An updated age for the Xujiayao hominin from the Nihewan Basin, North China: implications for Middle Pleistocene human evolution in East Asia

With an inventory of >60 early Paleolithic sites, >100,000 in situ stone tools, and tons of mammal fossils, the Nihewan Basin in North China is one of the most important Paleolithic areas in East Asia. The Xujiayao site in the northwestern margin of Nihewan Basin is one of the most important Paleolithic sites worldwide. Twenty archaic Homo fossils have been excavated along with more than 30,000 lithic artifacts and 5000 mammalian fossil specimens. Dating of the Xujiayao hominin has been pursued since its excavation in the 1970s, but its age has remained controversial because of limitations of the previous dating techniques that have been applied to available materials. Here, we report new ages for the Xujiayao hominin based on combined electron spin resonance (ESR) dating of quartz in the sediments and high-resolution magnetostratigraphy of the fluvio-lacustrine sequence. The magnetostratigraphy suggests that the upper Matuyama and Brunhes polarity chrons are recorded at Xujiayao. The ESR dating results indicate a pooled average age of 260, 370 ka for the Homo-bearing layer, which is consistent with its position within the middle Brunhes normal polarity chron indicated by magnetostratigraphy. This age estimate makes the Xujiayao hominin among the oldest mid-Pleistocene hominins with derived Neanderthal traits in East Asia. Our updated age and the Neanderthal-like traits of the Xujiayao Homo fossils, particularly the Denisovan-like molar teeth, make it possible that the Xujiayao hominin could represent an early Denisovan, a sister group of Neanderthals. If this Homo species affiliation is documented by DNA study, it will imply that Neanderthals expanded to East Asia as early as 370 ka, just 60 ka after the origin of Neanderthals in West Europe at 430 ka, and then they further involved into typical Denisovans under local climatic and demographic pressure.