# An expedient bone tool used for flaying carcasses by Neanderthal at the Abri du Maras (France)

Luc Doyon, Juan Marín Hernando, Marie-Hélène Moncel, Maïlys Richard, Francesco D'errico

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Luc Doyon, Juan Marín Hernando, Marie-Hélène Moncel, Maïlys Richard, Francesco D'errico. An expedient bone tool used for flaying carcasses by Neanderthal at the Abri du Maras (France). 2025. [hal-05340811](https://hal.science/hal-05340811v1)

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# An expedient bone tool used for flaying carcasses by Neanderthal at the Abri du Maras (France)

Luc Doyon

luc.doyon@u-bordeaux.fr

Université de Bordeaux, UMR5199 PACEA, CNRS, MCC; Pessac

Juan Marín Hernando

Universidad Nacional de Educación a Distancia, UNED

Marie-Hélène Moncel

UMR 7194-CNRS-MNHN, Institut de Paléontologie Humaine

Maïlys Richard

Archéosciences Bordeaux, UMR 6034 CNRS, Université Bordeaux Montaigne

Francesco d'Errico

Université de Bordeaux, UMR5199 PACEA, CNRS, MCC; Pessac

## Article

**Keywords:** Bone technology, use wear, confocal microscopy, surface texture, Middle Paleolithic, cultural evolution

**Posted Date:** July 3rd, 2025

**DOI:** https://doi.org/10.21203/rs.3.rs-6931252/v1

**License:** This work is licensed under a Creative Commons Attribution 4.0 International License.

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**Additional Declarations:** No competing interests reported.
**Abstract**

Bone tool use is a hallmark of hominin behavioral evolution, yet its significance in Pleistocene contexts remains underexplored. We present a multi-method analysis of a bone fragment from Abri du Maras (Marine Isotope Stage 5, France), integrating qualitative use-wear assessment with quantitative 3D surface texture analysis via confocal microscopy and linear discriminant modeling. Results indicate that smoothing on the tool's tip resulted from repeated contact with soft tissues, consistent with carcass flaying. This function diverges from the commonly proposed interpretation of such tools being used for hide processing and aligns with ethnographic analogs. Its presence at a seasonal Neanderthal campsite suggests strategic technological planning in subsistence practices. Our findings demonstrate the diagnostic value of quantitative use-wear analysis and call for re-evaluation of osseous tools, offering refined insights into Neanderthal cognition and cultural complexity.

**Introduction**

The use of bone as tools is a behavior unique to our lineage. The earliest evidence for bone technology comes from South and East African sites, some of which were dated to 2.4 Myr[1-10]. Recent discovery of a large assemblage found *in situ* within a single layer of the Oldupai (originally misnamed as Olduvai) T69-Complex suggests that, by 1.5 Myr, some hominin groups implemented a standardized technological strategy that entailed the selection of specific skeletal elements from hippos and elephants, their systematic modification by direct percussion to produce a recurring shape and the use of these tools in percussive and compressive activities[5]. Our understanding of the role played by expedient bone technologies in Pleistocene cultural systems remains nonetheless fragmentary. In Europe, for instance, discoveries made over the last decades leave no doubts that Neanderthal and pre-Neanderthal groups understood the properties of osseous materials and exploited them to make tools. This assertion is supported by evidence for the use of bone to detach flakes from cores, to shape and retouch the cutting edges of stone tools, to produce bone tools with cutting edges shaped by knapping, and to transform more pliable materials[11-34]. Among this latter category, the most frequent functional hypothesis to explain the presence of recurrent polish and rounding on the tip of rudimentary objects pertains to their suggested use as tools for hide processing activities[11,21-25].

Initially, the discovery of hide processing tools was interpreted as indicative of an innovation at the end of the Neanderthal trajectory where ribs were targeted for this task owing to their standardized distal morphology[21]. Similar finds at Châtelperronian (45-40 ka cal. BP) sites from France suggested a continuity, both biological between the authors of the last Middle Paleolithic industries and the Middle to Upper Paleolithic transition industries, and cultural, between the Mousterian of Acheulean Tradition – Type B (MTA-B) and the Châtelperronian[35] lithic technocomplexes. However, research conducted in the last decade now demonstrates this innovation is likely much older than previously thought and not limited to Southwestern Europe. Several unmodified bone fragments found at sites located in Germany,
Italy, Central Asia, Altai, China and North Africa from contexts dated to 380 to 45 ka were interpreted as expedient tools used for hide working[11,36-41].

