New Late Pleistocene age for the Homo sapiens skeleton from Liujiang southern China

Domain: earth_science
Published: 2024-04-29
Editorial outcome: minor_revision

Abstract
The emergence of Homo sapiens in Eastern Asia is a topic of significant research interest. However, well-preserved human fossils in secure, dateable contexts in this region are extremely rare, and often the subject of intense debate owing to stratigraphic and geochronological problems. Tongtianyan cave, in Liujiang District of Liuzhou City, southern China is one of the most important fossils finds of H. sapiens, though its age has been debated, with chronometric dates ranging from the late Middle Pleistocene to the early Late Pleistocene. Here we provide new age estimates and revised provenience information for the Liujiang human fossils, which represent one of the most complete fossil skeletons of H. sapiens in China. U-series dating on the human fossils and radiocarbon and optically stimulated luminescence dating on the fossil-bearing sediments provided ages ranging from ~33,000 to 23,000 years ago (ka). The revised age estimates correspond with the dates of other human fossils in northern China, at Tianyuan Cave (~40.8–38.1 ka) and Zhoukoudian Upper Cave (39.0–36.3 ka), indicating the geographically widespread presence of H. sapiens across Eastern Asia in the Late Pleistocene, which is significant for better understanding human dispersals and adaptations in the region.

Introduction
Dating of hominin fossils and their localities places the origin of Homo sapiens back to ~310 ka in Africa1 and documents dispersals out of Africa and into the Levant and southeastern Europe to more than ~180 ka2,3. Recent advances in understanding the biological and cultural evolution of modern human populations2–4 highlight the need to clarify the history of H. sapiens in the East Asian mainland. However, fossils of H. sapiens in this region with clear stratigraphic contexts and precise chronological age controls are scarce. Though there have been claims for H. sapiens in China before 80 ka5–7, the taxonomy and ages of these finds have been contentious8,9. More secure knowledge of early modern human history in the East Asian mainland rests on remains from Tianyuan Cave (40.8–38.1 ka cal BP)10 and the casts of the lost fossils from Zhoukoudian Upper Cave (39.0–36.3 ka cal BP)11 in northern China, and by young fossils of Pleistocene-Holocene transition from Longlin cave (11.5 ka cal BP)12, Maludong (14.3–13.6 ka cal BP)12, and Dushan cave (15.9–12.8 ka cal BP)13 in southern China.

Among key fossil evidence in China, the Liujiang hominin has assumed great importance owing to the fact it is one of the most complete H. sapiens skeletons. Moreover, the skeletal remains are thought to represent a late Middle Pleistocene/early Late Pleistocene presence of modern humans in Eastern Asia, even earlier than their arrival in western Eurasia. Though the Liujiang skeletal elements are generally well preserved, the provenience and dating of the fossils have been contentious since they were first found more than six decades ago14–16.

The Liujiang materials were originally recovered in September 1958, in a cave called Tongtianyan by workmen digging for phosphorous fertilizer17 (Fig. 1). After the human fossils were discovered, paleoanthropologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Beijing, immediately travelled to the cave to conduct initial investigations. The human fossils were found near the entrance of the cave (Fig. 1c). The surveyors found that only a small part of the deposits were still intact, consisting of limestone breccia and unconsolidated sediments, including a layer in which vertebrate fossils were recovered. Unfortunately, the exact position of the human fossils was unclear given the intensity of the digging by the work crews. At the time it was noted that the human cranium was likely embedded in unconsolidated breccia, which was markedly different from the consolidated deposits containing the vertebrate fossils. In addition, no artefacts have ever been recovered from Tongtianyan, indicating that the cave was not an occupation site.

The Liujiang human fossils are composed of an early complete cranium and 17 postcranial elements, including vertebrae, ribs, a sacrum, the os coxae, and femora17. The cranial volume is 1567 mL. The right and left zygomatic arches are broken. The teeth and palate are moderate in size, with a shovel-shaped right lateral incisor17. There is a congenital absence of both upper third molars and the loss of the upper left central incisor and upper left second molar crowns. The vertebrae include the inferior four (the ninth to twelfth) thoracic vertebrae and all five lumbar vertebrae. Four articulating rib fragments are attached to the thoracic vertebrae. The sacrum is still attached to the fifth lumbar vertebra and could articulate with the right os coxae by the auricular surface. The right femur is represented by the diaphysis of the most proximal to middle-distal region while the left one is represented by the diaphysis of the proximal to middle region.

The Liujiang materials were attributed to a single individual based on the similar colour of the bones, the similar degree of fossilization, and the lack of duplication of anatomical parts17. The degree of cranial suture closure and the dental occlusal wear indicate that the individual was an adult, approximately 40 years old17. The upper two-thirds of the sacrum is relatively straight with the tail being curved anteriorly. The sciatic notch has a relatively small posterior potion. The characteristics of the os coxae, in combination with the cranial features suggest that the individual is a male17,18.

Human fossils are generally rare and/or partial across East and Southeast Asia. For instance, although Tianyuan Cave preserves postcranial bones, the cranium is absent13. Salkhit is represented only by a skullcap, Tam Pa Ling has two mandibles, an incomplete cranium and other postcranial fragments, and the Deep Skull from Malaysia’s Niah Cave is also incomplete19–23. The human remains from the Tabon Cave in Philippines have cranial fragments, two partial mandibles, and other limb fragments24,25. The Wajak materials from Indonesia are mainly known for a relatively complete cranium and a partial skull26. In contrast to these fragmentary fossil finds, the Liujiang individual retains a complete cranium, as well as vertebrae, ribs, femora, and pelvic bones that are absent at several other sites. As one of the most complete fossils of H. sapiens in China, the Liujiang skeleton provides crucial information about the morphology and evolution of modern humans in Eastern Asia. The Liujiang individual exhibits a series of modern human-like features, such as a globular cranium, a reduced and flat face, a round brain case with an enlarged cranial volume, small teeth with simple occlusal surfaces, and a slim body shape17,27–29. Among the cranial features, the short and broad face and the rectangular orbit are the traits that are rarely expressed in recent modern humans, but commonly found in early modern human fossils17,30,31. In comparison to other Eurasian early modern humans, Liujiang has some distinct features, including a bulged frontal squama, protruded superciliary arches, a low nasal bridge, and an occipital bun32. There is a general agreement that the Liujiang cranium can be separated from that of modern human finds from Zhoukoudian Upper Cave in both metrics and non-metrics30,31,33. In comparison to Liujiang, the cranium of Zhoukoudian Upper Cave retains more primitive and robust characteristics. As a derived form, the Liujiang cranium is more rounded and has a less developed supraorbital torus, sagittal keel, occipital torus, mastoid process, zygomatic triangle, and zygomatic tubercle than that of Zhoukoudian Upper Cave31,32. A regional population affinity for Liujiang was based on features including facial flatness, the orientation of the broad and low nose, rounding of the lower outside borders of the orbits, large and protrusive zygoma, shoveling of the incisors, and a congenital absence of a third molar17,28,34. However, this point of view was challenged by a craniometric analysis that demonstrated that the Liujiang individual could be distinguished from modern regional populations30. On the basis of other craniometric studies, the Liujiang cranium was shown to be morphologically divergent from Moh Khiew, Thailand, dated to 25.8 ka cal BP35, but similar to Minatogawa 1, Japan, dated to ~18.3–16.6 ka 36. A geometric morphometric study of cranial shape indicated that Liujiang was similar to Cro-Magnon 132, dating to ~33–31 ka 37.

Since the discovery of the hominin fossils, two independent radiometric dating projects have been conducted14–16. Using conventional radiocarbon and classic α-counting U-series dating methods, Yuan and colleagues15 obtained a 14C age of 3.0 ± 0.2 ka cal BP for the flowstone near the cave entrance, a U-series age of 67 +6/−5 ka for the thick flowstone on top of Unit II (see Supplementary Information, section 1.2), and U-series ages ranging between 227 and 95 ka for the mammalian fossils. The investigators suggested that the human fossils were older than ~67 ka, but they noted that this age estimate remained to be verified given the uncertain provenience of the finds. A later attempt to establish the age of the Liujiang deposits was by Shen and colleagues14,16 using α-counting and thermal ionization mass spectrometry U-series methods to date the flowstones from various depositional units and mammalian fossils. The researchers concluded that the human fossils dated to at least ~68 ka and more likely to ~139–111 ka if they came from the filling breccia. Given the combination of early ages, the Liujiang skeletal remains have been considered to be among the earliest fossil representatives of H. sapiens in China, and therefore, the hypothesis of regional continuity of human populations in the area was thought to be strengthened38. Yet, the late Middle Pleistocene to early Late Pleistocene dating results have been considered surprisingly old given the modern morphological features of the human fossils31.

Tongtianyan cave (24°10′59″N, 109°25′56″E, 164 m above mean sea level) is situated on the western slope of a karstic limestone mountain in Liujiang District of Liuzhou City, ~180 km northeast of Nanning, the capital of the Guangxi Province. Geological and stratigraphic observations indicate that the sedimentary sequence in the cave can be divided into three major units (I–III) that are irregularly bedded from bottom to top (Fig. 2). Unit I is composed of a light gray tilt-bedded fine sand interbedded with thin layers of yellow clay covering the cave bottom and irregularly underlying Units II and III. Unit II, approximately 3.6 m-thick, consists primarily of yellowish-brown bedded calcareous clay/silty clay and silty clay interbedded with several flowstone layers. Most of Unit II is exposed along the north side of the cave, with a small amount on the south side. Well-preserved mammal species fossils were recovered from Unit II14,17 including Ailuropoda melanoleucus, Rhinoceros sinensism, Stegodon orientalis, Megatapirus sp., Sus sp., Bovidae and Cervidae. These fossils are the common members of the late Middle Pleistocene Ailuropoda-Stegodon fauna of southern China39,40. Unit III has a thickness of 3.8 m and mainly consists of brown gravel and yellowish-brown clay capped by a flowstone layer. It fills in the gully cutting through Unit II, part of which irregularly overlies the upper part of Unit II. Unit III can be subdivided into five layers from top to bottom (Supplementary Information, section 2). The yellowish-brown clay sediments cemented on the human fossils suggest that Unit II and upper part of Unit III could be the potential human-fossil bearing stratigraphy, rather than the coarse breccia layer as previously suggested14.

The previous early age estimates of Liujiang skeletal remains have assumed great importance in the paleoanthropological record of China, with significant implications for human evolution and the timing of out of Africa dispersals41,42. Precise dating for the Liujiang skeletal remains is therefore crucial for determining its evolutionary position and disentangling the long-standing debate on the timing of modern human occupation of the East Asian mainland. Here, we show detailed sedimentological and geochemical comparisons between the sediments from the Liujiang human fossils and those from various depositional units at Tongtianyan cave to determine the origin of the human specimens. Subsequently, we combine 14C, U-series and optically stimulated luminescence (OSL) dating of the human and mammalian fossils, and sedimentary deposits to provide age constraints on this critical early modern human skeleton.

Results
Sediment characteristics and provenience of the human fossil remains
To pinpoint the provenience of the Liujiang human fossils, sediment samples were extracted from the medullary cavity of the Liujiang femur for Sr-Nd isotopic (Supplementary Table 1), trace element (Supplementary Data 1), grain-size analyses and colour assessment, allowing for a comparison to other depositional units within the cave.

