Mathieu Duval

Hominin and faunal fossil collections are valuable scientific resources for investigating past populations, making it critically important to preserve these rare materials and prioritise minimally destructive methods. Electron spin resonance (ESR) dating of tooth enamel typically requires laboratory irradiation of powdered subsamples; however, the effects of this treatment on organic biomolecules, and therefore their potential reuse for amino acid geochronology (AAG), remain largely unknown. This study investigates the impact of gamma irradiation on amino acids within tooth enamel, and its implications for reuse of leftover ESR-dated enamel for AAG from two palaeolithic sites: Hortus, southern France and Belle-Roche, Belgium (maximum laboratory gamma dose of 1500 and 3000 Gy respectively). Our results show that laboratory irradiation induces negligible racemisation in selected amino acids, although significant correlations between dose and D/L values emerge at higher doses (> 1200 Gy). This demonstrates that while low-level gamma irradiation (e.g. <500 Gy) does not substantially compromise the chemical integrity of amino acids in enamel, higher doses may alter racemisation patterns, potentially affecting AAG interpretation. Consequently, this supports cautious reuse of irradiated ESR powders, preferably those exposed to low laboratory doses, enabling effective reuse of finite fossil tooth enamel resources.

The Levant is a key biogeographic corridor, yet historical instability has limited research creating a polarization toward its southern region. To address this geographical bias, we reassessed three legacy faunal collections from Lebanon: Naame, Nahr Ibrahim, and Ras el-Kelb. For the first time, we obtained direct dates for these assemblages and, through zooarchaeological methods, dental wear analysis, and landscape modeling, reconstructed aspects of ungulate and hominin ecology and behavior. The results establish chronological control, defining one of the longest paleoecological records in the region spanning from ~400,000 to ~100,000 years ago, and reveal that productive Mediterranean woodland ecosystems persisted along the central Levantine coast throughout much of the Middle and Late Pleistocene, supporting diverse ungulate communities and enabling hominins to practice seasonal, habitat-specific hunting along coastal ecotones. Integrating these findings into the broader Levantine context reveals marked ecological differentiation between central and southern regions, challenging assumptions of regional uniformity and highlighting the importance of spatial variability in reconstructing Pleistocene paleoecology, human behavior, and biodiversity across this major dispersal corridor.

Throughout the Pleistocene, the Levant served as a key land bridge between continents and witnessed repeated hominin dispersals, including the major expansion of modern humans out of Africa. Yet despite this strategic role, the local ecological conditions encountered by hominin populations along the central Levant remain poorly understood. Here, we analyze sequential and bulk δ ¹³ C and δ ¹⁸ O enamel values from eight herbivore species across three Lebanese archaeological sites, Naame, Nahr Ibrahim, and Ras el-Kelb, spanning ~400,000 to ~100,000 years ago, to reconstruct vegetation structure, hydrology, and seasonal temperature regimes experienced by the hominins who lived in this region. Our results show that the central Levant maintained persistently regular Mediterranean seasonality, with consistent summer-winter offsets and minimal chronological change in amplitude across multiple glacial-interglacial cycles, despite pronounced regional and global climatic oscillations. This reliable hydroclimate supported C3-dominated woodlands and mesic, heterogeneous habitats that maintained reliable resources for herbivore communities over nearly 300,000 years. Together, these findings identify the Lebanese coast as a persistent ecological refugium offering resource predictability that likely facilitated repeated hominin occupations and dispersal events through the eastern Mediterranean.

This study investigates the potential short-term fading of radiation-induced Electron Spin Resonance (ESR) signals in quartz grains following gamma-irradiation, a critical issue for the optimization of Single Aliquot (SA) measurement protocols. Through a signal stability experiment carried out on two quartz samples, we evaluated the evolution of the Al and Ti ESR signal intensities over 2 to 8 months after gamma-irradiation. Our results indicate that the variation of the ESR intensities remains within typical experimental uncertainties, although data might also suggest a potential trend during the first day after irradiation. This trend is, however, non-systematic and could be sample- and signal-dependent, if not directly related to the stability of the experimental setup. Regardless, for precaution we may nevertheless recommend waiting for 1 day after gamma-irradiation before carrying out the ESR measurements. Importantly, this finding implies that ESR measurements of quartz samples can be performed relatively soon after gamma-irradiation, enabling the implementation of more time-efficient SAR protocols for ESR dating applications.

