A pre-Campanian Ignimbrite techno-cultural shift in the Aurignacian sequence of Grotta di Castelcivita, southern Italy

The Aurignacian is the first European technocomplex assigned to Homo sapiens recognized across a wide geographic extent. Although archaeologists have identified marked chrono-cultural shifts within the Aurignacian mostly by examining the techno-typological variations of stone and osseous tools, unraveling the underlying processes driving these changes remains a significant scientific challenge. Scholars have, for instance, hypothesized that the Campanian Ignimbrite (CI) super-eruption and the climatic deterioration associated with the onset of Heinrich Event 4 had a substantial impact on European foraging groups. The technological shift from the Protoaurignacian to the Early Aurignacian is regarded as an archaeological manifestation of adaptation to changing environments. However, some of the most crucial regions and stratigraphic sequences for testing these scenarios have been overlooked. In this study, we delve into the high-resolution stratigraphic sequence of Grotta di Castelcivita in southern Italy. Here, the Uluzzian is followed by three Aurignacian layers, sealed by the eruptive units of the CI. Employing a comprehensive range of quantitative methods—encompassing attribute analysis, 3D model analysis, and geometric morphometrics—we demonstrate that the key technological feature commonly associated with the Early Aurignacian developed well before the deposition of the CI tephra. Our study provides thus the first direct evidence that the volcanic super-eruption played no role in this cultural process. Furthermore, we show that local paleo-environmental proxies do not correlate with the identified patterns of cultural continuity and discontinuity. Consequently, we propose alternative research paths to explore the role of demography and regional trajectories in the development of the Upper Paleolithic.

www.nature.com/scientificreports/ to hypothesize that the Aurignacian indicates a second, and possibly more successful, wave of Homo sapiens expansion across Europe 11,12 .Some of the most crucial sites for understanding the early stages of the Aurignacian lie to the south of the Alps and along the Italian Peninsula 13,14 .In northern Italy, the onset of the Aurignacian is dated to ~ 43-42 ka cal BP [15][16][17] .Notably, at the sites of Riparo Bombrini and Grotta di Fumane (Fig. 1a), two Homo sapiens deciduous teeth were discovered within the earliest Aurignacian layers.This discovery provides direct evidence of the makers associated with the lithic assemblages.Moving southward, the Aurignacian begins later.Chrono-stratigraphic evidence suggests that foraging groups persisted in the production of Uluzzian industries in southern Italy, at least until ~ 41 ka cal BP 18,19 .
The earliest expression of the Aurignacian in Italy is recognized as the Protoaurignacian (PA) 21 .In terms of lithic technology, the PA is predominantly characterized by the production of slender and straight bladelets from platform cores through direct, marginal percussion 22 .The reduction procedures linked with this core technology frequently result in the creation of larger blanks, such as blades, for shaping and maintaining core convexities.This process hampers the differentiation between blade and bladelet blanks based on metric and shape attributes [23][24][25] .Bladelets are frequently modified on one or both edges using marginal retouching 26 , exemplified by sites like Fumane, where retouched bladelets constitute nearly 90% of the tool category 27 .
The development of the Aurignacian in Italy remains a topic of ongoing debate, as only a limited number of stratified sites offer a clear shift from the PA to the so-called Early Aurignacian (EA) cultural variant, unlike some other regions in Europe 28,29 .The EA represents the most investigated cultural variant of the Aurignacian and is considered the initial expression of the Upper Paleolithic in certain regions, such as the Swabian Jura in southwestern Germany 30 .In Table 1, we present a compilation of the most distinctive techno-typological lithic and osseous markers crucial for tracing the chrono-cultural development in the early phases of the Aurignacian.It is important to note that the observed differences are more subtle than previously assumed and should be viewed as tendencies within a generally uniform technological system 22,31 .
Northern Italy adds complexity to this narrative, as researchers working at Fumane and Bombrini suggest that the PA persisted for a longer duration compared to other European regions 27,32 .Nevertheless, the chronological and archaeological reliability of these findings remains a subject of debate [33][34][35][36] .At Riparo Mochi, a PA-EA shift is indeed reported, although updated technological studies are still pending 17 .Other sites associated with the EA are identified in central Italy, particularly in the Circeo region, exemplified by cave sites like Grotta del Fossellone 37,38 .