Unmodified bone tools have traditionally received limited focus by archaeologists. Historically, skepticism inherited from the reinterpretations[42-45] of the Alpine Mousterian[46] and the so-called Osteodontokeratic Culture[47] encouraged the development of taphonomic approaches in archaeology[44,45,48-51] but delayed formal investigations in the potential role played by rudimentary osseous technologies in the implementation of subsistence activities. Ethnographic data nonetheless suggests that unmodified bone fragments may be used for a wide variety of tasks[e.g., 52], including butchery and carcass processing[e.g., 53] as well as acquiring and transforming plant materials[e.g., 54]. Yet, archaeologists interested in documenting early expedient tools face two major challenges. First, recognizing expedient tools is a challenging task. Although experimental archaeology allowed the definition of clear criteria to identify bone fragments intentionally modified by knapping[1,55-58], detecting unmodified bone fragments used as tools in large faunal assemblages primarily relies on the recognition of clear use wear patterns. Unfortunately, during the transition from the biosphere to the lithosphere, taphonomic processes may alter, even erase, use wear patterns, and at times, produce confounding surface modifications similar to anthropogenic modifications. Distinguishing between natural and anthropogenic bone surface modifications therefore constitutes a first challenge that must be overcame. Second, establishing the function of expedient bone tools in reproducible and reliable ways is not an easy task. Historically, the focus given to butchery and carcass processing activities[e.g., 59-62] has biased our interpretations on the role of rudimentary tools in past subsistence. Indeed, items bearing smoothed, polished surfaces are almost systematically interpreted as tools used in hide processing activities[21-25,35]. Yet, hide processing can be achieved in multiple ways, e.g., on fresh, dry or rehydrated skin, with or without abrasive, and each variant resulting in use wear patterns that differ in nature and extent[for a synthesis and experimental demonstration, see 63]. Furthermore, experimental data demonstrates that the use of bone fragments in other carcass processing activities may produce wear patterns qualitatively similar to those resulting from hide processing. To overcome this interpretative limitation, efforts must be pursued to develop the field of quantitative use wear study.

To that end, the recent analysis of the beveled bone tools from Sibudu exemplifies the pertinence of combining qualitative and quantitative approaches in use wear analysis to overcome these two challenges. Rather than serving as hide processing tools, it was shown that these objects were used to debark trees and dig in humus-rich sediments between 80 and 60 ka[64]. Similarly, Ma et al. [63] demonstrated that it was possible to accurately set apart carcass processing activities and several hide processing variants by combining qualitative and quantitative approaches. A similar approach allowed to document the use of bi-pointed object as wool weaving implements and the use of bone awls in textile working activities at the Late Neolithic site of Cueva del Torro, Spain[65], and identify threshing sledges used for processing large amount of cereals during the Early and Middle Neolithic in Greece[66]. Here, building on these methodological advances that rely on quantitative surface texture analysis, we
document a shaft fragment of a reindeer femur bearing, at one end, a highly smoothed area. The object was found at the Abri du Maras, layer 5 upper, a context dated to the Marine Isotope Stage (MIS) 5 (Fig. 1). We apply discriminant analysis of surface textural data to confirm that the smoothed area originates from the use of the tool rather than from taphonomic alterations and to establish the function of this unique object. Our results show that the tool was likely used to flay carcasses, i.e., an activity that aims to detach the skin from the body of an animal without damaging it. Our results demonstrate the potential of quantitative use wear studies to overcome limitations inherent to uncovering the role of rudimentary bone tools in past cultural systems. In doing so, they provide a new outlook at Neandertal subsistence strategies by providing a means to investigate the transformation of perishable materials during the Paleolithic.

[Figure 1 about here]