More than five decades after the first report of fossil remains found in a limestone quarry near Crespià, NE Spain, we provide here the first dating results for the palaeontological assemblage from Incarcal‐I, one of the various fossil‐rich sinkholes identified at the locality that has yielded ~2,000 remains representing at least 15 taxa of large mammals. Palaeomagnetism in conjunction with combined U‐series and electron spin resonance (ESR) dating of fossil teeth consistently constrain the age of Incarcal‐I to the latest part of the Early Pleistocene. Specifically, with palaeomagnetic results showing reverse magnetic polarities for the large majority of the samples and no indisputable evidence of normal polarity in the stratigraphic succession, the deposits may be reasonably correlated to the Matuyama Chron (2.61–0.77 Ma), thus providing a minimum age constraint of 0.77 Ma for the sedimentary infill. Additionally, direct dating of two fossil teeth of Hippopotamus antiquus using the most advanced analytical procedures, through a combination of unusually high sampling density ( n = 17) for bulk ESR and U‐series analyses and high‐resolution laser ablation Inductively Coupled Plasma‐Mass Spectrometry (ICP‐MS) analyses, yields a mean age of 862 ± 52 ka (1σ). Interestingly, the data set collected shows the exceptionally high spatial homogeneity of the ESR and U‐series data across dental tissues and of the natural radioactivity of the sedimentary environment. Furthermore, the uncertainty around the uranium uptake modelling carries very little weight in the age calculation, which is unusual for such old fossil teeth. Consequently, this set of evidence supports the robustness and reliability of the ESR chronology, adding a new solid chronological tie point for biochronological inferences. In summary, the various lines of evidence available enable confident positioning of Incarcal‐I in the latest part of the Early Pleistocene, that is, somewhere between the end of the Jaramillo Subchron (1.01 Ma) and the Matuyama–Brunhes boundary (0.77 Ma). The numerical dating results indicate that the fossil assemblage of Incarcal‐I is coeval with those from other well‐constrained key Spanish localities such as Atapuerca Gran Dolina TD4‐6, and Vallparadís Station EVT7, highlighting the overall exceptional density of the Iberian fossil record between ~0.8 and ~1.0 Ma. Finally, a critical evaluation of the existing age constraints available for the Calabrian (1.80–0.77 Ma) fossil localities of the Iberian Peninsula is also proposed here, with a first tentative classification of the sites into four main categories (A to D) based on the robustness and precision of their chronostratigraphic framework.

In this study, we investigate the impact of X-rays produced by conventional mCT instruments on fossil materials dated by radiocarbon. Our results clearly show a decrease on the collagen preservation in fossil and modern bones and teeth, and therefore on the radiocarbon analytical results (in particular, the collagen yield and, possibly, stable isotope composition), after mCT scanning. In other words, all the samples analysed here have experienced a noticeable radiation damage, regardless of their nature (bone and dental tissue) and age (modern and fossil). Given these observations, a prudent approach would be for radiocarbon laboratories to expect lower collagen yields for samples that have been previously mCT scanned and ensure appropriately sized standards are processed alongside these samples. Additionally, samples with originally low collagen yields might become unsuitable for radiocarbon dating after mCT or at least show a yield lower than the usual minimum cut-off value. In this case, it might be viable to extend the collagen yield quality assurance parameter for mCT scanned bones and teeth and instead focus on the C:N ratio as the most appropriate indicator of collagen quality, although we cannot exclude that the latter may also be impacted by X-ray exposure. Further investigations on a larger set of samples are required to confirm these first observations. Nevertheless, in the light of these results, we can reasonably conclude by recommending caution regarding the systematic and unlimited use of mCT scanning in palaeoanthropology or in other related disciplines involving fossil material.

Humans emerged across Africa shortly before 300 thousand years ago (ka)^1–3. Although this pan-African evolutionary process implicates diverse environments in the human story, the role of tropical forests remains poorly understood. Here we report a clear association between late Middle Pleistocene material culture and a wet tropical forest in southern Côte d’Ivoire, a region of present-day rainforest. Twinned optically stimulated luminescence and electron spin resonance dating methods constrain the onset of human occupations at Bété I to around 150 ka, linking them with Homo sapiens. Plant wax biomarker, stable isotope, phytolith and pollen analyses of associated sediments all point to a wet forest environment. The results represent the oldest yet known clear association between humans and this habitat type. The secure attribution of stone tool assemblages with the wet forest environment demonstrates that Africa’s forests were not a major ecological barrier for H. sapiens as early as around 150 ka.

A new granite-doped concrete block with 60 cm x 60 cm x 60 cm dimensions has been built at CENIEH, Burgos, Spain, for dosimetry calibration and cross-referencing purposes. Independent evaluations of the block’s gamma dose rate using passive Al2O3:C dosimeters and various field gamma spectrometer (NaI) probes produce consistent results of 1495 ± 51 μGy a-1 and 1514 ± 43 μGy a-1 (or 1537 ± 19 μGy a-1, depending on the evaluation procedure employed), respectively. Bulk radioelement concentrations calculated from field gamma spectrometry using the Windows method are as follows: K = 1.58 ± 0.08 %, U = 4.26 ± 0.28 ppm, and Th = 12.62 ± 0.72 ppm. This new block complements existing dosimetry reference materials accessible at other laboratories and is available for the broader trapped charge dating community to use for instrument calibration, reproducibility assessments and intercomparison studies.