The Sr-Nd isotopic composition of the sediments from the human fossils (LJHS) clearly differed from the sediments of Unit II and Layer 5 of Unit III (Fig. 3a, Supplementary Table 1), thereby excluding these as a potential provenience for the fossils. The rare element ratio plots and ternary diagrams (Supplementary Fig. 5b–i) show that the LJHS results are most similar with the samples from Layers 2 and 3 of Unit III, but significantly different to those from Unit II and Layer 5 in Unit III. Sediment grain-size and colour analyses also show that the LJHS data are most closely related to Layer 2 of Unit III (Fig. 3b, c, Supplementary Fig. 3). Thus, multiple lines of evidence point to the reddish-brown clay of Layer 2 of Unit III as the burial environment for the human fossils.

The Layer 5 of Unit III, previously proposed as the origin context14,16, can categorically be excluded unless the fossils have been reworked and redeposited. The articulation of the vertebrae, with no trace of gnawing or abrasion on the human fossils, seems to exclude the possibility that the human fossils were buried in the sandy gravel layer or underwent post-depositional transport; instead, the articulations favour an interpretation of burial in a low-energy depositional environment without significant transport.

Dating results
We then established a chronologic framework for the stratigraphy based on radiocarbon, OSL and U-series dating (see Supplementary Materials 4, 5 and 6). U-series dating on the capping flowstone, Layer 1 of Unit III, yielded ages of ~16–14 ka (Supplementary Fig. 6, Supplementary Data 2), similar with the radiocarbon dates of ~14–13 ka cal BP obtained from charcoal and organic sediment in this layer (Supplementary Table 2). U-series dating on the flowstone on the top of Unit II resulted in an age of ~63 ka (Supplementary Fig. 6, Supplementary Data 2), consistent with previously published results14. Quartz OSL dating results of the samples from Unit III ranged from ~53 to 22 ka (2σ uncertainty range), which are stratigraphically coherent and broadly consistent with the U-series (Fig. 2, Supplementary Data 2) and radiocarbon ages (Fig. 2, Supplementary Table 2). Due to the saturation of the luminescence signals, samples from the upper and lower parts of Unit II provided only minimum ages of at least 54 ka and 106 ka, respectively.

The U-series results from the flowstones, the radiocarbon and the OSL age estimates from Unit III (Supplementary Data 3 and Supplementary Data 4) were combined with stratigraphic information to develop a Bayesian age model (Fig. 4a, b, Supplementary Code 1). Details of samples, preparation, measurement, and data-analysis procedures are in Supplementary Materials (section 6.2). The Bayesian analyses indicate that Unit III started to accumulate from 52.2 ± 11.0 ka (henceforth all age estimates are given with 2σ uncertainties) with an end date of 11.6 ± 1.6 ka. This is supported by the U-series results of the thickest flowstone overlying Unit II (63.1 ± 0.3 ka) and on the capping flowstones of Unit III (Layer 1, ~16–14 ka). Layers 3 and 2 span from 39.4 to 37.2 ka and from 32.5 to 22.6 ka, respectively. The boundary between Layers 3 and 2 was modelled from 37.2 ± 5.2 ka to 32.5 ± 2.5 ka (Fig. 4b, Supplementary Data 5), consistent with the U-series isochron age of 37.8 ± 8.6 ka obtained from a dirty flowstone sample (LJ20-FS3) located between Layers 2 and 3 (Supplementary Fig. 6, 7). Therefore, the best age estimate for the fossil-bearing Layer 2 is between 32.5 ka and 22.6 ka.

Fossil bone readily takes up uranium from ground water post deposition although the process can be relatively slow; therefore, U-series dating of fossil bone allows estimation of a minimum burial age, provided U-leaching has not occurred43. U-series dating analyses on the Liujiang human fossils were first carried out on two small dentine fragments fallen from the upper central incisor, and some bone splinters produced during a previous sample extraction from the left femur (Figs. 5a-1–3). The dentine sample yielded U-series apparent age of 18.72 ± 0.10 ka, and the two bone sub-samples 22.85 ± 0.04 ka and 21.64 ± 0.04 ka, respectively. The difference between the dentine and bone U-series ages (~3–4 ka) is likely the result of the fact that the dentine was in an open system for a longer period of time.

We further undertook U-series analyses along two profiles on the left femur to check for diffusion processes. Two parallel profiles consisting of nine and eight subsamples (LJ20-1 to 9 and LJ20-(1) to (8)), respectively, were hand-drilled sequentially from the inner to the outer surfaces on the cortical bone section (~6 to 7 mm thick, Figs. 5a-4, 5). U-series analyses show that the 234U/238U and 230Th/238U activity ratios are in the narrow ranges of 1.189–1.195 and 0.218–0.228, respectively, and U-series apparent ages are between 21.4 and 23.3 ka (Figs. 5a-5). The U-series isotopic ratios and apparent ages all display U-shaped profiles across the bone section (Fig. 5b), which conform to the distribution patterns predicted by the D-A (diffusion and adsorption)44,45 and DAD (diffusion-adsorption-decay) models43. For the two profiles, the DAD model yielded consistent results: maximum likelihood minimum ages of 23.8 ± 0.7 and 24.0 ± 0.8 ka with initial 234U/238U activity ratios of 1.192 and 1.191. Therefore, we consider that the Liujiang human fossils have a burial age of at least 23.9 ± 0.5 ka.

Tongtianyan cave has long been seen as a site demonstrating the co-existence of H. sapiens alongside Ailuropoda-Stegodon fauna during the Late Pleistocene of south China34, reinforcing evidence for the deep antiquity of the human fossils. Previous U-series dating of seven fossil teeth ranged from 227 to 95 ka14,16. We collected eight mammalian fossil teeth for U-series dating to test this relationship. Among them, one fossil tooth was recovered in the sediments adhering to the cave ceiling and seven from the disturbed sediments as a consequence of digging for fertilizer (Supplementary Fig. 8, Supplementary Data 2). The newly sampled mammalian fossil teeth gave 234U/238U and 230Th/234U activity ratios and apparent ages comparable to the previous results (Figs. 5c-1, Supplementary Data 2). However, the human fossils were distinct from the mammalian fauna in terms of U-series isotopic ratios and apparent U-series ages (Fig. 5c), indicating that there is no association between the human fossils and the Ailuropoda-Stegodon fauna.

In sum, provenience and dating studies have been conducted on the flowstone, sediments and the human and mammalian fossil remains. Our proveniencing results indicate that the Liujiang human fossils derived from Layer 2 of Unit III. Layer 2 ranged from 32.5 ± 2.5 to 22.6 ± 7.4 ka using Bayesian analysis on radiocarbon, OSL and carbonate U-series ages. U-series dating on the human fossils provided a minimum age of 23.9 ± 0.5 ka, falling into the age range for Layer 2. Collectively, the age of the Liujiang human fossils can be constrained to ~33–23 ka. The mammalian fossils dated to between 227 ka and 95 ka by U-series methods14–16 indicate a significant hiatus between the deposition of the Ailuropoda-Stegodon fauna and the human remains.

Methods
Sample extraction from the Liujiang human fossils, and from the stratigraphy of the Tongtianyan cave has been permitted by the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, and Liuzhou Lotus Cave Science Museum. Results of this study will be shared with the Liuzhou Lotus Cave Science Museum, following the strategy for information sharing that we established prior to starting fieldwork in 2019.

Radiocarbon dating
A single piece of charcoal and two organic sediment samples from Layers 1 and 2 of Unit III were collected and submitted to the BETA Analytic laboratory (Beta-) and Peking University (BA-) for radiocarbon dating. These samples were pretreated using routine acid-alkali-acid and acid-washing methods, separately. In addition, a bone sample of 402.2 mg (R-EVA382) cut from the Liujiang femur was also pretreated at the MPI-EVA, Department of Human Evolution, Leipzig, following the method for collagen extraction and purification, including an ultrafiltration step, as described in Talamo and Richards59. However, the collagen retrieval failed due to its poor preservation (Sahra Talamo and Qiaomei Fu, personal communication).

The dates were reported in radiocarbon years BP (Before Present-AD 1950) using the half-life of 5568 years (in Supplementary Table 2). Isotopic fractionation was corrected for using the δ13C values measured on the AMS. The quoted δ13C values were measured independently on a stable isotope mass spectrometer (to ±0.3 per mil relative to VPDB). The new 14C determinations were calibrated using the INTCAL20 calibration curve60 and the OxCal 4.4 platform61,62, with age ranges expressed at the 95.4% confidence interval. All other previously published radiocarbon dating data cited in this work have also been recalibrated using the INTCAL20 calibration curve.

U-series dating
The U-series dating analyses were carried out at the laboratory of Nanjing Normal University. For bones and teeth, the samples were weighed and dissolved with 3N HNO3 in Teflon beakers. A quantity of a 229Th-233U-236U triple spike was then added into sample solutions. The sample-spike mixture was heated overnight on a hot plate at 120 °C. After the equilibration of the sample-spike mixture, U and Th were separated from each other and from other cations by passing the sample solution through a U-TEVA resin column following the procedure of Douville et al. 63. Firstly, the sample matrix elements were eliminated through rinsing with 3N HNO3. Subsequently, Th was eluted using 3N HCl, and finally, U was eluted using 0.5N HCl. One drop of HClO4 was added to the U or Th fractions to remove any organic material derived from the U-TEVA resins. The U and Th solutions were evaporated to dryness and then dissolved in a mixture of 0.5N HNO3 and 0.01N HF for U and Th isotopic analyses. The protocol used for the flowstone samples was similar, with the U-Th co-precipitation with iron hydroxide prior to passing the U-TEVA resin column.

The U and Th isotopic measurements were performed on a Thermo Fisher Neptune MC-ICPMS (multi-collectors inductively-coupled plasma mass spectrometer). It is equipped with nine Faraday cups and a secondary electron multiplier (SEM). A retarding potential quadrupole (RPQ) energy filter was positioned in front of the SEM. An Aridus-II desolvator system (Cetac) coupled with an ESI-50 nebulizer and an Auto-Sampler (ASX-520) were used for sample introduction. The U-Th data acquisition strategies applied here were similar to those described by Shao et al. 64. The U isotopic data were acquired in two static sequences. The first sequence measured 233U, 235U, 236U and 238U in cups and simultaneously 234U on the SEM (with RPQ-on). The second sequence shifted all masses by 1 amu to the lower mass, so that 233U was measured on by the SEM and the other isotopes were by the cups. Thorium measurements were carried out immediately after the uranium measurements for the same sample. 229Th and 230Th were measured alternately on the SEM (with RPQ-on) and 232Th in a cup. The U isotopes of the Harwell uraninite HU-1 standard solution, which is widely used standard at secular equilibrium state, were measured after every 3 samples to monitor external reproducibility.

The amplifier gains, dark noise, hydride interferences and machine abundance sensitivity were evaluated every day prior to the sample measurements. The baselines were automatically calibrated before each U isotopic measurement. Instrument memory was assessed with the SEM by introducing a blank solution before measurements of either U or Th were conducted. The relative yields of the SEM/Faraday cups were determined during U isotopic measurements by alternating the 233U beam (~5 mV) on the SEM and in the Faraday cup. Instrumental mass fractionation was corrected by using an exponential function by comparing the measured 238U/235U with the natural value of 137.82 for unknown samples65. Procedural blank was corrected by using the long-term observed values of ~0.8 fg 234U, ~10 pg 238U, ~0.1 fg 230Th and ~2.0 pg 232Th, respectively. The U-series ages were calculated by Monte-Carlo simulations64, using half-lives of 75,584 a for 230Th and 245,620 a for 234U66, 1.4 × 1010 a for 232Th67, and 4.47 × 109 a for 238U68. The fossil samples and the carbonate samples from the capping flowstone were corrected with the assumption of an initial 230Th/232Th activity ratio of 0.8 ± 0.4, which is a value for a material at secular equilibrium with the bulk Earth upper crustal 232Th/238U atomic ratio of ~3.869.