## Archaeological context

The Abri du Maras is a site located in the Ardèche Gorges on the southeastern margins of the Massif Central (Fig. 1). The Abri du Maras is a largely collapsed rock shelter. The first excavation at the site occurred in the 1950s and 1960s by R. Gilles and J. Combier[67]. Since 2006, new excavations of an 88 m² area revealed an up to 7 m-thick multi-layered stratigraphy subdivided into six units numbered from 1 (top) to 6 (bottom) based on geological and sedimentary observations. Two main phases of roof collapse of a vast cavity are recorded between layers 2 and 3 on the one hand and layers 4 and 5 upper on the other hand. Most of the archaeological material was recovered in layers 4, 5, 5 upper and 6. Layer 4 was subdivided into two main occupation phases, i.e., 4.1 and 4.2, based on vertical and horizontal variations in the density of archaeological remains identified during post-excavation spatial analyses. The upper part of layer 5 (layer 5 upper) was subdivided into three main occupation phases for the same reasons, i.e., 5.1, 5.2 and 5.3[68,69]. The object reported here was unearthed during the 2017 excavation of level 5.1 in square L6 (x: 70; y: 47; z: 399) and was attributed the accession number Mar’17-L6-5-1539 (Fig. 2). Recent multi-method dating of layer 5 upper suggests that its formation occurred between 127 ± 17 ka (optically stimulated luminescence, OSL, on quartz)[70] and 90 ± 9 ka (electron spin resonance combined with uranium-series, ESR/U-series, on tooth enamel)[71], which makes it coeval with MIS 5.

For layer 5-upper, lithic technology primarily relies on flint sourced from local and semi-local outcrops near the site, with additional material coming from more distant southern sources. The lithic assemblage suggests a long-term occupation, characterized by diverse core reduction methods and high frequency of retouched flakes compared to the upper part of the sequence. The numerous tiny retouch flakes attest to a high consumption of flakes of various sizes at the site, including some that were knapped elsewhere. Notably, the assemblage includes semi-Quina tools and Quina products[69], which raises questions about the definition of a Rhodanian Quina facies. *In situ* core reduction strategies encompass discoid, orthogonal, multidirectional and Levallois methods, along with cores on flake. Evidence of *Alnus* roots working is documented in the layer[72].
From a zooarchaeological perspective, the occupation of level 5.1 at Abri du Maras presents characteristics typically associated with residential camps. The presence of *Rangifer tarandus* (74%), *Cervus elaphus* (11.3%), *Equus ferus* (10.7%), *Bison priscus* (2.8%), *Capreolus capreolus* (0.6%) and *Sus scrofa* (0.1%) suggests an open landscape with forest patches which likely provided Neanderthal groups with a wide range of opportunities to carry out their hunting and foraging activities[73]. Although isolated teeth constitute the majority of identified remains by taxon, the skeletal element representation for the dominating species, i.e., Cervids, reveals an abundance of appendicular elements with post-cranial axial elements being less frequent. Mortality profiles indicate a preference for hunting prime adult individuals across all species. Seasonal evidence suggests reindeer were hunted in summer while horse hunting occurred throughout summer and into early autumn[73].

Bone surface preservation on specimens recovered from layer 5.1 is generally good, with more than three quarter of the assemblage (78.6%) displaying intact surfaces over two-thirds or more of the cortical bone. Root etching is the most frequent post-depositional alteration affecting more than a quarter (28%) of the remains. Small fissures and desquamations were recorded on 8% of the specimens, which indicates the sub-areal exposure of the faunal assemblage for a moderate period prior to its burying. Black stains of manganese oxide in the form of dendrites are common (20%). Orange spots caused by iron oxide precipitation are also recorded albeit at a lower rate (3.8%). Carnivore modifications are scarce (0.7%).

Anthropogenic modifications are frequent on the faunal remains recovered in level 5.1: 32.8% display signs of exposure to heat, 8.3% bear cut marks and 8.3% percussion marks likely produced when fracturing the bone to access marrow. Green fractures are present on most bone fragments which lends further support to marrow extraction activities taking place at the site. A total of 18 bone fragments exhibits well defined areas on their cortical surfaces with overlapping pits and linear marks indicating their use as retouchers for shaping lithic cutting edges[73]. The abundance and distribution of cut marks suggest that hominins had primary access to animal carcasses. Furthermore, numerous reindeer metapodials bear cut marks that appear to be related to the removal of the skin and tendons. Overall, the faunal assemblage indicates that Abri du Maras functioned as a long-term seasonal campsite, primarily occupied during the summer, and occasionally into early autumn. High-caloric portions of prime adult ungulate carcasses were transported over relatively short distances and processed at the site, as evidenced by the abundance of teeth and antlers.

