Abstract The development of the Azilian in Western Europe 14,000 years ago is considered a “revolution” in Upper Paleolithic Archaeology. One of the main elements of this rapid social restructuring is the abandonment of naturalistic figurative art on portable pieces or on cave walls in the Magdalenian in favor of abstract expression on small pebbles. Recent work shows that the transformation of human societies between the Magdalenian and the Azilian was more gradual. The discovery of a new Early Azilian site with decorated stones in France supports this hypothesis. While major changes in stone tool technology between the Magdalenian and Azilian clearly mark important adaptive changes, the discovery of 45 engraved schist tablets from archaeological layers at Le Rocher de l’Impératrice attests to iconographic continuity together with special valorization of aurochs as shown by a “shining” bull depiction. This evidence suggests that some cultural features such as iconography may lag far behind technological changes. We also argue that eventual change in symbolic expression, which includes the later disappearance of figurative art, provides new insight into the probable restructuring of the societies.

Citation: Naudinot N, Bourdier C, Laforge M, Paris C, Bellot-Gurlet L, Beyries S, et al. (2017) Divergence in the evolution of Paleolithic symbolic and technological systems: The shining bull and engraved tablets of Rocher de l'Impératrice. PLoS ONE 12(3): e0173037. https://doi.org/10.1371/journal.pone.0173037 Editor: Roberto Macchiarelli, Université de Poitiers, FRANCE Received: September 23, 2016; Accepted: February 14, 2017; Published: March 3, 2017 Copyright: © 2017 Naudinot et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: Most of the data are directly available directly in the paper (in the form of a table and pictures for the engravings). Researchers could contact Nicolas Naudinot (nicolas.naudinot@cepam.cnrs.fr) if they need any precision or access to more specific data. Funding: The excavation of this site was funded by: Service Régional de l'Archéologie de Bretagne (Ministère de la Culture et de la Communication), http://www.culturecommunication.gouv.fr/Regions/Drac-Bretagne/La-DRAC-et-ses-services/Annuaire-Organigramme/Pole-architecture-et-patrimoine/Service-regional-de-l-archeologie, and Conseil départemental du Finistère, https://www.finistere.fr/. This is not a grant but a funding for Archaeology from the Ministry of Culture of France. We do not have any grant numbers. Competing interests: The authors have declared that no competing interests exist.

Introduction The Azilian is a culture of the European Upper Paleolithic. It appears at the end of the Magdalenian around 14,000 years ago and precedes the first Mesolithic hunter-gatherers in the early Holocene. This period is critical to the study of cultural evolution as it is characterized by a major restructuring of hunter-gatherer societies in terms of technology (a decrease in stone and bone tool standardization and a simplification of manufacturing processes), settlement (with changes in mobility patterns), and art, with the development of a unique abstract graphic production that contrasts with the previous Paleolithic but also the final Paleolithic “Laborian” figurative iconography (e.g., Lascaux, Altamira) [1–5]. The role that rapid warming and climatic instability of the Azilian period played in shaping techno-economic and symbolic spheres is debated among scholars [6–8]. Based on genetic studies, some other scholars also emphasize the potential role played by the migration of new populations coming from Eastern Europe and the Near East around 14,000 BP [9]. The Azilian has long been considered an abrupt event, a “revolution” in the Upper Paleolithic [10]. Recent work shows that the development of this culture was not sudden but progressive [6, 11–12]. This global process of cultural change began during the GI-1e/d (end of the Bølling) with the Early Azilian (EA) [6, 8, 12–14]. However, the Azilian probably finds its roots at the end of the Magdalenian during the GS-2b-a (Oldest Dryas) [6, 15]. The paroxysm of this process is the so-called Late Azilian (LA), probably lasting to the first half of GS-1 (Younger Dryas) [11]. A new EA rock shelter in the western extremity of Brittany provides critical data to investigate the tempo of technological and symbolic change during the Azilian. The association of a lithic industry with a rich artistic assemblage of 45 engraved (and sometimes charcoaled) schist stones suggests a clear arrhythmia between symbolic production and technological adaptations. Here the possible techno-economic adaptations to climatic changes appear to have had no direct influence on the symbolic and perhaps spiritual universe of the first “Azilian” people who perpetuated an age-old tradition.

