Abstract:

Starting in 2014, ten years field work of excavations and deposit cleaning at the Hualongdong site, Dongzhi County, Anhui Province have resulted in more than fifty pieces of hominin fossils (including one well preserved skull), and stone tools and other evidence of hominin activities. Through fauna composition analysis and isotope dating, the hominin fossils were dated to about 300 ka. With these findings, the Hualongdong has been ranked as the most abundant hominin fossils and stone tool sites of Middle Pleistocene with Zhoukoudian. For the past ten years, a series of research with hominin fossils of cranium, facial bones, mandible, limb bones and teeth from Hualongdong have been conducted. Some new discoveries and understandings have been achieved from these studies. Our studies indicate the morphological traits of cranium, facial bones, mandible, limb bones and teeth from Hualongdong exhibit mosaics with combinations of East Asian Middle Pleistocene Homo erectus, Late Pleistocene hominin and modern human patterns. The cranium of Hualongdong has a suit of archaic features resembling those of East Asian Homo erectus, including low cranial vault, frontal keel, pronounced supraorbital torus, low position of maximum cranial breadth, slopping nasal floor and relatively small cranial capacity. Moreover, the cranium, facial bones, mandible and teeth show some derived features linking with Later Pleistocene hominins and modern humans. The modern human features in the Hualongdong hominin fossils include thin cranial wall, flat and gracile face, nearly vertical mandible symphysis, occurrence of initial mandibular trigon, and small and simple morphology teeth.

The hominin fossils discovered from the Hualongdong site were regarded as the one population living in the same time from 270~330 ka. During the studies of the hominin fossils, we noticed some variabilities in the expressions of some morphological features. The lower second molar and the frontal bone discovered in 2006 exhibit a suit of feature patterns that are usually found in East Asian Homo erectus. The frontal bone shows a robust temporal line and thick cranial wall. Besides, the frontal bone has a metopic suture and enlarged frontal sinus. The occlusal surface of the molar has cusp 5, cusp 6 and cusp 7 plus complicated occlusal morphological pattern. Crown dimensions are within variations of Homo erectus and much larger than those of early modern human, contemporary human and European Middle Pleistocene humans. With these feature patterns, we proposed they may represent Homo erectus living during the Middle Pleistocene. In addition, the three pieces of Hualongdong femurs exhibit mosaic patterns with resemblance to Middle Pleistocene archaic hominins and Late Pleistocene early modern humans respectively, including lacking a pilaster, subtrochanteric pieces similar to Middle Pleistocene, and a prominent gluteal buttress and a small third trochanter resembling to many Upper Paleolithic hominins.

These morphological patterns suggest that the 300 ka Hualongdong hominin fossils already exhibit the evolutionary trend towards the modern humans, and the Hualongdong hominins are the earliest Middle Pleistocene hominins in East Asia with most modern human features. The discoveries and related studies of Hualongdong hominin fossils provide new evidence for the hominin evolutionary diversities of East Asian late Middle Pleistocene.

Key words: Hualongdong site, hominin fossils, human evolution, modern human origin, late Middle Pleistocene