Luminescence dating
The optically stimulated luminescence dating technique determines the time elapsed since the last sunlight exposure of a deposit, i.e., its burial time, which was first introduced by Huntley and colleagues70 and has been widely used to date geological and archaeological deposits71–74 in recent decades. The luminescence emitted from minerals (e.g., quartz and feldspar) under artificial light exposure is proportional to the absorbed energy accumulated within the crystal lattice of minerals by ionizing radiation (e.g., alpha, beta or gamma radiation) from radioactive elements such as uranium (U), thorium (Th), Rubidium (Rb) and potassium (K) in the environment, as well as cosmic rays73,75. By comparing natural luminescence signals with signals generated after known laboratory irradiation doses, the total radiation dose absorbed by mineral grains over the burial time (or equivalent dose, De) is determined. The assessment of the natural environmental irradiation dose rate, to which the sample is exposed during its burial history, involves measuring the radioactivity of the sample and its surroundings using chemical and radiometric methods, and estimating the radiation contributed by cosmic rays. The luminescence age of sediments is then achieved by dividing the equivalent dose (Gy) by the dose rate (Gy/ka)76.

To provide further age constraints on the Tongtianyan sequence, eleven sediment samples (Supplementary Fig. 1a) were collected from Units II and III of the Liujiang sequence for OSL dating by hammering steel tubes (20 cm-long cylinders with a diameter of 5 cm) into a freshly dug vertical section. The tubes were then covered and sealed with aluminum foil and wrapped in black plastic bags and taped to avoid light exposure and moisture loss. The sediments from the potential light-exposed end of the cylinder were removed and those from the middle of the cylinder was used for De measurement.

As suggested by the grain-size analyzes, coarse-grain fraction (>63 μm) was scarce in most of these samples, fine-grain (4–11 µm) quartz OSL dating was applied for the min this study. The raw samples were first etched with 10% hydrochloric acid and subsequently with 30% hydrogen peroxide to remove carbonates and organic matter. Subsequently, the chemically treated sediments were then suspended in a column of 0.01 N sodium oxalate to disperse for 20 min according to Stokes Law to remove the >11 mm fraction. This procedure was then repeated for longer 4 h periods to isolate the desired 4–11 µm poly-mineral fraction. To extract pure fine-grain quartz grains for OSL dating, these fine silt fractions were mostly etched using the 30% H2SiF6 (hydrofluorosilicic acid) for 4 days, except for samples HED-628 and HED-683, etched only three days to reduce the risk of loss of quartz due to its small sample size. The purity of the quartz extracts was confirmed by the absence of a significant infrared stimulated luminescence (IRSL) response at 60 °C to a large regenerative β-dose. Dispensing 2 mg of this fraction (4–11 µm quartz), it then suspended in small tubes with distilled water, and then was settled on each 10 mm diameter stainless steel disc for luminescence measurements. Sample preparation was carried out in the IVPP laboratories.

Luminescence measurements were made on a Risø Model DA-20 TL/OSL reader equipped with a 90Sr/90Y beta source for irradiation77 and an EMI 9235QA photomultiplier tube. Blue light LED (470 ± 30 nm) stimulation set at 90% of 50 mW cm−2 full power and 7.5 mm Hoya U-340 filters (transmission between 290 and 370 nm) were used for the quartz OSL measurements. The beta sources of the readers were calibrated using standard Risø calibration quartz (RCQ)78,79 with a batch number of 108 and a correction of ~8.25% was performed80. Source calibrations were carried out using 4–11 µm fine-grained quartz grains on stainless steel discs.

The single-aliquot regenerative-dose (SAR) protocol was used to determine the De value81–83 (Supplementary Table 3). A test dose of 30 Gy, 20–30 percent of natural dose was used for De determination. After the standard SAR protocol, a repeated regenerative dose measurement was applied to determine the recycling ratio. In addition, to test the purity of the quartz extracts, an additional recycling step was given at last to each aliquot, in which IR stimulation of grains for 40 s at room temperature using infrared LEDs was set after preheat and prior to blue light stimulation. The OSL signals of the first 0.8 s (channels 1–5) integral after late background subtraction from the last 4 s (channels 225–250) were used for dose response curve construction84. These measured aliquots which having the recycling ratio or OSL IR depletion ratio exceeding the acceptable range (0.9–1.1), or with the recuperation over 5%, were excluded from the De determination83,85. For each sample, there were only ~1–2 aliquots (0.5–0.7%) that failed to meet the above criteria, and these were rejected for De determination. Finally, 14–40 aliquots were accepted for De determination of each sample, and the arithmetic mean was used for De calculation of each sample.

Prior to the routine application of the SAR protocol, several laboratory tests were carried out on the extracted quartz grains. Firstly, to select an appropriate preheat temperature for De determination, preheat plateau tests for two representative samples (HED-640 from Layer 2 and HED-682 from Layer 4) were conducted. The preheat temperature varied from 160 °C to 300 °C at 20 °C increments, with the cut-heat ranged from 160 °C to 260 °C at 20 °C increments basically tracking and lagging the preheat temperatures by a margin of 40 °C86; for each preheat temperature step, the mean De value of three aliquots was calculated. To confirm the suitability of measurement conditions, a dose recovery test for fine-grain quartz using the SAR protocol outlined in Supplementary Table 3 was also carried out on 8 samples with given doses ranging between 110.2–142.6 Gy. For the other three samples including HED-626, HED-638 and HED-639 from the Unit-II with the quartz completely saturated, dose recovery tests were not conducted. At least three aliquots for each sample were first bleached twice at room temperature for 100 s with blue LEDs, with a pause of >5000 s in between to avoid any charge transferred to the 110 °C thermoluminescence (TL) trap. A known beta dose approximating the natural dose was then administered to each aliquot, and the same approach as the De measurement was used to recover this known dose. The dose recovery ratio was then determined by dividing the measured De by the given dose (Supplementary Fig. 9). Finally, a preheat temperature of 260 °C and a cut-heat at 220 °C were used for De determination of all samples.

To determine the environmental dose (from natural 238U, 232Th, 226Ra and their decay products, and 40K) of these OSL samples, sediments from a 30 cm radius around the sampling tubes were collected for dosimetry measurements and water content. The specific activities of radionuclides including 238U, 226Ra, 232Th, 210Pb and 40K were mainly measured using high-resolution gamma γ-spectrometry (HRGS)87. Firstly, the bulk samples were dried at 60 °C and ground for homogenization. Then, about 280–300 g dry powder sediments for each sample were sealed into a plastic container and stored for 1 month to build up equilibrium between 222Rn and 226Ra before determining the activities of natural U, 232Th and their daughter nuclides and 40K. All samples were measured for 24 h using a high-purity germanium detector (ORTEC GEM 70P4-95, P-type, 70% relative efficiency, 122 kev FWHM at 1.0 kev and 1.332 Mev FWHM at 2.0 kev) shielding in low-activity lead to minimize the influence of environmental radioactivity. In addition, a field γ-spectrometer with a NaI detector was also used to estimate the in-situ gamma dose rate at the sample location to reduce the effect of heterogeneous sediments and the effect of Rn escape. Each sample was measured for 8 h in the field. Spectral data were converted to activity concentrations and infinite matrix dose rates using conversion data by Guérin et al. 88. The cosmic dose contribution was estimated by taking account of the burial depth of the sample, the thickness of the cave roof overhead (12.5 m), the zenith-angle dependence of cosmic rays, and the latitude, longitude, and altitude of the site89. Water content (moist mass/dry mass) was determined by weighing the sample before and after drying and was assigned an absolute uncertainty of ±3%. Subsequently, using the dose rate conversion factors of Guérin et al. 88 and water content attenuation factors76, the radioactive element concentrations were converted into an effective dose rate. The alpha dose was calculated using an alpha efficiency value of 0.04 ± 0.02 according to Rees-Jones90. The beta grain size attenuation factors from Guerin et al. 88 were used for beta dose rate calculation. Finally, dose rates and ages were calculated with the ager program91.

Bayesian age modelling of the Tongtianyan cave deposits
To establish a chronological framework for the depositional units at Tongtianyan cave, we conducted Bayesian analysis that includes the radiocarbon, OSL and carbonate U-Th dating data, using OxCal v4.461,62. All 14C ages were calibrated using the INTCAL20 dataset. For all the OSL and U-series ages, we used N_date in calendar years before AD 2022 with associated 1σ errors as likelihood estimates. Additionally, the U-series dates for the Liujiang human fossils were also included in the model as minimum age estimates using a Before command. To estimate the posterior distributions (i.e., the modelled ages), the stratigraphic order of each sample was input using the Sequence function (Supplementary Code 1), based on the assumption that a sample stratigraphically lower is older than those above. For samples that are from the same stratigraphic layer with similar depth or with ambiguous stratigraphic orders, such as Layers 3, 2 and 1, they were modelled as a Phase, in which the measured ages are assumed to be part of a single phase. For the layers with abrupt and clear boundaries between them, such as between Layers 3 and 2, or Layers 2 and 1, upper or lower Boundaries were placed for them to constrain their start or end ages. Otherwise, for layers for which gradual stratigraphic changes were identified, assuming continuous sediment accumulation, transitional boundaries were placed between them. The samples, phases and sequences were arranged according to their relative stratigraphic order.

We applied the general t-type outlier model92 to detect outlier ages by assessing the likelihood of each age being consistent with the modelled ages. A prior outlier probability of 5% was assigned for the other samples with their posterior outlier probability calculated during the modelling process. The codes used to run the Bayesian model are listed in Supplementary Code 1. The generated probability distribution functions (PDF) for each of the samples are shown in Fig. 4b and their corresponding 95.4% probability ranges are summarized in Supplementary Data 5. As demonstrated in Fig. 4b, the Bayesian model results in improvements in the precision in age estimates for all the samples. None of the samples was flagged as an outlier, as indicated by the posterior outlier probabilities, which are less than 4% for all samples. The model is shown in Supplementary Information section 6.2.

Sr-Nd isotopic analysis
Five representative samples were analyzed for Nd-Sr isotopic and trace element analysis, including the samples of LJHS and one each from Layer 2 (HED-628), Layer 3 (HED-627) and Layer 5 (HED-683), as well as one from the Unit II (HED-626). The silicate Nd-Sr isotopic ratios of the samples were determined by a Finnigan Neptune MC-ICP-MS at the Nanjing University following the method of Chen et al. 93. About 1 g of powdered sample was treated with purified acetic acid solution (0.5 mol/L) at room temperature for up to 8 h to remove the carbonate and then heated at ~600 °C for 8 h to remove organic matter. Subsequently, ~0.1 g of this treated sample was transferred to Savillex vials to digested with acids (2 mL of HNO3 + 1 mL of HF) at 100 °C for 24 h and dried. About 3 mL of aqua regia was added to the dried sample and sealed vials were heated at 110 °C for ~12 h. After addition of 3 mL of 2N HCl in steps, the vials were kept at 110 °C for drying, following which the samples were ready for ion exchange column chemistry. Standard ion exchange protocols were followed for the separation of pure Sr and Nd fractions. The 87Sr/86Sr and 143Nd/144Nd ratios were then measured on a MC-ICP-MS. The analytical blanks are insignificant: <1 ng for Sr and <50 pg for Nd, respectively. Reproducibility and accuracy were checked by running the strontium standard SRM NBS 987 and neodymium standard La Jolla, with mean 87Sr/86Sr of 0.710264 ± 0.000013 (external ± σ, n=10) and mean 143Nd/144Nd of 0.512121 ± 0.000007 (external ± σ, n=10) respectively.