1. Methods 1.1. Field work The Rocher de l’Impératrice has been excavated every summer since 2013 and the excavation is still underway (The excavation of the site was authorized by the French Ministry of Culture. French prefectural decrees: 2013–007, 2014–031, 2015–018, and 2016–032). Because of the position of the site at the foot of a quartzite cliff in the middle of a forest, no mechanic equipment is used to excavate the site. Because of the presence of archaeological material, and especially engraved schist slabs, in the entire stratigraphy, no shovels or picks are used, only trowels and precision excavation tools. All artifacts discovered during the excavation are recorded in three dimensions with a total station. All the sediments are water screened (1.5 mm mesh) and all the lithic elements, charcoals fragments, and schist fragments are collected during this procedure. In total, 4659 lithic artefacts have been collected since 2013. Among these remains are 45 engraved schist tablets. The entire collection is temporarily stored at the UMR 7264 CEPAM CNRS at the Université Côte d’Azur in Nice (France) for the time of the study and will be store in an official Ministry of Culture repository in Brittany at the end of the program. 1.2. Technological study of the lithic assemblage The technological study of the lithic assemblage has been developed following the French methodology of Technologie lithique. This method addresses lithic tools as the result of a production process rather than as just a cultural object (see among others [16–19]). This approach considers each lithic artifact in terms of information about the objective of production and the methods. All the information from raw material procurement to the discard of tools is considered, including production methods, curation strategies, and tool function. This method constitutes a particularly efficient tool to investigate cultural changes, since each technical culture develops particular technologies and strategies, and in hunter-gatherer socio-economic organization, since this approach allows studying spatial and temporal organization of the production (chaine opératoire segmentation). 1.3. Preliminary study of the engraved slabs Only a preliminary study of the engraved stones has been conducted so far. Indeed most of the pieces have sediment deposits and crusts on their surfaces which make the identification of the engravings and the deciphering of the lines difficult. A meticulous cleaning will be essential to allow an exhaustive analysis of the etchings technology, forms, and superpositions or “stratigraphy” of the etchings. However, after residues of pigment were found within the engravings on one piece (317 –see below), the choice was made not to clean the other fragments. Moreover, refitting work is ongoing, for new engraved fragments are unearthed each year at the site. Hence, only the main motifs from the two major pieces are discussed here. Although preliminary, analysis of these images have great archaeological significance. And since the deposits on these two stones are restricted, few new motifs are expected to come out of the analytical tracings. “Reading sketches” were made from a photo-mosaic created with pictures taken under different lighting conditions, and according to the classic tracing method used in the study of mobile art. A first technical study was conducted on the most striking decorated set of the series: an auroch’s head surrounded by radiating lines made of very wide and deep engraving (fragment 317 side A). A fine analysis of the engraving (techniques, chronology of the incisions, dyes…) requires a proper cleaning of the tablets. The analysis of the morphology of the incisions (edges and bottom), the regularity and precision of the lines can only be done after a precise observation with selected optical instruments on surfaces cleaned of any sediment. A first light cleaning has pointed out the presence of black pigments in the wide and deep engravings; hence we have opted for a long but non-aggressive protocol to clean the engravings and highlight these deposits. The tablets were cleaned under a microscope for a more precise view of the surfaces. If adhering sediment had chipped, a light lever made with a wooden toothpick removed it. When the sediment was too hard, it was softened with distilled water and then a small strip of fiber-free paper was placed on the soaked area and the sediment removed by transfer. Some areas were left uncleaned to preserve trapped dyes for future analysis. These areas have been selected out of the etching intersections, in order to allow the most complete possible decoding of the chronology of the engraving process. 1.4. Analytical characterization of the engraving black pigment Pigment characterization was achieved non-invasively by Raman spectroscopy using a Labram HR800 (Horiba Jobin Yvon) spectrometer and the blue 458nm line from an Argon Laser (Innova 90C-6 from Coherent). A microscope allows the visualisation of the analysed area and the interfacing of the micro-measurement with the sample through the focusing of the Laser and the collection of the Raman scattering. Long working distance 50x and 100x objectives (Olympus) were used, allowing an area of analysis of about 2 and 1 micrometers, respectively. The Laser power at the sample is set around 100 μW in order to respect sample integrity. The artifact was directly positioned on the microscope stage to perform the non-contact analyses. Such analyses allow the structural identification of the material used as a pigment in order to determine its nature.