## Results

The MAR'17-L6-5.1-1539 specimen (Fig. 2a) is a shaft fragment of a reindeer left femur measuring 133.3 mm in length, 26.9 mm in width, 13.7 mm in thickness and 4.0 mm in maximum cortical thickness. It preserves the antero-lateral face of the midshaft and one-third of its total circumference. All fracture planes are smooth; they are fairly abrupt on one side and curved with an oblique angle on the other. Together, these features indicate the femur was broken while still being fresh. On the cortical surface of the anterior aspect, an isolated flake removal scar is interpreted as resulting from the breakage of the
bone to access marrow. Localized ferro-manganese oxide aggregations in the form of dendrites and coloration by precipitations are visible on the bone surfaces (Fig. 2a). Evidence of root-etching are recorded on the cortical and medullar aspect of the object (Fig. 2a). Incipient fissures oriented longitudinally along the femur's main axis (Fig. 2a) suggest a moderate weathering of the object resulting from subaerial exposure, i.e., stage 1[48]. These taphonomic alterations do not together prevent the recognition of a rounded, worn surface located at the distal tip of the object.

Through the naked eye, the distal end displays a bifacial flattening of its surface in the form of a bevel (Figs. 2b,c). Deformations and compaction of the cortical bone are visible on the cortical and medullar aspect of the object as well as on the fracture planes. The edges are rounded and worn, and their smooth surfaces give them a polished sheen. On the cortical surface, this wear pattern extends up to 21.4 mm from the apex while it is slightly less invasive on the medullar surface with a maximal extent of 19.7 mm. The small difference recorded between the cortical and medullar surface suggests that both faces of the distal end were simultaneously in contact with the worked material over a prolonged period. Two micro-flake removal scars are present near the center of the apex (Figs. 2b,c,d,f). The one on the medullar aspect displays a patina that differs from the adjacent surfaces and the rest of the object (Fig. 2c), which suggests a recent damage. Conversely, the one on the cortical surface presents a patina similar to adjacent areas which suggest this damage likely occurred prior to the abandonment of the object at the archaeological site (Fig. 2b). No evidence of distal and proximal compression or flaking typical of intermediate pieces[e.g., 74,75] were detected.

At low magnification, the working edge is highly smoothed and display a homogeneous surface without striations (Fig. 2c). The vascular canal openings usually found on intact bone surface are no longer visible. On the cortical aspect of the object (Figs. 2d,e), the density of micro-striations increases the further we move away from the apex. They are variable in width and display smooth outlines with few or no hertzian cones. The finest striations are preferentially oriented along the main axis of the object while the larger and deeper ones are obliquely oriented relative to this axis. Irrespective of their size, the striations overlap one another without clear recurring patterns in their relative arrangement. Micro-striations overlapping the flake removal scar located at the center of the apex on the cortical surface and adjacent cortical surface by a few millimeters suggest the object continued to be used after the damage occurred. On the medullar aspect of the object (Figs. 2f,g), subparallel micro-striations extend from the right lateral edge across the oblique fracture plane. Their size is relatively homogeneous although coarser striations become visible the further we move away from the apex.

At high magnification, smoothed surfaces display evidence of intense flattening and homogenization (Fig. 3a). This pattern is particularly evident with the partial filling of the bone microstructure. Variations in texture (Fig. 3b-d), especially the rugged edges between dales and plateaus on the fracture planes, likely results from weathering. Nonetheless, micro-striations are preserved on flat areas where the bone structure is more homogeneous. As we move away from the apex, the micro-striations become more visible despite the alteration of their contours by taphonomic processes. Their width varies between 3 and 12 µm and their depth rarely exceeds 1.5 µm. The range of their length is difficult to establish
because the majority are interrupted by taphonomic alterations. Nonetheless, the best-preserved striations often extend beyond the field of view, which entails length surpassing 320 µm. In cross-section, they display an open U-shaped profile, with rare instances of V-shaped profile. Overall, these observations at low and high magnification suggest the tool was in a prolonged contact with soft pliable material.

[Figure 3 about here]

