Abstract:

As a crucial Middle Pleistocene hominin activity site, Hualongdong (HLD) provides pivotal evidence for understanding ancient human evolution and environmental adaptation in East Asia. The site's hominin fossils and stone tools were unearthed from breccia and brownish-red clay deposits. To reconstruct the paleovegetation and better understand the paleoenvironmental context of the Hualongdong hominins, this study conducted pollen analysis on 20 sediment samples collected from these strata in the 2016 excavation area. A total of 41 pollen taxa were identified across the samples. From the breccia deposits (7 samples), 94 pollen grains were recovered, whereas 1,148 grains were counted in the 13 samples from the HLD2016 section. Uranium-series dating of stalagmites and animal teeth fossils indicates that the breccia deposits formed between 331 and 275 ka BP. Although the HLD2016 section lacks direct dating, published chronostudies suggest that the brownish-red clay was deposited during the late Middle Pleistocene, approximately 0.4~0.1 Ma. Notably, the pollen assemblages from the lower portion of the HLD2016 section (below 150 cm) closely resemble those of the breccia deposits. This similarity suggests that the sedimentary layer between 240 and 150 cm may correspond temporally to the breccia deposits.

In the breccia samples and the HLD2016 sediments below 150 cm, arboreal pollen dominates (67.7%), followed by herbaceous (31.9%) and shrub pollen (0.4%). The assemblage reflects a deciduous broad-leaved forest dominated by Ulmus and Quercus, with an understory and surrounding grasslands composed of Poaceae, Chenopodiaceae, and Artemisia. This vegetation structure is distinct from the region's current subtropical environment but similar to the warm-temperate deciduous broad-leaved forests of southern North China suggests that the climate during the Hualongdong hominin occupation was cooler and drier than today. The landscape likely consisted of a forest and grassland mosaic, offering diverse ecological resources. Comparative analysis reveals that Hualongdong's paleoenvironment shares similarities with that of the Nanjing site but exhibits denser vegetation cover than Zhoukoudian and Dali, along with intermediate openness compared to Miaohoushan and Xujiayao. These environmental features may reflect the ecological adaptation strategies of Middle Pleistocene hominins in East Asia, particularly their utilization of mixed forest-grassland ecotones. The mosaic of deciduous broad-leaved forests and open grasslands would have provided both shelter and hunting opportunities, supporting a dynamic subsistence strategy.

Key words: Dongzhi, Middle Pleistocene, pollen analysis, paleoenvironment, glacial-interglacial