Given the substantial number of sites and the extensive Paleolithic research tradition 14 , southern Italy emerges as a compelling case study for a more comprehensive understanding of the development of the Aurignacian in Reported sites: (1-2) Riparo Mochi and Riparo Bombrini, (3) Grotta di Fumane, (4) Grotta La Fabbrica, (5) Grotta Paglicci, (6) Serino, (7) Grotta di Castelcivita, (8) Grotta della Cala.The maps show the paleo-geographic reconstructions of Italy and the Cilento region, taking into account mean sea-level estimations with associated confidence envelopes 20 at about 40,000 BP (− 62 ± 13 m above the current sea level).The map was generated using ArcGIS ® 10.8: (https:// deskt op.arcgis.com/ en/ arcmap/ latest/ get-start ed/ setup/ arcgis-deskt op-system-requi remen ts.htm).Source of the Digital Elevation Model: GMES RDA project (https:// www.eea.europa.eu/ dataand-maps/ data/ eu-dem# tab-origi nalda ta/ eudem_ hlsd_ 3035_ europe).Source of the Bathymetry: EMODNET (https:// emodn et.ec.europa.eu/ en/ bathy metry).Italy, the Uluzzian represents a distinct cultural departure from the preceding Mousterian and stands as one of the most thoroughly studied technocomplexes, owing to its significance in discussions concerning the arrival of Homo sapiens in Italy 7 .In terms of behavior, the Uluzzian is characterized by several distinctive features.These include the widespread use of bipolar technique on anvil to produce flakes and bladelets [72][73][74] , the presence of lunates used in mechanically delivered weapons 75 , the utilization of coloring materials, the production of simple bone tools (e.g., awls), and the use of seashells as personal ornaments.A notable feature is the frequent presence of the tusk shell (i.e., Antalis sp.), regarded by some as a hallmark of the Uluzzian 76 .
At Castelcivita, the Uluzzian is identified in four layers (i.e., upper-rsi, pie, rpi, and rsa").Above rsa'', three layers (rsa', gic, and ars) were classified as PA based on their position in the stratigraphy just below the CI tephra and the presence of a substantial sample of retouched bladelets 46 .Paolo Gambassini's study 46 , based on Laplace typology 21 , highlighted the appearance of a miniaturized retouched bladelet type in the layers following the earliest PA, indicating a possible technological change at the site.In the literature, these layers are sometimes referred to as "Protoaurignacian with micro points" 18,74 .Despite this, the technology employed in producing these bladelets has not yet been examined to determine whether technological continuity or discontinuity exists across the sequence.Geological observations by Giaccio and colleagues 43 suggest that the ca.50 cm of the rsa'-ars sequence Table 1.List of the most distinctive features for identifying Protoaurignacian and Early Aurignacian assemblages.Regional markers are excluded from this compilation, which is based on various review papers 22,31,33,36 .

Protoaurignacian Early Aurignacian
Lithic technology -Frequent use of unidirectional platform cores for long and straight bladelets.
-Blades frequently obtained from bladelets cores, via initialization or maintenance, as well as through simultaneous reduction procedures.
-Regular use of carinated cores for short, but not twisted, bladelets.
-Independent production of blades from unidirectional platform cores, with high regional variability due to variations in raw material availability and quality.
-Bladelets frequently left unretouched, although alternate or inverse retouching occasionally applied.
-Endscrapers as the dominant tool type.
Osseous technology -Antler points seldom attested and lack modifications at the base.
-Antler points with a split at the basal end of the tool found at certain sites.
at Castelcivita accumulated over just a few centuries, commencing at the end of the Uluzzian 18 .Consequently, the site offers an exceptional snapshot of the earliest stages of the Aurignacian before the CI super-eruption.