Quantitative surface texture analysis lends further support that the wear pattern described above results from tool use rather than taphonomic alterations. Regardless of the surface type – cortical, medullar or fracture planes – the values extracted from worn surfaces differ significantly from those of taphonomically altered surfaces (Supplementary Figures S1–S3; Supplementary Table S1). This result is particularly evident when considering the skewness of height distribution (Ssk), the auto-correlation length (Sal), the texture aspect ratio (Str), the density of peaks (Spd), the mean hill volume (Shv), the standard deviation of dale roughness (Sdrnq), the length-scale anisotropy (epLsar), the heterogeneity of fractal complexity (HAasfc81), the median absolute deviation of fractal complexity (MadAsfc), and the mean depth of furrows (Mea Dep Furr). The linear discriminant analysis (LDA) and cross-validation canonical variate analysis (cv-CVA) accurately discriminate between “worn” and “taphonomic” surfaces more than 92% of the time for the cortical and medullar surface (cortical surface: LDA accuracy = 97.06%, LDA kappa = 92.70%, cv-CVA accuracy = 97.47%, cv-CVA kappa = 94.02%; medullar surface: LDA accuracy = 93.75%, LDA kappa = 88.10%, cv-CVA accuracy = 94.87%, cv-CVA kappa = 88.89% (Supplementary Figs. S4a–d; Supplementary Tables S2–S5). Discrimination between “worn” and “taphonomically altered” fracture planes yields slightly lower accuracy results albeit remaining above 80% (LDA accuracy = 88.46%, LDA kappa = 76.07%, cv-CVA accuracy = 83.93%, cv-CVA kappa = 66.11%) (Supplementary Figs. S4e,f; Supplementary Tables S6, S7). Thus, the qualitative differences observed between the “worn” area and the rest of the object combined with the variation in quantitative surface texture data support an anthropogenic rather than a taphonomic origin for the alteration.

The surface texture analysis on experimental objects identified 16 variables apt to discriminate between the various activities included in the comparative sample. They include the auto-correlation length (Sal), the texture aspect ratio (Str), the texture direction (Std), the mean hill area (Sha), the hill count (Shn), the mean hill roughness (Shrn), the standard deviation of hill roughness (Shrnq), the standard deviation of dale roughness (Sdrnq), the length-scale Y-max (Ymax_L), the new length-scale anisotropy (New_epLsar), the heterogeneity of the fractal complexity (HAasfc81 and HAasfc), the mean density of furrow (Mea_Den_Furr), and the first three directions of the texture (Dir_1st, Dir_2nd and Dir_3rd) (Supplementary Figures S5–S7). The LDA results suggest the use wear pattern present on the object corresponds to those produced experimentally in activities that entailed a prolonged contact with soft animal tissues. The archaeological pattern differs markedly from those generated by tasks that involve abrasives – such as digging in soil, processing plants or treating hides with sand or ochre – which produce dense, deep and uniformly oriented striations that cover the tool surface (Fig. 4). On the Abri du Maras specimen, the striations are sparsely distributed and significantly shallower indicating that the
tool was unlikely used in such abrasive contexts (Fig. 4). Although the observed wear resembles that
generated while flaying, experimental use of bone tools on fresh or rehydrated hides without abrasive
typically results in both striations and pits, the latter being absent on the archaeological specimen (Fig.
4). To refine the functional interpretation, both LDA and cv-CVA point to carcass flaying as the most
probable activity (Fig. 5, Supplementary Figures S8, Supplementary Tables S8–S10.). This classification
is based on a high posterior probability (Fig. 5; Supplementary Figures S8; Supplementary Tables S8–
S10), supporting a robust statistical match with experimental flaying traces. While we acknowledge the
possibility that the tool may have been used in an untested activity, the strength of the discriminant
classification, combined with the distinctive absence of abrasive-related features, makes flaying the
most parsimonious explanation. The few discrepancies between the archaeological specimen and the
experimental sample likely reflect variability in wear caused by the contact with fresh meat and the
effects of post-depositional processes.

[Figures 4 and 5 about here]

Discussion

The tool discovered at Abri du Maras, level 5.1, provides further evidence of Neandertals using unmodified bone fragments during the end of MIS5. Our discovery opens a new perspective on the subsistence strategy implemented by the human groups that occupied the Rhône Valley and on the cultural adaptations they resorted to in their daily and seasonal activities. Textural and discriminant analyses indicate that this object was most likely used in flaying activities that produced a use wear comparable to our experimental sample. Interestingly, the function of the Abri du Maras tool is not linked to hide processing, with which similar objects, e.g., the objects interpreted as smoothers (fr. *lissoirs*), have been traditionally associated. The identification of this object is entirely consistent with ethnographic and archaeological data. Comparable ethnographic examples from the Algonquian Nehiyawak and Nakawēk nations of North America reveal that elongated unmodified bone fragments were sought after for flaying carcasses because they could be inserted between the skin and the meat to efficiently detach these soft animal tissues without piercing or cutting the hide in the process[53], a risk that would increase if lithic tools were used to perform this task.

