers. According to previous studies, there are two points of view on the origin of such structures. One view, proposed by the former excavators, claims that these structures were artificial remains constructed intentionally by ancient hunter-gatherers; the other, argued by other scholars, suggests the nature of these structures to be fluvial deposits formed through natural agent. This paper presents an alternate hypothesis on the formation of these two structures.
The paper starts from the ethnoarchaeological comparsion of dwelling sites of hunter- gatherers. Referring to the location, characteristics and the composition of animal bones in these dwelling sites, the authors believe that it is unreasonable to recognize the structures at Yanjiagang as dwelling huts. In comparison with other Upper Paleolithic dwelling sites, mostly in Europe, the authors found a few shared characteristics such as the composition of animal bones, hearth, post holes, and lithic materials. We discuss the possibility that these structures were used as hunting shelters, but a comparison with ethnoarchaeological data shows that other agents can be used to explain the accumulation of animal bones, for example, (i.e., carnivores such as wolves). Note that nearly 12% of the marks on animal bones came from carnivores.
This paper argues that a natural mechanism, i.e., a freeze-thaw process could have been a potential mover of artifacts, animal bones, and other sediments, which led to the formation of the semi-circular structure. This process is widely found in environments where the ground freezes annually to varied depths. The rate of earth movement is highly variable due in part to in materials on the ground. A semi-circular structure could come into being with similar conditions. At present, we hypothesize, subject to future testing, that the semi-circular structures of Yanjiagang most likely resulted from the circulation of freeze-thaw action and water transportation.

Key words: Yanjiagang; Semicircular structure; Dwelling sites; Ethnoarchaeology; Freeze- thaw action