2. Le Rocher de l’Imperatrice rock shelter Le Rocher de l’Impératrice is a small rock-shelter approximately 10 m long, 3 m deep and 2 m high located near Plougastel-Daoulas at the western extremity of Brittany (France). The shelter is at the foot of a 50 m high quartzite cliff dominating the Brest roadstead (Fig 1). The site sits about 50 m a.s.l on a southern steep slope overlying Brioverian shale bedrock. The steep topography is covered by silty-clayey solifluction deposits rich in shale flags. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 1. Location of Le Rocher de l’Impératrice rock-shelter (Europe map from Geoatlas, Brittany and local maps L. Quesnel (CNRS)). https://doi.org/10.1371/journal.pone.0173037.g001 Because of the geomorphologic context, the stratigraphic sequence of the rock-shelter is complex. Sedimentary infilling of the shelter begins with alternating facies of lightly reworked loess and solifluction deposits (US-103) (Fig 2). US-103 is cryoturbated and was deposited by short distance solifluction or gelifluction, under periglacial conditions, possibly at the end of the Last Glacial Maximum (MIS 2) or during the beginning of Late Glacial (c. 15, 000 BP). US-103 consists of a reactivation of earlier cryoclastic rock fall and slope deposits (cliff-talus slope system) mixed with reworked aeolian deposits, due to the secondary redistribution of the debris on this slope. US-102, truncating and overlying US-103, is laminated, and made of reworked loessic matrix that includes numerous small quartzite blocks. The laminations of these solifluction deposits are reflect minor fluctuations in deposition, which was probably always under periglacial conditions with sparse vegetation [20]. This deposit may correspond to an accumulation of solifluction lobes, usually developed on 2 to 35° slopes[21]. US-102 is characterized by increased illuviation, highlighting the former laminations (Bt horizon). The observed pedogenesis may be explained by the presence of an ancient and eroded soil, developed on permafrost, during the end of LGM [22], around the Early Bølling, ca. 16, 000 BP. US-102 contains, especially in the upper part of it, most of the azilian artifacts and makes up the archaeological layer. Above these formations, several units of colluvium were laid down (US-104 and US-108). US-104 is a partially preserved colluvium, deposited by runoff, anterior to the late Neolithic recorded in US-108 and strongly pedogenetised (old Bt horizon). Above it, US-108 includes lots of plurimetric quartzite boulders that fell from the overhanging Ordovician bar, and mixed within the colluvial silty-clayey matrix. The boulder rock falls, which are a part of this infilling, are important as they locally protect the former layers from erosion. The lithic artifacts and a radiocarbon date suggest this layer was mostly deposited at the end of the Neolithic. The top unit of the stratigraphic sequence of the rock-shelter, is a strongly disturbed unit (US- 101), made of humic silty-clayey colluvium reworked by recent anthropogenic digging and filling. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 2. Summary cross section of the central area of the rock-shelter. US- 101: Humic horizon on silty-clayey colluvium and modern anthropogenic filling. US-108: Scree of quartzite boulders in silty-clayey colluvium. US-104: Strongly developed colluvium (Bt horizon). US-102: Solifluction layer made of reworked lœss and small cryoclastic quartzite boulders and gravels. US- 103: Lightly reworked lœss (M. Laforge & S. Sorin). https://doi.org/10.1371/journal.pone.0173037.g002 Within US-102 we have discovered an unquestionable archaeological layer attributed to the EA. US-102 is preserved in most areas of the site, and occurs towards the bottom of the stratigraphic sequence. Since we know that the debris flow of US-102 unit was not reworked after the Lateglacial, Azilian populations could have lived on this unit, which is confirmed by the high concentration of artifacts within this layer. Furthermore, the identification of a roof collapse event of large quartzite boulders between the Neolithic and the Azilian favors the preservation of the Azilian-aged soil under the largest blocks. Because the site is located in the Armorican Massif, the acidic soil does not allow for the preservation of organic materials. As