In this paper, we conduct a comprehensive quantitative investigation of all Aurignacian layers at Castelcivita (rsa', gic, and ars) and examine the hypothesis that no significant technological changes can be discerned prior to the CI super-eruption.Our approach involves a techno-typological study focused on reconstructing the production methods of laminar blanks, contrasting the results against the defining features of the PA and EA technological systems.Our findings reveal that technological changes at the stratigraphic transition between rsa' and gic align with a tendency towards the shift to the EA, as already documented in western European sites.Importantly, the process leading to the reliance upon carinated technology at Castelcivita occurred well before the CI super-eruption and the H4, indicating that there is no direct correlation between cold and arid conditions and this technological shift.This study further underscores the distinct regional character of the Castelcivita assemblages, emphasizing the challenges involved in studying Upper Paleolithic population dynamics.Given the regional specificity, we advocate for caution when establishing causal connections between cultural development and environmental fluctuations.www.nature.com/scientificreports/Moreover, from a methodological standpoint, we introduce an approach to lithic analysis that combines traditional technological methods with 3D model analysis, 2D geometric morphometrics, and Open Science practices.Notably, all data manipulation and statistical procedures were carried out within the R programming environment 77,78 and are made available on Zenodo alongside the datasets required to reproduce our findings 79 .Similarly, 3D models of cores and other noteworthy tools can be accessed in an open-access repository on Zenodo 80 .

Blank production
The most striking feature marking the transition from the Uluzzian to the PA at Castelcivita is the sharp increase in bladelet technologies.Flakes, however, were still produced in all studied assemblages.While not the primary focus of this paper, a description of flake production is included in the Supplementary Information.Notably, the most significant difference identified across the sequence is the decline in the number of bipolar cores in gic-ars compared to rsa' (Supplementary Fig. S2).It is worth noting that bipolar technology is a defining feature of the Uluzzian assemblages at Castelcivita, where it accounts for up to 50% of the lithic production 46,72 .This frequency drops considerably in rsa'.
Table 3 presents all cores bearing evidence of blade and bladelet production, which were discarded during the formation of the rsa'-ars sequence, classified following the criteria outlined by Falcucci and Peresani 82 .The analysis of cores and blanks associated with the initialization and maintenance of core convexities reveals consistent raw material selection strategies and decortication procedures throughout the sequence.In layer rsa', the numerous crested blanks demonstrate that PA knappers frequently utilized core cresting to shape the convexities of bladelet cores (Supplementary Information).Cresting was a commonly employed method to maintain platform cores in the PA, as evidenced by findings from various sites 22,83,84 .The frequency of crested blanks drops in layer gic due to the diminished use of platform cores and the increased prevalence of carinated cores (as discussed below).Although crests could be used to initiate blank production on carinated cores, the knapping progression in these cores is known to more effectively auto-maintain the lateral convexities, thus reducing the need for this technical solution 85 .
The analysis of crested and fully cortical blanks suggests that blade production was not very common, likely due to constraints related to the size and quality of available raw materials.Exhausted cores provide more insights into the technological variability identified across the sequence (Fig. 4).In rsa', core technology displays a wide range of reduction strategies, with cores oriented according to the longitudinal axis being the most frequent (Fig. 4h-o).Notably, the semi-circumferential strategy is the most common, while narrow-sided and burin cores are less frequent.The high frequency of multi-platform strategies underscores the frequent rotation of cores to fully exploit available raw material volumes.
Intriguingly, carinated technology, the hallmark of the EA, becomes strikingly dominant in gic and ars (see Fig. 4b-d, and g).When considering all cores with evidence of carinated technology (i.e., carinated cores, carinated core shatters, initial carinated cores, multi-platform cores with at least one carinated reduction sequence; see Supplementary Information), the frequency in gic (n = 37; 64%) and ars (n = 4; 57%) is in clear contrast to rsa' (n = 14; 26%).The technological configuration of carinated cores is however largely consistent across the analyzed layers.Flaking surfaces are primarily wide, striking platforms are plain, and flaking is unidirectional.The significant difference lies in the utilization of shorter flaking surfaces in the upper part of the sequence (Supplementary Fig. S4).Maintenance blanks associated with carinated technology 85,86 are more prevalent in the upper layers.However, their presence and metric characteristics confirm that carinated technology was also used in rsa' (Supplementary Information).Overall, bladelets are the primary production focus throughout the sequence, as shown in Table 4. Analysis of discarded cores and maintenance blanks suggests that independent blade production occurred mainly in gic, while simultaneous blade-bladelet production is more prominent in rsa' (Supplementary Information).