From an archaeological perspective, the presence of an object used for flaying carcasses is entirely compatible with the interpretation of the Abri du Maras being a long-term occupation site visited during the good season. Throughout the summer and the beginning of the fall, the Neanderthal visitors could intercept the migratory species that were present in the vicinity of the site. The targeting of prime adult individuals and processing of caloric-rich body parts at the site, especially breaking the bones to access marrow, would likely have produce a wealth of bone fragments of various size and morphology from which to choose an ideal specimen that had the affording characteristics to flay carcasses. The preferential introduction of specific body parts at the site entails that the initial phases of the butchery and carcass processing activities didn't take place at the site but rather in its vicinity. The highly smoothed edges of the object suggest that the flaying tool was used over an extended period. As such, it
is reasonable to hypothesize that it was likely transported on several occasions in the toolkit carried by an individual who participated in daily hunting or lithic procurement trips through the season of occupation at the site. This scenario not only implies that Neanderthals understood the technological potential of bone and took advantage of it. It also highlights their capacity to plan their technological needs ahead and select lightweighted items that could efficiently perform the tasks that would arise following a successful kill.

This discovery has also important implications for the evolution of clothing and the production of bags, particularly among Neanderthals. The use of a bone tool to avoid perforating the hide suggests that Neanderthals took care to preserve impermeable skins, likely to produce waterproof clothing. Additionally, this practice implies that such garments were made from large or complete hides, as perforations would have been less problematic for clothing constructed from smaller pieces, where undamaged sections could be selectively used[76,77]. The emphasis on maintaining intact hides further supports the idea that Neanderthals developed strategies to maximize the functional properties of their garments. Furthermore, at the same site, though in a more recent layer, there is evidence of a complex twisted thread made from tendons and plant fibers by Neanderthals[78,79]. This suggests an ability to manufacture robust clothing or bags, reinforcing the notion that Neanderthals not only processed hides with care but also had the technological means to assemble durable and functional garments.

Finally, our results highlight the fact that osseous materials are particularly apt to keep a record of object-matter interactions, especially when these interactions are made in the context of anthropogenic subsistence activities. The methodology we implemented relies on combining two complementary approaches, i.e., the traditional qualitative use wear documentation and the emerging quantitative use wear analyses relying on surface texture data. These two approaches go hand in hand. While qualitative observation may help identifying use wear patterns and propose a first hypothesis on the nature of the material the bone tool encountered, the quantitative methods are crucial to confidently assess that the purported use wear indeed differ from taphonomic alterations, and to narrow down the type of human action that most likely led to its development. In the future, it would be worth reassessing the numerous objects interpreted as smoothers with the complementary methods presented here to test whether they were indeed used for processing hides or served to fulfil other tasks.

# Materials and Methods

Fieldwork at the Abri du Maras follows standard archaeological excavation protocols including the three-dimensional recording of stone tools, large mammal bones, visible features, etc. Smaller finds are bagged by 1-m² unit of provenience. Sediments are dry-sieved using a 2-mm mesh screen. The bone tool documented here was identified by one of us (JMH) during the zooarcheological analysis of the faunal assemblage recovered from level 5.1. Taxonomic and skeletal element identification was carried out by comparing the bone fragment with faunal remains from the zoological reference collection curated at the Muséum National d'Histoire Naturelle, Paris, France. Morphometric data, i.e., maximum length, width, and thickness, were collected using a digital caliper. Anthropogenic modifications were distinguished
from natural ones based on criteria available in the literature[44,45,48,50,51,80-82]. The object was
photographed with a Sony A6400 equipped with a Sony E 30-mm F3.5 macro lens. Microscopic
observations were conducted using a motorized Leica Z6 APOA equipped with a BFC420 digital camera
linked to a LAS Montage and Leica Map DCM 3D computer software at the PACEA laboratory. These
observations were done both on the original object in reflected light and on transparent resin casts of the
object in transmitted light. High-resolution surface acquisition was obtained using a MarSurf CM mobile
confocal microscope driven by MarSurf MSW 8.6 software. This equipment was used with the aim of
characterizing the roughness of worn and unworn areas and producing 3D renderings of the used
surface. Acquisitions were done using a 50x magnification lens with a working distance of 10.6 mm
(field of view: 323,4 x 323,0 µm). To ensure quality, surfaces with less than 95% measured points were
systematically re-acquired. Post-acquisition treatment was carried out using the Mountain View 8.2
software and followed a procedure adapted from Ma et al.[63] and Mazzucco et al.[66]. First, a data
augmentation procedure was implemented to better capture the range of variation in surface texture.
Consequently, each acquisition was subdivided into five overlapping areas measuring 200 x 200 µm
respectively located at the four corners of the original acquisition without touching the edges and at its
center. Then, using built-in operators, each sub-area was processed using standard protocol that entails
levelling the surface (least square method), removing outliers (both isolated and close to the edge),
removing points outside of 0.01% and 99.99% threshold for height distributions, filling-in non-measured
points (interpolating values from neighbors), removing form (polynomial of fifth order) and applying
metrological filter (Gaussian 25µm) to distinguish between the waviness (S-F) and the roughness (S-L)
of the object. Roughness parameters (ISO 25178), fractal parameters (SSFA), furrow analysis parameters
and texture direction and isotropy parameters were extracted on the S-L surface (Supplementary Table
S1 for definitions; Supplementary Text S1). Parameters expressed in percentages, ratios and angles were
transformed into linear variables centered around zero to allow their use in multivariate analysis (see
below). Surface texture images were produced using the 'viridis' color ramp to help visualization for
colorblind individuals.