for most sites within this region of France, our studies and hypotheses are primarily based on the study of lithic materials. Due to the presence of a regular blade industry produced by soft hammerstone, emblematic early Azilian bipoints (curved back points with two opposed tips), and flat retouched blades, the lithic assemblage can be assuredly attributed to the EA. These reduction techniques and artifacts characterize assemblages from other well-excavated and preserved sites in Europe that date to this time period, including the lower layer of Le Closeau [14], La grotte du Cheval [23], layers 4 sup./3B of Pont d’Ambon [24], layer 4 of Abri Murat [25], layer 3 of area 1 of La Fru [12] and layer 4 of Bois-Ragot [26]. Three radiocarbon dates at Le Rocher de l’Impératrice fall into the GI-1 (Bølling for two of them and the Bølling-Allerød transition for the other) (Table 1) and support this attribution. These radiocarbon dates fit perfectly with other assays for this period in France (Table 2). The Rocher de l’Impératrice assemblage is culturally homogeneous, especially in US-102. Most of the artifacts discovered in the disturbed units of the rockshelter are also related to this Upper Paleolithic techno-complex. Very few Mesolithic artifacts have been discovered and only a small Neolithic assemblage is present in US-108. Although several of the engraved stones were discovered in a disturbed unit of the shelter, the entire corpus can be reasonably attributed to the EA occupation(s). Indeed, the horse-aurochs theme as well as the style of the figures undoubtedly refer to the Paleolithic fine naturalistic art which completely differs from the Neolithic and Mesolithic graphic works currently known in Western Europe [27–29]. There is also no evidence of dates or artifacts related to other Upper Paleolithic period. The Rocher de l’Impératrice is one of the very few EA sites with art but no evidence of a Magdalenian occupation. The geological context and artefact assemblage allows for a discussion of the technical and symbolic changes during this period. PPT PowerPoint slide

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larger image TIFF original image Download: Table 1. Radiocarbon dates of Le Rocher de l’Impératrice. https://doi.org/10.1371/journal.pone.0173037.t001 PPT PowerPoint slide

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larger image TIFF original image Download: Table 2. Radiocarbon dates for the French Early Azilian. https://doi.org/10.1371/journal.pone.0173037.t002 Because the lithic assemblage is limited and artifacts are restricted to the inside of the shelter with little evidence of hearth-related activities (no hearths and few burnt artifacts or charcoal) we suggest this small quartzite shelter was occupied by a small group during the EA (and probably several times by several groups). The very high proportion of retouched tools on the site (42% of the assemblage) along with only scant evidence of lithic production activities (only one core and low proportion of by-products) suggest that people probably arrived equipped with tool kits consisting of blades and prepared cores used to produce small blades designed for the creation of projectile points. Cores used to make these tools were afterwards carried out of the site. These data suggest that the site was occupied for short periods of time for specific tasks. More precisely, the focus on the manufacture of projectile points (presence of preforms and very high frequency of micro-flakes produced during the manufacture of the points) and use (30% of points with impact fractures) suggests use of the rockshelter as a hunting camp. The importance of unretouched and retouched regular blades in the assemblage could also support this hypothesis maybe suggesting butchering activities on the site. The use wear analysis of the lithic assemblage by J. Jacquier is in course and will soon bring important data on this topic. The engraved tablets, however, make this scenario more complex, suggesting not only an economic but also a symbolic function of the site. Moreover, they question the purpose of the graphic production within the economic sphere of these people, especially within their food supply. Was the iconography linked with the hunt, perhaps to ensure its success? Was it strictly symbolic, or a mere past time?