We measured the last successful blade or bladelet removals on cores and plotted these measurements along with the length and width values of all complete blades and bladelets in the dataset (Fig. 5).In general, the last removals on cores are predominantly classifiable as bladelets, with only a few scars in gic (n = 4) attributable to blades.The gic scatterplot reveals a notable agreement between the size of the last removals on cores and the complete blades and bladelets.Additionally, there is a noticeable reduction in overlap between the sizes of bladelets and blades at the stratigraphic transition from rsa' to gic.In rsa', numerous bladelet negatives overlap in length with complete blades, highlighting how the reduction of platform cores resulted in the concurrent production of both blades and bladelets, as commonly observed in the PA 24 .Based on the presented data, layer gic demonstrates a substantial increase in the independent production of bladelets, aligning with the increased reliance on carinated core technology (see also Supplementary Information).

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We conducted a Principal Component Analysis (PCA) on five selected quantitative variables measured on blade and bladelet cores to better frame the variability of core types and the technological differences across the sequence.Results are reported in the associated R script and visualized in Fig. 6 and Supplementary Fig. S6.The first three PCs collectively account for approximately 88% of the overall variance, with eigenvalues ranging from 0.99 to 2.4 (Fig. 6a).The graph in Fig. 6b illustrates the strong correlation among shape variables, while the mean striking angle demonstrates an inverse correlation with core volume.The least explanatory variables in the first two principal components are the mean striking angle and the length-to-width ratio of the flaking surface, whereas the length of the flaking surface stands out as the most significant quantitative variable.The qualitative variable "core type" primarily explains the variability observed in the first component, largely distinguishing carinated cores from all other platform cores.Not surprisingly, the variance along the first PC is strongly influenced by the layer of provenience, as gic cores are predominantly associated with the carinated strategy (Fig. 6c, d).The significance of these findings lies in their quantitative validation of our core classification, effectively capturing the prominent morphological variability and further emphasizing the clear distinction between gic and rsa' .
The differences identified across the sequence are closely related to the intended production goals.The morphometric analysis of blades and bladelets, detailed in the Supplementary Information, further reinforces the technological shift between rsa' and gic-ars.While most of the compared discrete and metric attributes recorded on blades are quite similar across the sequence, a noticeable reduction in the length of complete blades is observed in gic.Conversely to blades, bladelets exhibit more significant variations.Firstly, attributes associated with knapping techniques suggest the use of more marginal percussion in gic.In profile view, bladelets from gic are straighter and less frequently twisted.The knapping progression in gic is often unidirectional convergent.Finally, bladelets recovered in gic and ars are smaller in terms of length, width, and thickness.