Trace element analysis
Five samples for trace element analysis were leached of calcium carbonate using 1 mol/l acetic acid (HAc) to totally leach the carbonate fraction without significant effect on silicates or iron oxides. Before acid dissolution, all samples were finely ground using an agate mortar. Then, 40 mg these samples were dissolved in Teflon bombs with a stainless steel jacket with 0.3 mL HNO3 and 1 mL HF added. After being shaken with ultra-sonic device for 10 min, the bombs were placed on a hot plate (170 °C) for 15 h. The solutions were then dried, and a HNO3-HF solution was added. The bombs were again placed on a hot plate (20 °C) for 7 days. After the solutions were dried, 3 mL HNO3 was added, and the bombs were placed on a hot plate (170 °C) for 5 h. The solutions were then evaporated, dissolved in 3 mL HNO3 and placed on a hot plate for 5 h. The solutions, after cooled, were then transferred into 50-mL volumetric flasks, and 1 mL 500 mg/L Indium solution was added as the internal standard. The final solutions were diluted by 1% HNO3. The trace element compositions were determined using an ICP-MS (ELEMENT, Finnigan MAT) in the Nanjing University. The rhodium solution (10 ppb) was dropped into the sample solutions for instrument drift correction during the measurements. The analytical uncertainties are less than 5% for each element.

Grain size analysis
Nineteen sediment samples including eleven OSL samples and eight bulk samples from the three sedimentary units on the Liujiang section, and one bulk sample from the sediments trapped in the cavity of the Liujiang femur, were collected for grain-size analysis (Supplementary Fig. 1). These samples were firstly pretreated with 30% hydrogen peroxide (H2O2) to remove organic matter, and then treated with 10% hydrochloric acid (HCl) to remove carbonates. Subsequently, the samples were dispersed with 0.5N sodium hexametaphosphate ((NaPO3)6). Grain-size was determined using a Malvern Mastersizer 3000 particle analyzer with an analytical precision of <1%. The Mie theory was applied with a particle refractive index of 1.520.