4. Discussion This collection testifies to formal and technical homogeneity, with some particular graphic conventions shared by different figures: the angular and pinched muzzles of the little horse on slab 741B and the horse on fragment 607, and the representation of the coat with a series of short oblique straight lines along the outlines of the horses on slab 741 and the aurochs on slab 317. Because of the obvious stylistic unity of these figures, we consider the corpus as a coherent assemblage in which coexist two formal renderings of the animal, one naturalistic, the other schematic. Even if most of these artifacts were discovered in the disturbed unit of the shelter, the entire corpus of engraved tablets can reasonably be attributed to the Early Azilian occupation(s) of Le Rocher de l’Impératrice as no evidence of occupation prior to the Azilian was found on the site. The 45 engraved stone fragments from Le Rocher de l’Impératrice are the oldest graphic remains in Brittany and prove to be exceptional for the EA. In France, less than a dozen sites have yielded decorated items related to this techno-complex, most of them from uncertain contexts. Among them, only three collections of mobile art can be clearly attributed to this culture: the 82 engraved lithic artifacts of Murat rock-shelter (layers B and D of Lemozi, layer IV of Lorblanchet: [25]), the five flakes with engraved cortex of Le Closeau [14], an engraved pebble of Bois-Ragot (layer 4: [26]). A single parietal art site is attributed to the EA- Gouy cave [23, 46]–on the basis of the lithic industry found at the site; however, no direct link exists so far between the parietal set and the archaeological deposit. In this regard, the collection of Le Rocher de l’Impératrice considerably increases the data. Even if it is difficult to draw general conclusions about the Early Azilian symbolic system from these few sites, and the very restricted corpus for Le Closeau and Le Bois-Ragot, a coherent image of these graphic works still appears: the notable selection of small pebbles and slabs as blanks, and the mostly unifacial sets made of a unique motif or a very small number of superimposed motifs. The iconography combines both geometric themes such as checkered triangles, lines, or beams, and figurations with bestiaries dominated by horses and aurochs (Fig 8). The schematic animals depicted in Gouy cave bear stylized coats in the form of grid patterns or parallel lines reminiscent of the aurochs on tablet 317 [46], together with angular and pinched muzzles for the horses. Murat rock-shelter figures also show two types of formal rendering: schematic representations cohabit with realistically shaped and dynamic animals with simplified internal details (Fig 8). PPT PowerPoint slide

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larger image TIFF original image Download: Fig 8. Engraved mobile art from the Early Azilian (8–11) and the Upper/Final Magdalenian (1–7): 1) Le Morin (P. Laurent in [47]); 2) Villepin (G. Tosello in [48]); 3–4) La Madeleine (G. Tosello in [48]); 5) Limeuil (G. Tosello in [48]); 6) La Mairie cave (P. Paillet in [49]); 7) Rochereil (P. Paillet in [5]); 8–11) Murat rock-shelter (M. Lorblanchet in [25]). https://doi.org/10.1371/journal.pone.0173037.g008 The EA iconography of Le Rocher de l’Impératrice is very similar to the Upper-Final Magdalenian and several elements suggest direct continuity. That is the case of the selected materials to be engraved: pebbles and tablets are also abundantly used in large lithic mobile art assemblages such as Limeuil, Gourdan, Gönnersdorf, La Peña de Estebanvela and Foz do Metal [40, 48, 50–53]. This similarity can also be seen in the technical preference for engraving instead of painting. The compositions associating geometric patterns, figures and unorganized tracings is another common pattern. The themes are also very similar: the geometric register appears to remain rather unchanged with the predominance of chevrons, grids, lines beams, together with triangles and ellipses. As to the figurative register, aurochs and horses also fill the Upper/Final Magdalenian bestiary even if aurochs are not very common. The formal conventions of the animals in Le Rocher de l’Impératrice match well with those documented of the Upper-Final Magdalenian: a realistic rendering with complete bodies, with the two finely reproduced pairs of legs, seen in real perspective, shapely silhouettes, and numerous anatomical details depicting the sensorial organs, the internal volumes and the coat. Macrocephaly of the horses is another strong figurative trend [5, 54]. These formal traits are shared within the whole graphic production of the second half of the Magdalenian in Western Europe, from the Paris Basin with the engraved pebble from Étiolles [55] to the North of Spain (Abauntz: [56]; in others). They are also the ones of some parietal paintings directly dated between 13,500 and 12,500 BP at Niaux [57], La Pasiega C [58], and El Castillo [58]. Some particular Middle-Upper Magdalenian conventions can be more specifically pointed: the depiction of the zygomatic depression (aurochs 317A, horse 741A?), the stylized representation of the coat as a series of short, straight oblique lines stuck to the back line (aurochs on fragment 317, horse 741A) or as a fine hatching filling inside the legs and the belly (horses on tablet 741) [5, 44, 