Tool analysis
The classification of tool types reveals significant variations (Table 5 & Supplementary Figs.S13-S15).Retouched bladelets are consistently the most numerous tool type throughout the stratigraphic sequence, with the highest frequency in gic.Notably, the number of endscrapers, many of which can be further classified as carinated and associated with bladelet production, clearly increases in gic-ars.Nosed endscrapers, either flat-or thick-nosed (Supplementary Fig. S14b, d) are rare.Burins are consistently less frequent than endscrapers, with the sole exception being in ars; however, its small sample size requires caution.In some cases, burins were classified as bladelet cores, being either carinated (e.g., Supplementary Fig. S15) or displaying multiple bladelet negatives.The latter exhibit a flaking surface oriented along the narrow, longitudinal side of the blank (e.g., Supplementary Fig. S13a).From a typological perspective, the two carinated burins from rsa' can be further classified as busked (Supplementary Fig. S13b) and Vachons (Fig. 4l) burins due to the presence of a distal notch in the former, and the extension of the bladelet negatives along the ventral face in the latter.These burins display the detachment of rather short and curved bladelets.Several flakes and blades with lateral retouch were also identified, especially in Table 3. Core types associated with the production of blades and bladelets.The classification is based on Falcucci and Peresani 82 , which considers the location and orientation of the flaking surface in relation to the striking platform/s.The table does not include tested cores (n = 2) as the objective of the production could not be assessed.The category of carinated burins is subsumed under the broader carinated category (see the tool list for a breakdown).Rounded percentages are given in brackets.Table 2. Quantification of the studied assemblages, categorized according to the lithic classes and their layer of provenience.The noticeable variations in the frequency of lithic categories are attributed to differences in the excavated area for each layer, technological and typological variability across the sequence, as well as the greater number of bipolar cores in rsa' (refer to Supplementary Information).The category "core-tool" includes artifacts involved in the production of bladelets (e.g., carinated endscrapers and burin cores) that can also be classified as tools following a typological approach 81 .We have kept these artifacts separate from the core list to facilitate inter-site comparisons.Percentages are provided in brackets.the lowermost layer.Blades are modified with direct retouch, with the exception of one blade with inverse retouch from rsa'.In this layer, three blades display direct unilateral stepped retouch (e.g., Supplementary Fig. S13f), reminiscent of the so-called Aurignacian retouch 87 .The Aurignacian retouch is also a characteristic feature of a few flakes at Castelcivita.On the other hand, several flakes display very slight and localized edge modifications.It is worth noting that we did not include many of the so-called denticulated flakes that are listed in Gambassini 46 .
Many of the edge traces on these flakes are discontinuous, irregular, and alternating, which likely reflect the presence of taphonomic and trampling scars 88,89 .Overall, when tools are sorted according to blank type flakes are the second most frequently used blanks, following bladelets (Table S30).Regarding blank technology, tools are primarily made from blanks produced during the optimal production phase (Table S31).

Retouched bladelets
A total of 328 retouched bladelets were recovered from the studied layers, with the highest number found in gic (Supplementary Information).Castelcivita has provided an exceptional number of complete retouched bladelets (Fig. 7 and Supplementary Figs.S14-S15), especially in layer gic, representing one of the highest proportions in the Aurignacian 26 .A notable difference between layers is the choice of retouching techniques (Fig. 8a and Supplementary Table S35).In layer rsa', inverse retouch is the predominant technique, followed by alternate and direct retouching in nearly equal proportions.This pattern shifts significantly in gic, where bladelets are almost exclusively modified using direct retouch.In gic, the direct retouch affects more often both edges of the bladelets (Supplementary Table S36).Many of these artifacts were classified as micro-points by Gambassini 46 , who correctly emphasized their uniqueness in the context of the Italian and, more broadly, European Aurignacian.In terms of metrics, retouched bladelets from gic are smaller in all linear dimensions (Fig. 8b and Supplementary Fig. S16), although variation within this pattern exists (see below).

2DGM analysis
To further explore outline shape variability among bladelets and its relationship with size, we conducted Elliptic Fourier Analysis (EFA) on the 2D outlines of all complete bladelets, both retouched and unretouched (n = 841).The PCA on the Elliptic Fourier descriptors reveals significant variance across the study sample.The first four PCs account for 90% of the total variance (Supplementary Fig. S17).PC1 mainly describes elongation, with blanks Table 4. Classification of blade and bladelet cores according to the objective of production identified at the time of discard.Initial cores are not included in this list as scars on initial cores are often related to core shaping operations 22 .Rounded percentages are given in brackets.on the negative axis being stouter.A Spearman correlation test indicates that PC1 is primarily influenced by variations in the length of the blanks (r 2 = 0.56, p < 0.01; Supplementary Fig. S18).PC2 captures distal symmetry, while PC3 and PC4 relate to the convergence or divergence of the base and apex (Fig. 9a).The PERMANOVA test rejects the hypothesis that the means of all groups are equal (F = 19.836,p < 0.01).