Colour analysis
All the nineteen sediment samples were dried at 50 °C and ground to a powder for colour analysis. The measurements were conducted using a Courtney Minolta CM-400 colorimeter under standardized observation conditions (2° Standard Observer, Illuminant C), with a D65 standard light source. The spectral information was converted into the CIELAB Colour Space system (CIE 1976). The L*a*b* values indicate extinction on a scale from L*0 to L*100, and express colour as chromaticity coordinates on red-green (a*) and blue-yellow (b*) scales.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_2": "New Late Pleistocene Age for the Homo sapiens skeleton from Liujiang, southern China\nThe new dating of the skeletal remains from Liujiang cave is a useful addition to our knowledge of the\nhistory of H. sapiens in China. The account of the dating is detailed, thorough and convincing, and\nshould end any controversy over the age of this material. The description of the skeletal evidence is\nalso useful and provides a more up-to-date overview of its coverage in the Wu and Poirier 1995\nvolume Human Evolution in China (Oxford 1995).\nRegarding publication in Nature, my main concern is that Liujiang has now lost its international\nsignificance. Its new dating at 33-24 ka brings the skeleton in line with other East Asian finds, such as\nSalkhit, (Mongolia), Upper Cave, Zhoukoudian, Moh Thiew (Thailand); and shows that it is younger\nthan the specimens from Tianyuandong, North China, Niah Cave, Borneo and Tam Pa Ling, Laos, all of\nwhich are >40 Ka. As a result of the re-dating, Liujiang is now in the category of “interesting but not\nvery important” in international terms. I therefore think it is inappropriate for Nature. There is no\ndoubt that this is an excellent paper; however, it is one that has a regional but not international\nsignificance.\nThe redating and skeletal descriptions are certainly worth publication in a journal such as Journal of\nHuman Evolution, where the new evidence can be read by the relatively small community familiar with\nthe human skeletal record of China and SE Asia.", "reviewer_5": "Dear Authors,\nThank you for the opportunity to read your manuscript NCOMMS-23-34915-T “New Late Pleistocene\nAge for the Homo sapiens skeleton from Liujiang, southern China”. I have been invited to share my\nthoughts on a broader level for the manuscript, which I am doing in the following, I will not comment\nmuch on individual items raised by your four other excellent reviewers. I am glad to see that most of\ntheir suggestions have been integrated into the new paper.\nI agree with all previous reviewers and would like to add my own voice to how important the\ncontribution of this paper is towards the debate and research on the dispersal of Homo, particularly\nHomo sapiens into Asia, I think it will provide a great service to the whole palaeoanthropology and\nHuman Evolution community and move the field forward and for that alone, I would love to see the\npaper published.\nI would also like to say that I think that the comments and suggestions made by the previous\nreviewers were all valuable and in support of making this a concise and high-quality manuscript.\nI would therefore urge the authors to make sure that the suggestions are worked into the new version\nof the manuscript. Overall, this is well done, I would however ask if you could consider adding the Unit\nI label to current figure 3 in the main text as reviewer #3 requested to improve the figure. I checked\nyour suggestions of the new figure in the supplementary material and the label is missing there too. I\nneed to insist on adding this.There are a couple of other points I would like to stress further but I hope\nit is not adding too much extra work.\n• The use of the term provenance vs. providence\nI am a bit concerned about the use of the term provenance – it is sometimes not clear to me if it is\nused correctly in the paleoanthropological sense of it. Provenance in palaeoanthropology is used to\ndescribe the “history” of a fossil/artefact since its discovery – e.g., the lost fossils from Zhoukoudian\nhave a very interesting provenance from the time they were discovered until their loss, the same can\nbe said about e.g., the Le Moustier 1 Neanderthal, which was dragged all over Europe and damaged\nduring the second World war.\nOn the other hand, provenience is used to describe the exact location or place of discovery of an\nartifact (artifacts can also be soil samples) or a fossil. Given that this is a new dating paper, which\nprovides a lot of information about identifying the relevant sediment layers, it might be more\nappropriate and scientifically correct to talk about provenience rather than provenance in the paper.\n• Overall flow of the paper\nThe different parts of the paper read well but overall; the flow of the manuscript appears now a bit\ndisconnected. Perhaps this is to do with the intense review process already undertaken. Some of the\nsections do not follow well on each and changes in topic can be very abrupt. I would think the use of\nsubtitles for different sections could help with that. I would also suggest a reorganisation of some of\nthe sections to increase the flow.\nMost importantly, the order of the figures is currently not coherent and not following convention.\nI have suggested of reorganization of the three first figures and some of the sections of the main text in\nrelation to figures 4 and 5 to bring more flow into the story and to pull it all together (again). The\ncurrent version of the section titles is of course not mandatory in this form, feel free to adjust them if\nyou wish.\nI will provide these suggestions a track-changes version of the manuscript with my own additions,\nthey are also refining some of the English and add some more precision to the anatomical description\nof the skeletal remains.\nGenerally, I think the added details after the revisions for the skeletal remains is already good,\nit clearly states that the remains can be attributed to modern Homo sapiens, I have just added more\nclarification to the use of anatomical terms. I have – based on the requests from several reviewers\nand your arguments following this - made a couple of changes where you use the term “skeleton” with\ne.g., remains.\nThis is because I agree with the argument that the specimen is indeed only a partial skeleton but also\nI can see why you would argue for the “most complete” claim as there are indeed not that many\npostcranial elements for Asian fossils. Where I made the suggestions, I am just toning down the term\nmost complete/skeleton where it is not related to the argument that this is the most complete set of\nremains in East Asia/Southern China. I am glad that the authors also have highlighted the\ncombination of cranial characteristics with associated postcranial remains.\nI will also provide a cleaned-up version of the manuscript with all the changes accepted to make the\nnew suggested shape of it more visible and keeping track all the changes suggested.\nI would be very grateful if you could give these suggestions your consideration,\nKind regards,\nSandra Martelli", "reviewer_6": "Modern human skeleton fossil from the Tongtianyan Cave, Liujiang is one of the most complete H.\nsapiens skeleton fossil findings in southern China. The chronology of human fossil from this site is\nimportant for understanding the dispersal history of modern humans in East Asia. Previous\nchronological works on this site suggested an early arrival of modern human in East Asia, but these\nages were controversial. This study establishes new chronologic framework for this key site using OSL,\nU-series and radiocarbon dating, and suggest a younger age for human fossil at Liujiang in\ncorrespondence with ages of other human fossils in northern China. The human fossil at Liujiang itself\nwas dated and its provenance in the stratigraphy of the cave is assessed using a comprehensive\napproach. The paper is well-written and scientifically sound; experiments and results are robust and\nare clearly present. I think the findings of this paper will attract broad interest for readers of Nature\nCommunication. An earlier version of the manuscript has been submitted to Nature and the authors\nhave properly addressed the comments of four reviewers. Therefore, I think this manuscript is already\nof high quality, and recommend acceptance of this paper after minor revision. Some minor comments\nare listed below.\nMain text:\nLines 70-71: The chronologies of modern human remains from the Tianyuan Cave and the\nZhoukoudian Upper Cave listed here are slightly different from those listed in the abstract. According\nto Shang et al., 2007, PNAS and Li et al., 2018, JHE, bone samples from human fossil-bearing layers\nof the Tianyuan Cave and the Zhoukoudian Upper Cave were dated to 42-39 ka cal BP and 38.3-35.8\nka cal BP, respectively. Please check these literatures and use consistent numbers in the manuscript.\nLine 80: I suggest the authors cite some references here, regarding the provenance and dating of the\nLiujiang hominin fossils.\nLines 81-198: These paragraphs are very informative and I can get information regarding the\ninvestigation history of the Tongtianyan Cave, previous dating works of the cave, features of human\nfossils, geomorphologic setting and stratigraphy of the cave (and potential location of human fossils)\nby reading through these paragraphs. But to make them easier to follow, I suggest the authors may\nconsider re-order these paragraphs. Personally, I would use such a structure: 1) the location and\ngeomorphologic setting of the Tongtianyan Cave; 2) a brief investigation history of the cave; 3) the\nstratigraphy of the cave, archaeological findings of different stratigraphic units and potential location\nof human fossils; 4) features of human fossils; and 5) previous dating works and their shortage. I\nreiterate that these paragraphs are already adequately informative, so this structure issue is just a\npersonal advice.\nYou may consider swapping Figure 2 and Figure 3, as in this manuscript Figure 3 (first referred to in\nLine 163) is mentioned earlier than Figure 2 (first referred to in Line 213).\nFigure 3: There is no legend for Fig. 3b and Fig. 3c, and I can’t see the stratigraphic drawings in Figs.\n3b and 3c very clearly. The authors may consider plot Fig. 3b and Fig. 3c separately and add legends\nin the figures.\nLines 345-347: I can’t understand this sentence. Please rephrase.\nLines 355-357: Are there any other well-dated sites on this dispersal route supporting this statement?\nMethods\nLine 659: Rb is another ionising irradiation source, although typically with a low content in sediments.\nLine 661: this sentence may be changed to “the total radiation dose absorbed by mineral grains over\nthe burial time…”\nLine 684: which sample/samples was/were etched for a shorter time?\nLine 692: Reference 85 is not about OSL reader. Please check the references and make sure they are\ncited properly.\nLine 697: have you calibrated your reader using new batches of Riso calibration quartz (Batch 126 and\nonwards)? If yes, how large is the difference between the apparent machine dose rate obtained from\nthe new batch and the 108 batch? Does it validate the usage of an 8.25% correction factor?\nLines 701-702: This sentence is unclear. Do you mean the repeated regenerative dose for recycling\nratio measurement?\nLines 704-705: revise to a phrase like “…after preheat and prior to blue light stimulation” and remove\nrepetitive words “with IR stimulation carried out prior to blue stimulation”.\nLines 708-710: This sentence is not very clear, please rephrase. How long time did you use for\nOSL measurement?\nLine 713: At the end of this paragraph please clarify how did you estimate the mean De values for\nyour samples.\nLine 719-720: Do you mean 40℃ lower than preheat temperatures?\nLine 732: Finally in this paragraph, please clarify what are the final preheat and cutheat temperatures\nused for dating.\nLine 749: I guess you mean “reported by Olley et al”? And I am confused here…. In the\nsupplementary materials you say that the program by Murray et al., (2021) was used for dose rate\ncalculation; in their program, the conversion factors are derived from Guerin et al. (2011) rather than\nOlley et al. (1996). So, which conversion factors did you use exactly for dose rate estimate? Or do you\nmean you applied the conversion factors of Olley et al. (1996) for field gamma spectrometry data\nanalysis? Please clarify.\nLine 760: Reference 95 is absent in the reference list of the main text, and that reference in the\nSupplementary materials is not related to OSL dating. Please check the cited reference.\nSupplementary Materials\nLines 49-67: There are some repetitions between this paragraph and the main text. Please remove\nrepetitive sentences.\nLine 184: “Extended data Fig. 2”—I guess you mean Supplementary Fig. 2\nSupplementary Fig. 2: In figures or in the caption, please indicate which layers are these samples\nfrom. For each panel, please use different colors or line styles to differentiate samples.\nLine 438: It should be “In Steps 2 and 6”\nLine 439: response to a regenerative dose\nLine 441: remove “by”\nSupplementary Table 5, step 1: the superscript of Di should be “a,b”\nLine 443: I think here you mean “to monitor the efficacy of sensitivity change correction” or\n“to measure the recycling ratio”\nLine 461: “the preheat plateau test results…”\nLine 489: I guess you excluded aliquots with recuperation values >5%\nLine 491-502: The authors take 2D0 values as the upper dating limit for their samples. This upper\ndating limit estimate, however, is debatable as it is empirical and is based on single saturating\nexponential growth curve fitting. There is no mathematic validation that De values greater than 2D0\nmust be inaccurate—although De estimates at higher doses can be less precise due to the flatter\ngrowth curve at higher dose range, reliable De can be obtained if the shape of the growth curve can\nbe accurately established and if untruncated natural signals are properly used for De estimate (e.g.\nLi et al., 2017). If the growth curves of the samples have an additional linear or exponential component,\nthere is a potential to obtain accurate De estimates at higher doses (e.g. Murray et al., 2008; Fu et\nal., 2017), and for these growth curves the 2D0 estimate is inaccurate. The authors use 2D0 values to\nrepresent the minimum ages for three samples from Unit II. I suggest you use the real measured De\nvalues to estimate the minimum ages for these samples. Even though these De values can be\nimprecise, these real measured De values may not necessarily be wrong (but you can prudently treat\nthem as minimum De values), and they can at least provide a more useful lower bound on the true De\nvalue than the 2D0 value (see discussions of Galbraith and Roberts, 2012).\nLine 491: 2D0 represents 86% of the saturation intensity\nLine 491: “monomolecular fit”—I guess you mean “single saturating exponential growth curve fitting”\nLines 492-493: this sentence is not very clear, please rephrase\nLines 494-495: It appears to me that your aliquots have very different D0 values. As you used fine\ngrains for dating, I expect the growth curves of different aliquots should be very similar due to strong\naverage effect. Why the D0 values are so different?