A preliminary data exploration was done to remove variables with missing values (Supplementary Text S2). To ensure that the worn area resulted from the use of the bone fragment, they were first compared with unworn intact areas along the diaphysis on the cortical and medullar surfaces as well as on the fracture planes. For linear data, the Shapiro-Wilk test was used to assess the normal distribution for each texture parameters. Pairwise comparisons of linear data were done using either the ANOVA test for normally distributed variables or else the Wilcoxon test with Bonferroni correction. For circular data, the Mardia-Watson-Wheeler and the Fisher's non-parametric tests were used to compare sets of angles and their medians between groups. Parameters that displayed significant differences between worn and unworn surfaces (p < 0.05) were retained and those highly correlated were removed (threshold: R² = 0.7). Principal component analysis (PCA), linear discriminant analysis (LDA) and cross-validation Canonical variate analysis (cv-CVA) were performed to securely distinguish between worn and taphonomically altered areas based on their surface texture data. Second, to establish the most likely function of the object, worn surfaces were compared using linear discriminant analysis with an experimental sample
curated in the *ExOsTechBank*, i.e., a database of worn surfaces recorded on archaeological, experimental and ethnographic bone tools which currently includes 8598 surface acquisitions (20 February 2025). Supplementary Text S3 provides a summary of the activities represented in the *ExOsTechBank* and the acquisitions used in the present research. For the present study, six variants of hide working were selected: rehydrated cow and deer hide without abrasive, dry hide with sand, fresh hide with sand, ochre, and marrow. To this sample, experimental use wear produced when flaying carcasses, cutting fresh meat, debarking pine tree, and digging humic soil were also considered. The comparison between the archaeological and experimental samples followed a two-step process. A first attempt was done by comparing the Maras use wear with broad categories of worked material, i.e., hide (irrespective of their state or the use of abrasive and tannins), animal soft tissues, miscellanea (debarking and digging in sediments). A second attempt aimed to refine the category of activity by comparing the Maras use wear with those included in the two categories that were most often predicted. To avoid sample imbalance in the discriminant analyses, the training sample includes 80% of the smallest sample size for any of the groups; all other individuals are assigned to the testing sample. After the testing phase, several statistics were computed including the model's accuracy, kappa, precision, recall and F1-score, etc. The discriminant analyses, i.e., both LDA and cv-CVA, were iterated 1001 times, i.e., from the random creation of the training and testing subsets to the computation of the statistics. The iteration which yielded the best result was then used to predict the most likely function that could explain the use wear pattern identified on the Maras specimen. All analysis were performed in R-CRAN v4.4.1[83]. The code used and the confocal acquisition are available in open access on Zenodo (10.5281/zenodo.15630707).

# Declarations

## Acknowledgements

Permits issued to Marie-Hélène Moncel to conduct research at the Abri du Maras were granted by the Ardèche Prefecture and include the permission to study the material reported in the present study in accordance with French regulations. We thank Camille Daujeard, Palmira Saladié, Antonio Rodríguez-Hidalgo and Anne-Marie Moigne for scientific advice during the Juan Marin Hernando' Phd. We also thank Lloyd A. Courtenay for his help in integrating circular and linear statistical approaches in this project.