48–49, 51, 59]. A less detailed formal rendering could be argued for the engravings at Le Rocher de l’Impératrice but simplified representations are also found in the Upper-Final Magdalenian together with very naturalistic figures, some turning very schematic, sometimes within the same assemblage (e.g. abri Mège, La Mairie, Le Morin, Limeuil, Laugerie-Basse, Rochereil or La Madeleine–[49, 60]). From these results we suggest continuity in the iconographic tradition between the Upper Magdalenian and the EA, as already suggested by M. Lorblanchet in Murat [25]. The dearth of artistic items from the EA nevertheless limits our estimation of the degree of longevity after the Upper Magdalenian. However, the special valorization of the aurochs as shown by the “shining bull” could indicate some symbolic recoding of the traditional bestiary. Evidence is too scarce at the moment to develop this hypothesis further. We also suggest that the chrono-cultural attribution of some Upper Magdalenian mobile art collections should be reevaluated with the possibility that some may be more recent since many assemblages were actually collected in sites where the Upper Magdalenian layers are generally covered with EA and LA layers (e.g., La Madeleine, Villepin, grotte Richard; [48]; Laugerie-Basse: [61]). However, this continuity is particularly striking with regard to the Southern cultural context of Northern Spain where the Upper-Final Magdalenian lasts until 11,800–11,600 BP whereas the EA develops in France [62]. Thus, two neighboring cultural groups with different domestic and hunting equipment but a common iconography seem to coexist (i.e., in others La Vache, Le Portel, Ekain VIb, Oscura de Ania IIIa, Abauntz 2r, Las Monedas, La Pasiega C–[44, 63–66]). These results provide the first picture of a graphic tradition in the EA clearly distinctive from the LA whose iconography is dominated by painted and engraved abstract patterns on pebbles; however such abstract pebbles could be already present in the EA in Murat rock-shelter (layers B and D of Lemozi, layer IV of Lorblanchet). Similar pebbles in Bois-Ragot (layer 4), Gay rock-shelter and Rochedane [2, 67], are likely from mixed contexts containing EA and LA materials. Where abstract pebbles are found in secure contexts, there is a clear iconographic schism between the EA and LA in regard to 1) a shift in material selection with use only of standardized pebbles, 2) painting as a preferred technique, 3) the explosion of abstract expressions in the shape of repeated simple patterns (points, lines, crosses, chevrons), 4) the correlative scarcity of depiction whether animal or human, and 5) a change in the formal rendering of the figures in favor of geometric schematism. The lines are simplified and rugged (triangular legs without hoof), the bodies are wide and the heads atrophied. Most often, the internal details are missing. The bodies can be blank or filled with patches of long tracings, oblique or horizontal on the flank, vertical in the legs (Murat: [25]). Similar iconographic changes accompany the spread of the classical Azilian in the North of the Iberian peninsula [53, 68]. The data presented here highlight a discrepancy between technical and symbolic changes during the azilianization process. If the graphic corpus of Le Rocher de l’Impératrice testifies to iconographic continuity with the Magdalenian, the lithic assemblage already bears all the Azilian characteristics with especially the exclusive use of soft hammer stones and the exclusive use of axial projectile points to the detriment of backed bladelets. The major transformation of the symbolic system with the development of a geometric expression and the correlative near-abandonment of animal and human figures seems to start later. While the data are still too scarce to determine precisely when a shift in symbolic system begins, those available data suggest the beginning of the Allerød. The move away from Magdalenian and EA iconography probably occurred after the beginning of the LA. This timing is suggested by the discovery of a horse head still bearing the EA formal conventions (arched nose, pinched lip, few details but the mention of the zygomatic depression and the coat represented by series of long vertical lines) engraved on cortex found in layer III.20 at Pincevent dated around 13,600 cal. BP at the beginning of the LA ([69–70]; Fig 9). PPT PowerPoint slide

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larger image TIFF original image Download: Fig 9. Similarities of conventions in the formal rendering of the horse heads from Le Rocher de l'Impératrice and Pincevent (layer III.20) (photo N. Naudinot; tracing D. Baffier in [ Similarities of conventions in the formal rendering of the horse heads from Le Rocher de l'Impératrice and Pincevent (layer III.20) (photo N. Naudinot; tracing D. Baffier in [ 69 ]). https://doi.org/10.1371/journal.pone.0173037.g009 This study underlines a difference in rhythm between technological and symbolic changes of the Magdalenian and EA. Our data suggest a progressive dissolution of the Magdalenian lithic standards while conventions of Magdalenian iconography seem to change later and abruptly by the Allerød. The likely disappearance of animal and human figures in favor of an exclusive abstract expression is a crucial iconographic shift with regards to the other former Upper Palaeolithic societies