\nLine 499: “infinite ages”—I guess this should be “minimum ages”\nLines 503-520: Typically, the OD value and De distribution pattern are used for assessing the\ncompleteness of OSL signal resetting for single-grain OSL dating. But since this study uses fine grain\n(4-11 μm) quartz for OSL dating, the apparent OD value for each sample may not represent genuine\nbetween-grains difference in De value, as in each aliquot there can be tens of thousands of grains\ncontributing to the OSL signal so any between-grain difference in De values is averaged. This explains\nwhy you got small OD values and very concentrated De distribution for all your samples. I think for\nfine grain dating the OD value and De distribution pattern provide little useful information about signal\nresetting, but the De (t) plots, as provided by the authors in their rebuttal letter to the reviewers of\nNature, can provide evidence that the OSL signals are sufficiently bleached, and the consistency\nbetween OSL ages and radiocarbon ages also suggest good signal bleaching. The authors may\nconsider adding the De (t) plots (R-Fig.2) into the Supplementary Information.\nLine 524-548: For samples exhibiting U-series disequilibrium, it would be better to estimate the\nimpact of U-series disequilibrium on dose rate quantitatively, if possible.\nSupplementary Fig. 13: It would be great if you could indicate which sample is from with unit/layer in\nthis figure.\nSupplementary Table 7 and Table 8: The errors of OSL ages present in Supplementary Table 7\n(given as 1σ error) and Supplementary Table 8 (given as 2σ error) are the same, so I guess these\nerrors are random-only errors (if the authors use random-only errors in the Bayesian age model).\nIt would be great if the authors could provide random plus systematic error for each age in\nSupplementary Table 7, which would represent full uncertainty for each age estimate.\nReferences\nFu, X., Cohen, T.J., Arnold, L.J., 2017. Extending the record of lacustrine phases beyond the last\ninterglacial for Lake Eyre in central Australia using luminescence dating. Quaternary Science Reviews\n162, 88–110.\nGalbraith, R.F., Roberts, R.G., 2012. Statistical aspects of equivalent dose and error calculation and\ndisplay in OSL dating: An overview and some recommendations. Quaternary Geochronology 11, 1–27.\nGuérin, G., Mercier, N., Adamiec, G., 2011. Dose rate conversion factors: update. Ancient TL 29 (1),\n5–8.\nLi, B., Jacobs, Z., Roberts, R.G., Galbraith, R., Peng, J., 2017. Variability in quartz OSL signals caused\nby measurement uncertainties: Problems and solutions. Quaternary Geochronology 41, 11–25.\nLi, F., Bae, C.J., Ramsey, C.B., Chen, F., Gao, X., 2018. Re-dating Zhoukoudian Upper Cave, northern\nChina and its regional significance. Journal of Human Evolution 121, 170–177.\nMurray, A., Arnold, L.J., Buylaert, J.-P., Guérin, G., Qin, J., Singhvi, A.K., Smedley, R., Thomsen, K.J.,\n2021. Optically stimulated luminescence dating using quartz. Nat Rev Methods Primers 1, 1–31.\nMurray, A., Buylaert, J.-P., Henriksen, M., Svendsen, J.-I., Mangerud, J., 2008. Testing the reliability\nof quartz OSL ages beyond the Eemian. Radiation Measurements 43, 776–780.\nOlley, J.M., Murray, A., Roberts, R.G., 1996. The effects of disequilibria in the uranium and thorium\ndecay chains on burial dose rates in fluvial sediments. Quaternary Science Reviews 15, 751–760.\nShang, H., Tong, H., Zhang, S., Chen, F., Trinkaus, E., 2007. An early modern human from Tianyuan\nCave, Zhoukoudian, China. Proc Natl Acad Sci 104, 6573–6578.", "reviewer_author_response": "Responses to Reviewers’ Comments\nWe appreciate reviewers’ constructive comments and suggestions on the previous version of\nour manuscript, which have been addressed point-by-point as follows.\nREVIEWER COMMENTS\nReferee #2:\nNew Late Pleistocene Age for the Homo sapiens skeleton from Liujiang, southern China\nThe new dating of the skeletal remains from Liujiang cave is a useful addition to our knowledge\nof the history of H. sapiens in China. The account of the dating is detailed, thorough and\nconvincing, and should end any controversy over the age of this material. The description of\nthe skeletal evidence is also useful and provides a more up-to-date overview of its coverage in\nthe Wu and Poirier 1995 volume Human Evolution in China (Oxford 1995).\nAR: We thank the reviewer for the positive evaluation of our manuscript. We appreciate the\ncomment that the paper was “detailed, thorough and convincing” and we are pleased to see that\nthe reviewer believes that our new dating program has ended the controversy surrounding the\nLiujiang skeletal remains. Moreover, we appreciate that the reviewer finds our skeletal\ndescriptions to be a useful addition to the literature on important Chinese fossils.\nRegarding publication in Nature, my main concern is that Liujiang has now lost its international\nsignificance. Its new dating at 33-24 ka brings the skeleton in line with other East Asian finds,\nsuch as Salkhit, (Mongolia), Upper Cave, Zhoukoudian, Moh Thiew (Thailand); and shows that\nit is younger than the specimens from Tianyuandong, North China, Niah Cave, Borneo and Tam\nPa Ling, Laos, all of which are >40 Ka. As a result of the re-dating, Liujiang is now in the\ncategory of “interesting but not very important” in international terms. I therefore think it is\ninappropriate for Nature. There is no doubt that this is an excellent paper; however, it is one\nthat has a regional but not international significance.\nThe redating and skeletal descriptions are certainly worth publication in a journal such as\nJournal of Human Evolution, where the new evidence can be read by the relatively small\ncommunity familiar with the human skeletal record of China and SE Asia.\nAR: We appreciate the positive statements by the reviewer about our paper and the importance\nof the Liujiang skeletal material. However, we respectfully disagree with the reviewer that the\nfossil material has “lost its international significance” and now not appropriate for Nature.\nWe would like to emphasize that Liujiang is one of the most recognized fossils of a modern\nhuman in Eastern Asia, which has been widely cited and studied. As a representative of ‘early’\nmodern humans in East Asia, Liujiang has gained international significance, serving as\nimportant material for understanding the dispersal of modern humans across Eurasia.\nOur re-dating of the site stratigraphy and skeleton is one of the most advanced studies of its\nkind in China and all of Asia. The origin and dispersal of Homo sapiens in Asia has been the\n1\nsubject of major debates, and much of the problem about the timing of migrations has been the\nlack of dating, including direct dating, on fossil material. We not only show that the Liujiang\nskeleton is young, and not representative of early Homo sapiens populations, but we also show\nscholars across the world that the methods that we apply are necessary to establish accurate\ndating. This has major implications for theories about human origins and dispersals.\nEven though Liujiang is younger than anticipated, the reviewer is correct that it now forms a\nkey fossil to demonstrate the wider occupation of Eastern Asia in the later Pleistocene, i.e, after\nca. 40 ka. The fossil skeleton at Liujiang is a rare find and it now provides important new\ninformation on human demography in this critical time period.\nDear Authors,\nThank you for the opportunity to read your manuscript NCOMMS-23-34915-T “New Late\nPleistocene Age for the Homo sapiens skeleton from Liujiang, southern China. I have been\ninvited to share my thoughts on a broader level for the manuscript, which I am doing in the\nfollowing, I will not comment much on individual items raised by your four other excellent\nreviewers. I am glad to see that most of their suggestions have been integrated into the new\npaper.\nAR: We thank the reviewer for pointing out that the suggestions of the reviewers has been well\nintegrated into our revised paper.\nI agree with all previous reviewers and would like to add my own voice to how important the\ncontribution of this paper is towards the debate and research on the dispersal of Homo,\nparticularly Homo sapiens into Asia, I think it will provide a great service to the whole\npalaeoanthropology and Human Evolution community and move the field forward and for that\nalone, I would love to see the paper published.\nAR: We appreciate this comment about the importance of the Liujiang skeleton (in\ncontradiction to the points raised by Reviewer #2).\nI would also like to say that I think that the comments and suggestions made by the previous\nreviewers were all valuable and in support of making this a concise and high-quality manuscript.\nI would therefore urge the authors to make sure that the suggestions are worked into the new\nversion of the manuscript. Overall, this is well done, I would however ask if you could consider\nadding the Unit I label to current figure 3 in the main text as reviewer #3 requested to improve\nthe figure. I checked your suggestions of the new figure in the supplementary material and the\nlabel is missing there too. I need to insist on adding this. There are a couple of other points I\nwould like to stress further but I hope it is not adding too much extra work.\nAR: In our revised manuscript, Unit I was added in MAIN TEXT Fig. 2 and Supplementary\nFig.1. As this sedimentary unit is beneath Unit III and Unit II, and is not exposed in this section,\nbut only exposed on its contrary side of this section, the upper boundary of which thus is only\npresented in a dashed line (Fig. 2 and Supplementary Fig.1a).\n• The use of the term provenance vs. providence\nI am a bit concerned about the use of the term provenance – it is sometimes not clear to me if\nit is used correctly in the paleoanthropological sense of it. Provenance in palaeoanthropology\nis used to describe the “history” of a fossil/artefact since its discovery – e.g., the lost fossils\nfrom Zhoukoudian have a very interesting provenance from the time they were discovered until\ntheir loss, the same can be said about e.g., the Le Moustier 1 Neanderthal, which was dragged\nall over Europe and damaged during the second World war.\nOn the other hand, provenience is used to describe the exact location or place of discovery of\n3\nan artifact (artifacts can also be soil samples) or a fossil. Given that this is a new dating paper,\nwhich provides a lot of information about identifying the relevant sediment layers, it might be\nmore appropriate and scientifically correct to talk about provenience rather than provenance in\nthe paper.\nAR: Thank you for your suggestion. In our revised manuscript, we replaced “provenance” with\nthe term “provenience” (Main text Lines 48, 79, 162 …).\n• Overall flow of the paper\nThe different parts of the paper read well but overall; the flow of the manuscript appears now a\nbit disconnected. Perhaps this is to do with the intense review process already undertaken. Some\nof the sections do not follow well on each and changes in topic can be very abrupt. I would\nthink the use of subtitles for different sections could help with that. I would also suggest a\nreorganisation of some of the sections to increase the flow.\nAR: Thank you for your suggestion. In our revised manuscript, subtitles were used for each\nsection according to your suggestion. We also rearranged some descriptions in our revised\nmanuscript to improve the flow (Main text Lines 60, 175, 206, 243, 338).\nMost importantly, the order of the figures is currently not coherent and not following convention.\nI have suggested of reorganization of the three first figures and some of the sections of the main\ntext in relation to figures 4 and 5 to bring more flow into the story and to pull it all together\n(again). The current version of the section titles is of course not mandatory in this form, feel\nfree to adjust them if you wish.\nI will provide these suggestions a track-changes version of the manuscript with my own\nadditions, they are also refining some of the English and add some more precision to the\nanatomical description of the skeletal remains.\nAR: Thank you for your suggestion. To improve the flow of the paper, Figure 2 and Figure 3\nhave been swapped in the revised main text (which is also suggested by Referee #6), and their\ncaptions have also been exchanged. In addition, we moved Fig. 4b&c into Fig. 5, as Fig. 4b&c\nis mentioned after Fig. 5. The order of the figures is now coherent and follows convention.\nGenerally, I think the added details after the revisions for the skeletal remains is already good,\nit clearly states that the remains can be attributed to modern Homo sapiens, I have just added\nmore clarification to the use of anatomical terms. I have – based on the requests from several\nreviewers and your arguments following this - made a couple of changes where you use the\nterm “skeleton” with e.g., remains.\nThis is because I agree with the argument that the specimen is indeed only a partial skeleton\nbut also I can see why you would argue for the “most complete” claim as there are indeed not\nthat many postcranial elements for Asian fossils. Where I made the suggestions, I am just\ntoning down the term most complete/skeleton where it is not related to the argument that this is\nthe most complete set of remains in East Asia/Southern China. I am glad that the authors also\nhave highlighted the combination of cranial characteristics with associated postcranial remains.\nthe new suggested shape of it more visible and keeping track all the changes suggested.\nAR: We appreciate the suggestions for revision, and we made the revisions accordingly. We\nagree that the “most complete” is not the best term to describe the skeletal remains; therefore,\nwe made a title change and toned down the “most complete/skeleton”. We state that Liujiang is\nthe best-preserved late Pleistocene human fossil in East Asia/Southern China, in agreement with\nthe recommendations here.\nModern human skeleton fossil from the Tongtianyan Cave, Liujiang is one of the most complete\nH. sapiens skeleton fossil findings in southern China. The chronology of human fossil from this\nsite is important for understanding the dispersal history of modern humans in East Asia.\nPrevious chronological works on this site suggested an early arrival of modern human in East\nAsia, but these ages were controversial. This study establishes new chronologic framework for\nthis key site using OSL, U-series and radiocarbon dating, and suggest a younger age for human\nfossil at Liujiang in correspondence with ages of other human fossils in northern China. The\nhuman fossil at Liujiang itself was dated and its provenance in the stratigraphy of the cave is\nassessed using a comprehensive approach. The paper is well-written and scientifically sound;\nexperiments and results are robust and are clearly present. I think the findings of this paper will\nattract broad interest for readers of Nature Communication. An earlier version of the manuscript\nhas been submitted to Nature and the authors have properly addressed the comments of four\nreviewers. Therefore, I think this manuscript is already of high quality, and recommend\nacceptance of this paper after minor revision. Some minor comments are listed below.\nAR: We appreciate the series of positive comments by Reviewer #6 and we are pleased that\nthey value the scientific approach taken in our manuscript. Again, this reviewer points out the\ninternational significance of Liujiang human fossils, in conflict with the views of Reviewer #2.