## Funding declaration

This study benefited from the financial support from the following agencies: Service régional de l'Archéologie Auvergne-Rhône-Alpes, Ministère de la Culture (MHM); Initiative d'Excellence IdEx, University of Bordeaux, Talent program grant # 191022-001 (Fd'E, LD); French government in the framework of the University of Bordeaux's IdEx "Investments for the Future" program / GPR "Human Past" (Fd'E, LD); Research Council of Norway, Centres of Excellence (SFF), Centre for Early Sapiens Behaviour, SapienCE grant # 262618 (Fd'E); European Research Council Synergy Grant no. 951388 for the project Evolution of Cognitive Tools for Quantification (QUANTA) (Fd'E); European Research Council
Starting Grant no. 101161065 for the project Pleistocene Expedient Osseous Technology (ExOsTech) (LD).

**Author contributions**

Conceptualization: LD, Fd'E

Methodology: LD, Fd'E, MHM

Investigation: LD, JMH, MHM, MR, Fd'E

Visualization: LD, MR, Fd'E, MHM

Funding acquisition: MHM, LD, Fd'E

Project administration: LD, MHM

Supervision: LD

Writing – original draft: LD

Writing – review & editing: LD, JMH, MHM, MR, Fd'E

**Data availability statement**

The R script, surface texture data and confocal acquisitions on the Abri du Maras specimen are available on Zenodo (10.5281/zenodo.15630707). Access to the confocal acquisitions on experimental specimens is granted upon request to the corresponding author. All other data are available in the manuscript and the supplementary information files.

**Additional Information**

The authors promote scientific collaborations based on merit irrespective of an individual's ethnicity, sexual orientation, gender identity, or disability status. The co-authors' order reflects their contribution to the study. The authors declare no competing interests.

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## Figures
<figure><img src="image_2.png" /><figcaption>Figure 1</figcaption></figure>

**Location, excavated area, and stratigraphy of the Abri du Maras.** Location of Abri du Maras in the middle Rhône Valley, France (a). Grid of the excavation with the location of the portions excavated by R. Gilles (light grey), J. Combier (medium grey) and M.H. Moncel (dark grey). The red square indicates the location of the bone tool (b). Stratigraphic sequence, age estimates per layer and location of the bone tool. A mean age was calculated when several ages were obtained using the same method on the same layer (right). Individual ages (one age per method available) are shown on the left (in italic: maximum age). Note that within a layer, the ages are not necessarily represented following stratigraphic order. The
OSL, IRSL and ESR/U-series ages are presented at 1 σ; radiocarbon (¹⁴C) and U-series ages at 2 σ.
Modified from Richard et al. (2021) (c).

<figure><img src="image_3.png" /><figcaption>Figure 2</figcaption></figure>

**Rudimentary bone tool MAR'17-L6-5-1539** found at the Abri du Maras. General (a) and close-up views (b-g) of the worn area on the cortical (b, d-e) and medullar (c, f-g) surfaces observed in low-magnification with incipient on the object (b, c) and transmitted light on resin replicas (d-g). Scales = 1 cm (a), 5 mm (b, c) and 1 mm (d-g).
<figure><img src="image_4.png" /><figcaption>Figure 3</figcaption></figure>

**Use wear patterns on the rudimentary tool from the Abri du Maras.** Sample of use wear patterns observed at high magnification on the on the smoothed edges (a) and fracture planes (b) as well as the cortical (c) and medullar (d) surfaces.
<figure><img src="image_5.png" /><figcaption>Figure 4</figcaption></figure>

3D rendering of natural and worn surface texture on experimental bone tools and the Abri du Maras specimen. Comparison between the natural surface of a reindeer femur (a), the use wear pattern observed on the Abri du Maras specimen (b-d) and the experimental acquisitions curated in the ExOsTechBank (e-n). The experimental acquisitions were done on bone tools used for scrapping rehydrated cow (e), and red deer (f) hide, flaying carcass (g), cutting fresh meat (h), scrapping fresh hide with marrow (i), ochre (j), and sand (k), scrapping dry hide with sand (l), debarking pine trees (m), and digging in humic sediment (n).
<figure><img src="image_6.png" /><figcaption>Figure 5</figcaption></figure>

**Discriminant analyses results.** Linear discriminant (LDA) (a) and cross-validation canonical variate (cv-CVA) (b) analyses results distinguishing different activities involving soft animal tissues with the projection of surface texture data acquired on the Abri du Maras specimen (black stars).

**Supplementary Files**

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* 20250619AbriduMarasScientificReportSI.pdf