and to the subsequent final Paleolithic populations in Western Europe. While it is possible that this picture of a clear scission in the symbolic sphere is only caused by the lack of data between EA and LA, the findings at Le Rocher de l’Impératrice suggest that Magdalenian iconography is greatly extend in time. The onset of the Azilian is not a package of changes affecting both the symbolic system and technical equipment. It is essential to understand the origin of this critical evolution in symbolic expression, which may bear important ideological and sociological significance during the Azilian. The simple techniques, motifs, as well as the large residential sites in which the decorated pebbles are generally unearthed would rather indicate common productions of these items in the LA. This marks an important shift from Magdalenian graphic production [62], which emphasizes a complex technical savoir-faire, realism, and a degree of detail in numerous representations that are without any doubt the work of specialists who went through a distinct learning process [71–72]. According to Gonzalez Morales [73], the abandonment of figures for geometric expression would be linked to changes in the techniques used and in the actors, and the three would result from a complete series of global changes in the social organization of graphic production. In parallel, the decrease in savoir-faire can also be identified in the lithic and bone technology of the LA. It is tempting to see these phenomena as a possible development of a common production strategy that minimized the importance of specialists in both graphic and technical activities. These data could suggest a major sociological shift during the Allerød. Changes in mobility patterns, judged by the few data available, suggest a potential increase in residential mobility during the LA [6, 13, 74–76]. This change in mobility is important to consider as the reorganization of activities in time and space may be profoundly linked with these cultural changes. In human cultural evolution, changes in the cultural system do not necessarily affect all elements of material culture at the same time [62, 77]. This is sometimes contrary to the general idea conveyed in archaeological studies. This vision is mostly perpetuated by the nature of the archaeological record as our theories and interpretations are often based on an extremely fragmentary subset of remains from past cultural systems. Sites like Le Rocher de l’Impératrice with remains of various parts of the cultural system allow us to discuss and compare differences in the tempo of cultural change. In this case, the development of Azilian cultural or symbolic acts appear to lag behind major technological adaptations.

Supporting information S1 Table. Engraved tablets database. Captions: L/D: Large and deep engraving; F/S: Fine and superficial engraving; F.D: Fine and deep engraving; W/D: Wide and deep engraving; W/D+Ch: Wide and very deep engraving with champlevé; SPSC: Small patches of sediment crusts; SPSD: Small patches of sediment deposit; SPSDC: Small patches of sediment deposit and crusts; HP: Highly patinated surface; HEE: Highly eroded edges; HPT: Highly patinated tracing; OAA: Other anthropological action; 1: Blue grey; 2: Visible lamination; 3: metallic light grey; 4: light and dark blue; 5: Shiny lamination; 6: Pearlescent pinkish light grey; 7: Matt slate grey; 8: Matt dark blue grey; 9: Grey https://doi.org/10.1371/journal.pone.0173037.s001 (DOCX) S1 Fig. a)Several Raman spectrum obtained on the black pigment in the engraving compared with some obtained on the shale tablet out of engraved areas and without visible black colour. These signatures are constituted by the symmetric stretching of carbon-carbon single bonds (band around 1367 cm-1) and carbon-carbon double bonds (band around 1597 cm-1). Spectra are baseline corrected to remove the fluorescence contribution. Several spectra from the two kind of areas are overlapped to underline reproducibility, and the two vertically shifted for readability. b) Same spectra from both areas overlapped in order to highlight the shapes different between the pigment and the carbonaceous matter from the shale. https://doi.org/10.1371/journal.pone.0173037.s002 (DOCX)

Acknowledgments This work was conducted with the help of the SRA Bretagne (French Ministry of Culture and Communication), the Conseil départemental du Finistère and the municipality of Plougastel-Daoulas. We would like to also thank all the students and volunteers involved in the excavation of Le Rocher de l’Impératrice. We are extremely thankful to Robert L. Kelly (University of Wyoming) and Joseph A.M. Gingerich (Ohio University and The Smithsonian Institution) who helped considerably with the manuscript and François Bon (University of Toulouse II) for his precious advice. Thank you to Marco Peresani (Ferrare University), Patrick Paillet (UMR 7194, Muséum national d’histoire naturelle), Ludovic Mevel (UMR 7041, Arscan) and the other three anonymous reviewers of this paper.

Author Contributions Conceptualization: NN CB. Data curation: NN. Formal analysis: NN CB ML SB CP LBG ITP. Funding acquisition: NN. Investigation: NN MLG. Methodology: NN CB ML SB CP LBG ITP. Project administration: NN. Resources: NN MLG. Supervision: NN. Visualization: NN CB ML. Writing – original draft: NN CB ML CP LBG. Writing – review & editing: NN CB.