\nMain text:\nReviewer’s comment 1 (RC): Lines 70-71: The chronologies of modern human remains from\nthe Tianyuan Cave and the Zhoukoudian Upper Cave listed here are slightly different from\nthose listed in the abstract. According to Shang et al., 2007, PNAS and Li et al., 2018, JHE,\nbone samples from human fossil-bearing layers of the Tianyuan Cave and the Zhoukoudian\nUpper Cave were dated to 42-39 ka cal BP and 38.3-35.8 ka cal BP, respectively. Please check\nthese literatures and use consistent numbers in the manuscript.\nAR: Done. The 14C ages of the human remains from the Tianyuan Cave and the Zhoukoudian\nupper Cave were updated in our revised text. These 14C ages have also been re-calibrated based\non the INTALCAL 20 curves as requested by the Nature referees. This is why the age cited was\ndifferent from the published dates.\nLine 80: I suggest the authors cite some references here, regarding the provenance and dating\nof the Liujiang hominin fossils.\nAR: Done. References have now been cited (Main text Line 80).\nLines 81-198: These paragraphs are very informative and I can get information regarding the\ninvestigation history of the Tongtianyan Cave, previous dating works of the cave, features of\nhuman fossils, geomorphologic setting and stratigraphy of the cave (and potential location of\nhuman fossils) by reading through these paragraphs. But to make them easier to follow, I\nsuggest the authors may consider re-order these paragraphs. Personally, I would use such a\nstructure: 1) the location and geomorphologic setting of the Tongtianyan Cave; 2) a brief\n6\ninvestigation history of the cave; 3) the stratigraphy of the cave, archaeological findings of\ndifferent stratigraphic units and potential location of human fossils; 4) features of human fossils;\nand 5) previous dating works and their shortage. I reiterate that these paragraphs are already\nadequately informative, so this structure issue is just a personal advice.\nAR: Thank you very much for your suggestions. In our revised manuscript, these paragraphs\nhave been reorganized. To take full account of the comments and suggestions of the referee,\nsome section titles were added, improving the flow and content of our manuscript (Main text\nLines 60, 155-174, 175, 206, 243, 338).\nYou may consider swapping Figure 2 and Figure 3, as in this manuscript Figure 3 (first referred\nto in Line 163) is mentioned earlier than Figure 2 (first referred to in Line 213).\nAR: Done. The order and title of the two figures have been changed (Main text Lines 199-204\n& 236-241).\nFigure 3: There is no legend for Fig. 3b and Fig. 3c, and I can’t see the stratigraphic drawings\nin Figs. 3b and 3c very clearly. The authors may consider plot Fig. 3b and Fig. 3c separately\nand add legends in the figures.\nAR: Done. Legends for the Fig.3b and Fig.3c were revised (Fig.2b & 2c, Main text Line 199).\nLines 345-347: I can’t understand this sentence. Please rephrase.\nAR: Done. It has been rephrased (Main text Lines 357-359).\nLines 355-357: Are there any other well-dated sites on this dispersal route supporting this\nstatement?\nAR: Here we propose a possible rapid dispersal across Eurasia around 30 ka based on the\nsimilarity of cranial shape between Liujiang and Cro-Magnon. Owing to the scarcity of well-\npreserved human skulls with similar chronologies, we still cannot determine how the dispersal\nhappened, as it may have taken place along the “southern route” via India, or the “northern\nroute” across the Central Asia. As more and more human fossils would be discovered in the\nfuture, this dispersal may be better documented. We provide a more cautious statement: “The\nrevised age estimate for Liujiang corresponds with well-known fossil at Cro-Magnon (France,\n31-33 ka)34. In addition to chronological contemporaneity, the close affinity of cranial shape\nbetween Liujiang and Cro-Magnon 1 from Western Europe17,28 imply little morphological\ndifferentiation among modern human populations in Europe and East Asia, or rapid dispersal\nevents of early modern humans across Eurasia continent around ~30 ka” (Main text Lines 368-\n373).\nMethods\nLine 659: Rb is another ionising irradiation source, although typically with a low content in\nsediments.\nAR: This is a good pint. The sentence was revised: “The luminescence emitted from minerals\n(e.g., quartz and feldspar) under artificial light exposure is proportional to the absorbed energy\naccumulated within the crystal lattice of minerals by ionizing radiation (e.g., alpha, beta or\ngamma radiation) from radioactive elements such as uranium (U), thorium (Th), Rubidium (Rb)\n7\nand potassium (K) in the environment, as well as cosmic rays” (Main text Lines 714-719).\nLine 661: this sentence may be changed to “the total radiation dose absorbed by mineral grains\nover the burial time…”\nAR: Thank you for the suggestion. This sentence been changed accordingly (Main text Lines\n719-721).\nLine 684: which sample/samples was/were etched for a shorter time?\nAR: Done. The samples with less-time etching have been clarified (Main text Lines 743-746).\nLine 692: Reference 85 is not about OSL reader. Please check the references and make sure\nthey are cited properly.\nAR: Done. It has been corrected (Main text Line 753).\nLine 697: have you calibrated your reader using new batches of Riso calibration quartz (Batch\n126 and onwards)? If yes, how large is the difference between the apparent machine dose rate\nobtained from the new batch and the 108 batch? Does it validate the usage of an 8.25%\ncorrection factor?\nAR: We have re-calibrated our reader using the new batch of RISO calibration quartz (batch\n126 of 6.00 Gy) as required by the Nature reviewer and found an underestimation around 8.2%.\nConsidering the possible measurement error, we corrected our previous results using a\ncorrection factor of 8.25% as suggested by Autzen et al. (2022).\nLines 701-702: This sentence is unclear. Do you mean the repeated regenerative dose for\nrecycling ratio measurement?\nAR: Done. The sentence has been rephrased: “After the standard SAR protocol, a repeated\nregenerative dose measurement was applied to detect the recycling ratio measurement”. (Main\ntext Lines 761-763)\nLines 704-705: revise to a phrase like “…after preheat and prior to blue light stimulation” and\nremove repetitive words “with IR stimulation carried out prior to blue stimulation”.\nAR: Done. The sentence has been revised: “In addition, to test the purity of the quartz extracts,\nan additional recycling step was given at last to each aliquot, in which IR stimulation of grains\nfor 40 s at room temperature using infrared LEDs was set after preheat and prior to blue light\nstimulation” (Lines 763-766)\nLines 708-710: This sentence is not very clear, please rephrase. How long time did you use for\nOSL measurement?\nAR: Done. This has been rephrased: “These measured aliquots having the recycling ratio or\nOSL IR depletion ratio exceeding the acceptable range (0.9-1.1), or with the recuperation over\n5%, were excluded from the D determination”. (Main text Lines 768-771)\ne\nLine 713: At the end of this paragraph please clarify how did you estimate the mean De values\nfor your samples.\ne\nthe arithmetic mean was used for D calculation of each sample”. (Main text Lines 773-774)\ne\nLines 719-720: Do you mean 40℃ lower than preheat temperatures?\nAR: Yes. The cut-heat temperature was set to be 40 °C lower than preheat temperatures. In our\nrevision, the sentence has been changed: “…with the cut-heat ranged from 160 °C to 260 °C at\n20 °C increments basically tracking and lagging the preheat temperatures by a margin of 40 °C”.\n(Main text Lines 778-782)\nLine 732: Finally in this paragraph, please clarify what are the final preheat and cutheat\ntemperatures used for dating.\nAR: Done. A sentence was added: “Finally, a preheat temperature of 260 °C and a cut-heat at\n220 °C were used for D determination of all samples.” (Main text Lines 793-794)\ne\nLine 749: I guess you mean “reported by Olley et al”? And I am confused here…. In the\nsupplementary materials you say that the program by Murray et al., (2021) was used for dose\nrate calculation; in their program, the conversion factors are derived from Guerin et al. (2011)\nrather than Olley et al. (1996). So, which conversion factors did you use exactly for dose rate\nestimate? Or do you mean you applied the conversion factors of Olley et al. (1996) for field\ngamma spectrometry data analysis? Please clarify.\nAR: Yes. It has been re-clarified: “Each sample was measured for 8 hours in the field. Spectral\ndata were converted to activity concentrations and infinite matrix dose rates using conversion\ndata by Guerin et al.85” (Main text Line 809-811)\nLine 760: Reference 95 is absent in the reference list of the main text, and that reference in the\nSupplementary materials is not related to OSL dating. Please check the cited reference.\nAR: Done. The reference has been replaced with “Bøtter-Jensen, L., et al. Developments in\nradiation, stimulation and observation facilities in luminescence measurements. Radiation\nMeasurements 51, 1023-1045 (2003)”.\nSupplementary Materials\nLines 49-67: There are some repetitions between this paragraph and the main text. Please\nremove repetitive sentences.\nAR: Done. The repetitive sentences have been removed from the Supplementary Information.\nLine 184: “Extended data Fig. 2”—I guess you mean Supplementary Fig. 2\nAR: Done. It has been changed as “Supplementary Fig.2”. (Supplementary Information Line\n167)\nSupplementary Fig. 2: In figures or in the caption, please indicate which layers are these\nsamples from. For each panel, please use different colors or line styles to differentiate samples.\nAR: Done. In the caption of Supplementary Fig.2, the information about the location of these\nsamples are addressed as follows: “Samples of HED-640, HED-641, HED-628 and 21LJ_16\nare from Layer 2, HED-627, HED-642, 21LJ_12, 21LJ_14 and 21LJ_15 are from Layer 3,\nof HED-626, HED-638, HED-639, LJ_13, LJ_17 and LJ_20 are collected from Unit II.”\n(Supplementary Information Lines 198-202)\nLine 438: It should be “In Steps 2 and 6”\nAR: Done. It has been changed to “In Steps 2 and 6”. (Supplementary Information Line 426)\nLine 439: response to a regenerative dose\nAR: Done. It has been revised. (Supplementary Information Line 427)\nLine 441: remove “by”\nAR: Done. It has been removed in our revised text. (Supplementary Information Line 429)\nSupplementary Table 5, step 1: the superscript of Di should be “a,b”\nAR: Done. It has been revised to “a, b” (Supplementary Table 5).\nLine 443: I think here you mean “to monitor the efficacy of sensitivity change correction” or\n“to measure the recycling ratio”\nAR: Done. The sentence has been revised into “Repeated dose was given at last to monitor the\nefficiency of sensitivity change correction”.\nLine 461: “the preheat plateau test results…”\nAR: Done. It has been revised. (Supplementary Information Line 452)\nLine 489: I guess you excluded aliquots with recuperation values >5%\nAR: Done. It has been revised to “>5%”. (Supplementary Information Line 480)\nLine 491-502: The authors take 2D0 values as the upper dating limit for their samples. This\nupper dating limit estimate, however, is debatable as it is empirical and is based on single\nsaturating exponential growth curve fitting. There is no mathematic validation that De values\ngreater than 2D0 must be inaccurate—although De estimates at higher doses can be less precise\ndue to the flatter growth curve at higher dose range, reliable De can be obtained if the shape of\nthe growth curve can be accurately established and if untruncated natural signals are properly\nused for De estimate (e.g. Li et al., 2017). If the growth curves of the samples have an additional\nlinear or exponential component, there is a potential to obtain accurate De estimates at higher\ndoses (e.g. Murray et al., 2008; Fu et al., 2017), and for these growth curves the 2D0 estimate\nis inaccurate. The authors use 2D0 values to represent the minimum ages for three samples\nfrom Unit II. I suggest you use the real measured De values to estimate the minimum ages for\nthese samples. Even though these De values can be imprecise, these real measured De values\nmay not necessarily be wrong (but you can prudently treat them as minimum De values), and\nthey can at least provide a more useful lower bound on the true De value than the 2D0 value\n(see discussions of Galbraith and Roberts, 2012).\nAR: Thank you for the suggestions. In our revised manuscript, we recalculated the De values\nfor these three samples from the Unit II by fitting their regeneration data with the sum of an\n10\nexponential and a linear component and subsequently calculated the corresponding ages. In our\nrevised manuscript, some clarifications about our new fitting methods were made as follows:\n“Some studies suggested that reliable D can be obtained when the shape of the growth curve\ne\ncan be accurately established and the untruncated natural signals are properly used for D\ne\nestimate110, and it has also been proved that accurate D estimates at higher doses111-114 can\ne\nactually be obtained by a by a function which is the sum of a single saturating exponential and\nlinear component or by the sum of two saturating exponentials when the growth curves of the\nsamples have an additional linear or exponential components. Thereafter, the data for these\nthree samples, thereafter, were fitted with the sum of an exponential and a linear component,\nwhich seem to aligns with the regeneration data points better.” (Supplementary Information\nLines 488-499)\nSome discussion about the results of these samples from Unit II are also made in our revised\ntext as follows: “However, the three samples from the Unit-II beneath the thick flowstone layer\n(FL-2) generate the ages of 62±4 ka, 103±7 ka and 151±12 ka, respectively, which are much\nolder than the samples from Unit III. Actually, the samples HED-626 and HED-638 are\ncollected between the flowstone Layer FL-2 and Layer FL-3, which were dated to 71±5 ka and\n133±11 ka by carbonate U-series dating method, respectively. While the sample HED-639 are\ntaken from the layer under FL-3 but above the flowstone Layer FL-4 which have an age of\n240±37 ka. It can be seen that these ages agree with our as well as previously published U-Th\ndating results on these flowstone layers 3, even considering the possible age underestimation\ndue to the U-series disequilibrium U-series disequilibrium in this unit.” (Supplementary\nInformation Lines 594-604)\nLine 491: 2D0 represents 86% of the saturation intensity\nAR: Done. It has been clarified in our revised text: “2D0 (86% of the saturation intensity for a\nsingle saturating exponential growth curve fitting) values is generally taken as the practical\nupper limit for dose estimation”. (Supplementary Information Line 482)\nLine 491: “monomolecular fit”—I guess you mean “single saturating exponential growth curve\nfitting”\nAR: Done. It has been revised. (Supplementary Information Line 482)\nLines 492-493: this sentence is not very clear, please rephrase\nAR: Done. We rephrased the sentence: “2D0 (86% of the saturation intensity for a single\nsaturating exponential growth curve fitting) values is generally taken as the practical upper limit\nfor dose estimation80 to evaluated whether the OSL signals for each measured aliquot is\nsaturated or not, and the aliquots with De values higher than which was mostly used to calculate\nminimum ages.” (Supplementary Information Lines 482-486)\nLines 494-495: It appears to me that your aliquots have very different D0 values. As you used\nfine grains for dating, I expect the growth curves of different aliquots should be very similar\ndue to strong average effect. Why the D0 values are so different?\nAR: The growth curves of different aliquots for these three samples from Unit-II are rather\nsimilar, as shown by the standard growth curves after least square-normalisation yielded by the\n11\nregeneration data of samples HED-626, HED-638 and HED-639. In our revised text, we\nremoved the sentence and rephrased the sentences as follows: “2D (86% of the saturation\n0\nintensity for a single saturating exponential growth curve fitting) values is generally taken as\nthe practical upper limit for dose estimation80 to evaluated whether the OSL signals for each\nmeasured aliquot is saturated or not, and the aliquots with D values higher than which was\ne\nmostly used to calculate minimum ages.” (Supplementary Information Lines 482-486)\nR-Fig.1 The standard growth curves (SGC) after least square-normalisation yielded by these\nregeneration data for the samples HED-626, HED-638 and HED-639.\nLine 499: “infinite ages”—I guess this should be “minimum ages”\nAR: Done. It has been changed to “minimum ages”. (Supplementary Information Line 485-486)\nLines 503-520: Typically, the OD value and De distribution pattern are used for assessing the\ncompleteness of OSL signal resetting for single-grain OSL dating. But since this study uses fine\ngrain (4-11 μm) quartz for OSL dating, the apparent OD value for each sample may not\nrepresent genuine between-grains difference in De value, as in each aliquot there can be tens of\nthousands of grains contributing to the OSL signal so any between-grain difference in De values\nis averaged. This explains why you got small OD values and very concentrated De distribution\nfor all your samples. I think for fine grain dating the OD value and De distribution pattern\nprovide little useful information about signal resetting, but the De (t) plots, as provided by the\nauthors in their rebuttal letter to the reviewers of Nature, can provide evidence that the OSL\nsignals are sufficiently bleached, and the consistency between OSL ages and radiocarbon ages\nalso suggest good signal bleaching. The authors may consider adding the De (t) plots (R-Fig.2)\ninto the Supplementary Information.\nAR: Thank you for these constructive suggestions. It is correct that the OD value and D\ne\ndistribution pattern make more sense for evaluating the completeness of OSL signal resetting\nfor single-grain OSL dating rather than fine-grain quartz OSL dating. However, in this study, it\nis used to provide one part of our evidence for good signal resetting of the fine-grain quartz.\nBesides, the sedimentary processes, and the D (t) plots also provide some other supports for\ne\nour conclusion. Based on your comments, we included the D (t) plots in the Supplementary\ne\nissues. We rephrased the paragraph as the follows: “Incomplete resetting is an issue for OSL\ndating. However, signal bleaching seems not to be a problem for the samples from Tongtianyan\ncave, for the following reasons: (1) The sediments in Layers 2 and 3 are mainly dominated by\nhomogeneous silty clay, suggesting that they may have been extensively weathered and\ntransported into the cave by low-energy slope sheet flow rather than by flood-like water current.\nGiven that the quartz mineral can be bleached in a few minutes, and the luminescence signals\nof quartz grains are dominated by the fast component, it therefore seems that these quartz grains\nmay have experienced full exposure to sunlight. Afterwards, owning to the sloping ground\nsurface toward the deep cave in the passage connecting the cave entrance with the chamber\nwhere the sediments accumulated, with a dip angle of ~10°, the sediments entering the cave\ncan be transported smoothly to the deep chamber and trapped there without disturbance. As the\ndeep cave where the sediments deposited is absolutely in darkness, there is no chance for\nresetting of the OSL signal for them, the burial age of the human fossils seems to be close to\nthat of the resetting time of the luminescence signals outside the cave. (2) All (unsaturated)\nsamples from the Unit-II in Tongtianyan cave typically describe a normal Gaussian distribution\nof De values, with only a few samples slightly skewed (Supplementary Fig. 12), and all give\nover-dispersion (σOD) values representing the relative standard deviation of the D distribution\ne\nof <20%, indicating that these sample may have been well bleached prior to deposition115,116.\n(3) D as a function of illumination time (D (t)), is also used to identify the partial resetting of\ne e\nquartz OSL signals117. As shown in the D (t) plots (Supplementary Fig.13), all of the eight\ne\nunsaturated samples yielded consistent D (t) values at the 1ϭ confidence level independent of\ne\nsignal integration, which also well suggests full resetting of the fast and medium components\nprior to deposition117. In addition, the consistency between OSL ages and radiocarbon ages in\nthe same layer also provides additional support for the conclusion that there is good OSL signal\nbleaching for the quartz from Tongtianyan cave.” (Supplementary Information Lines 500-526)\nLine 524-548: For samples exhibiting U-series disequilibrium, it would be better to estimate\nthe impact of U-series disequilibrium on dose rate quantitatively, if possible.\nAR: Done. In our revised manuscript the possible impact of U-series disequilibrium on dose\nrate and ages for the three sample from the Unit II were evaluated and are clarified as follows:\n“These additional 238U resulted from the downward leaching carbonate may have led to an\noverestimation of the total dose rate for the three sample HED-626, HED-638 and HED-6329\nfrom the Unit II by 0.27±0.27 Gy/ka, 0.94±0.36 Gy/ka and 0.55±0.26 Gy/ka in maximum,\nrespectively, and thus caused an age underestimation of 4±4%, 18±8% and 15±8%,\nrespectively.” (Supplementary Information Lines 556-560)\nSupplementary Fig. 13: It would be great if you could indicate which sample is from with\nunit/layer in this figure.\nAR: Thanks for the suggestion. We added the Unit/Layer name for each sample in our revised\nfigure (Supplementary Fig. 14)\nSupplementary Table 7 and Table 8: The errors of OSL ages present in Supplementary Table 7\n(given as 1σ error) and Supplementary Table 8 (given as 2σ error) are the same, so I guess these\n13\nerrors are random-only errors (if the authors use random-only errors in the Bayesian age model).\nIt would be great if the authors could provide random plus systematic error for each age in\nSupplementary Table 7, which would represent full uncertainty for each age estimate.\nAR: The age errors presented in Supplementary Table 7 represent full uncertainties in their age\nestimations. Except for the random-only errors, these age uncertainties for them also include\nnot only the systematic error yielded during the measurements of radionuclides concentrations\nand associated dose rate calculations, but also a 2.1% systematic error to allow covering any\nbias associated with calibration of the laboratory beta source.\nIn our Bayesian modelling using the Oxcal online program, not only the OSL ages but also the\nradiocarbon and U-series dates were used. Since the radiocarbon and U-series dating data both\ncontain independent systematic errors and share systematic errors with each other, it is thus\nnecessary to consider not only random errors but also systematic errors in our models. Our\nresults actually show an overall A indices value of 113.7, suggesting that there is no sign of any\nsignificant systematic error in the OSL age estimates (Rhodes et al., 2003), which also provide\nsome supports for our conclusions.\nCited References\nAutzen et al., “Calibration quartz: An update on dose calculations for luminescence dating”,\nRadiation Measurements 157, 106828, 2022\nRhodes, E., Ramsey, C.B., Outram, Z., Batt, C., Willis, L., Dockrill, S., Bond, J., 2003.\nBayesian methods applied to the interpretation of multiple OSL dates: high precision sediment\nages from Old Scatness Broch excavations, Shetland Isles. Quaternary Science Reviews 22,\n1231-1244.\n14"}, "author_response": ""}, {"round": 2, "reviewer_comments": {"reviewer_2": "Reviewers' Comments:\nReviewer #2:\nRemarks to the Author:\nMy opinion of this paper is unchanged from the last time I reviewed it. Although it is an excellent piece\nof research that clearly establishes the age of the Liujiang partial skeleton as between ~33 and 24 ka,\nI still maintain that it is not appropriate for Nature. This is because Nature’s reputation stands in\npublishing material that is game-changing, ground-breaking and clearly of international significance.\nUnfortunately, the reporting of another H. sapiens skeleton from East Asia that is ~33-24 ka in age is\nno longer in that category – there are already older examples such as Tanyuandong and Upper Cave\nin China, and Salkhit in Mongolia, as well as various other earlier examples from SE Asia such as Niah\nand Lida Ajer. Additionally, if the Luijiang remains are as young as 24 ka, they are even less\nsignificant internationally.\nLiujiang was only important because earlier – and now shown to be erroneous – estimates of its age\nas early Upper or even late Middle Pleistocene helped fuel arguments for a multi-regional model of\nhuman evolution. Even before the re-dating of Liujiang, that model had been almost wholly\nabandoned in favour of an African origin of H. sapiens. With the new dating of Liujiang, it is now in the\ncategory of an interesting but not very significant discovery at an international level.\nAs I suggested previously, the redating and skeletal descriptions are certainly worth publication in a\njournal such as Journal of Human Evolution, where the new evidence can be read by the relatively\nsmall community familiar with the human skeletal record of China and SE Asia.", "reviewer_5": "Reviewer #5:\nRemarks to the Author:\nDear Authors,\nThank you very much for your detailed response to my suggestions and clear layout of the steps you\ntook to integrate the suggestions into your manuscript.\nI think the manuscript does flow better now and the message/story of the work is clear and I am\nhappy to recommend it ready for publication.\nI noticed these spelling errors, I am sure they can be fixed quickly:\nPage 6 line 150 mongloid, should be mongoloid?\nPage 17 line 384 pyriform aperture should be piriform aperture", "reviewer_6": "Reviewer #6:\nRemarks to the Author:\nThe authors have addressed all my comments properly. I am happy to support publishing this paper in\nNature Communication.\nJust a few minor points to be corrected:\n-Line 744 in the main text: “except for some a sample” should be revised to “except for some\nsamples”.\n-Line 763 in the main text: “to detect the recycling ratio measurement” may be revised to “to\ndetermine the recycling ratio”\n- reference #111 in the supplementary materials is not about luminescence dating. Please cite the\nright reference.", "reviewer_author_response": "Responses to Reviewers’ Comments\nWe appreciate the editor’s and reviewers’ constructive comments and suggestions on the\nprevious version of our manuscript, which have been addressed point-by-point as follows.\nReviewer #2 (Remarks to the Author):\nMy opinion of this paper is unchanged from the last time I reviewed it. Although it is\nan excellent piece of research that clearly establishes the age of the Liujiang partial\nskeleton as between ~33 and 24 ka, I still maintain that it is not appropriate for Nature.\nThis is because Nature’s reputation stands in publishing material that is game-changing,\nground-breaking and clearly of international significance. Unfortunately, the reporting\nof another H. sapiens skeleton from East Asia that is ~33-24 ka in age is no longer in\nthat category – there are already older examples such as Tanyuandong and Upper Cave\nin China, and Salkhit in Mongolia, as well as various other earlier examples from SE\nAsia such as Niah and Lida Ajer. Additionally, if the Luijiang remains are as young as\n24 ka, they are even less significant internationally.\nLiujiang was only important because earlier – and now shown to be erroneous –\nestimates of its age as early Upper or even late Middle Pleistocene helped fuel\narguments for a multi-regional model of human evolution. Even before the re-dating of\nLiujiang, that model had been almost wholly abandoned in favour of an African origin\nof H. sapiens. With the new dating of Liujiang, it is now in the category of an interesting\nbut not very significant discovery at an international level.\nAs I suggested previously, the redating and skeletal descriptions are certainly worth\npublication in a journal such as Journal of Human Evolution, where the new evidence\ncan be read by the relatively small community familiar with the human skeletal record\nof China and SE Asia.\nAR (authors’ reply): Thank you so much for your positive comment on our main\ncontribution: “clearly establishes the age of the Liujiang partial skeleton as between\n~33 and 24 ka”. Additionally, we have mentioned in the last letter that the Liujiang\nhuman fossils have gained international significance as a representative of early modern\nhumans in East Asia. With these new dates we obtained in this study, the Liujiang\nhuman fossils now serve as important material for understanding the dispersal of\nmodern humans across Eurasia in the Later Pleistocene.\nReviewer #5 (Remarks to the Author):\nDear Authors,\nThank you very much for your detailed response to my suggestions and clear layout of\nthe steps you took to integrate the suggestions into your manuscript. I think the\nmanuscript does flow better now and the message/story of the work is clear and I am\nhappy to recommend it ready for publication.\nAR: Thank you so much for your positive comments on our work!\nI noticed these spelling errors, I am sure they can be fixed quickly:\nPage 6 line 150 mongloid, should be mongoloid?\nAR: You are right, it has been corrected in our revised manuscript.\nPage 17 line 384 pyriform aperture should be piriform aperture\nAR: Thank you, it has been corrected in our revision.\nReviewer #6 (Remarks to the Author):\nThe authors have addressed all my comments properly. I am happy to support\npublishing this paper in Nature Communication.\nAR: Thank you so much for your positive comments on our work!\nJust a few minor points to be corrected:\n-Line 744 in the main text: “except for some a sample” should be revised to “except for\nsome samples”.\nAR: Thank you, it has been corrected into “except for samples”.\n-Line 763 in the main text: “to detect the recycling ratio measurement” may be revised\nto “to determine the recycling ratio”\nAR: OK, corrected.\n- reference #111 in the supplementary materials is not about luminescence dating.\nPlease cite the right reference.\nAR: Thank you, this reference has been replaced by “Fu, X., Cohen, T. J. & Arnold, L.\nJ. Extending the record of lacustrine phases beyond the last interglacial for Lake Eyre\nin central Australia using luminescence dating. Quaternary Science Reviews 162, 88-\n110 (2017).” in our revised Supplementary Information."}, "author_response": ""}]

Decision letter