The Pairwise Euclidean distances and the mean shapes of artifacts categorized by class (i.e., tool or blank) and retouch position provide additional information on the identified variability (Supplementary Fig. S19).First, non-modified bladelets from gic are statistically different from the same group in rsa'.Second, the main expectation of the comparisons with the tools is that retouched bladelets are more elongated due to edge modifications affecting the length-to-width ratio.This pattern was well demonstrated through a 3DGM analysis on a sample of PA bladelets from northern Italy 90 .Overall, this expectation is met across all mean shape comparisons, with the exception of the comparison between non-modified bladelets and bladelets with direct retouch from rsa'.The     PCA biplot in Fig. 9c and the PC1 boxplots in Fig. 9b also confirm this discrepancy as the bladelets with direct retouch plot more towards the negative axis of PC1, instead of the opposite, as in all other cases.

Contextualizing the lithic assemblages from layers rsa', gic, and ars
Castelcivita contains one of the most critical sequences for tracking the shift towards the EA cultural variant in southern Italy.The sedimentary complex includes three Aurignacian layers that accumulated within a relatively short timeframe, estimated to be in the order of a few hundred years, just before being sealed by the CI tephra.This eruptive event provides us with an exceptionally well-dated and stratigraphically robust snapshot of the ongoing cultural processes.
In this study, we tested the hypothesis that the PA was a relatively stable technological system prior to the CI super-eruption 44 by employing a varied analytical approach.Significantly, we identified a notable technocultural shift at the stratigraphic transition between layers rsa' and gic, prompting us to reject the initial working hypothesis.From a lithic technological standpoint, the gic assemblage is characterized by the use of carinated technology to produce miniaturized bladelets, which aligns well with the most remarkable trait of the EA, as extensively documented across western Europe 28,30,33,36 .While the CI super-eruption might have led to additional modifications in the subsistence systems of foragers settled in the region, this finding emphasizes that the shift was not influenced by this geological event.Furthermore, it compellingly demonstrates that technological changes occurred within a relatively short timeframe across a broad geographic area, encompassing at least western and southern Europe.
The lithic assemblage retrieved from the lowermost layer rsa' is largely comparable with other PA assemblages excavated throughout Italy.The techno-typological similarities are particularly evident in the frequent production of bladelets with sub-parallel edges from platform cores (i.e., cores oriented along the longitudinal axis of the raw material blank) and a preference for the use of inverse retouching.In particular, these characteristics have been well-documented at PA sites along the Tyrrhenian coast of Italy, including Grotta La Fabbrica 91 , Mochi 92 , and Bombrini 93 .While there are evident similarities, techno-typological connections are less pronounced with the early PA assemblages from Fumane in northeastern Italy 94 .Notably, the lowermost PA stratigraphic unit at Fumane (i.e., A2) site exhibits a more distinct focus on isolating narrow and convergent flaking surfaces to produce pointed bladelets 22,82 , which were modified through a varied range of retouching techniques 26,90 .The observed similarities among Tyrrhenian sites, in comparison to Adriatic Italy, may suggest that foragers settled in this area and/or their ideas traversed more frequently the north-to-south axis along the Tyrrhenian coastline.This geographic patterning within Italy is worthy of future examination, as it seems to align with data available from other Upper Paleolithic periods, such as the middle Gravettian 13,14,95,96 .
The available chronological framework supports a north-to-south terrestrial diffusion route of the PA 97 .Notably, the oldest PA occupations at Mochi on the Ligurian coast coincide with the modeled age for the onset of the Uluzzian at Castelcivita 16,18 .The Uluzzian is currently attributed to Homo sapiens 7,19 , and this fragmented cultural landscape suggests that complex biocultural processes were ongoing between at least 44 and 40 ka.Although this study did not directly address the transition from the Uluzzian to the PA, we are inclined to describe the beginning of the PA at Castelcivita as a rather abrupt event.The sharp increase in bladelet production, primarily achieved through direct freehand knapping, contrasts sharply with the frequent production of flakes and bladelets from bipolar cores in the preceding Uluzzian layers 72,73 .However, it is worth noting that a few carinated cores and retouched bladelets have also been described in these layers 46 .On the other hand, the occurrence of bipolar cores in rsa', which steadily decreases towards the upper layers of the sequence, does not constitute solid evidence for discussing cultural continuity.Geologically, rsa'' and rsa' could not be separated during fieldwork due to their sedimentological similarity and the presence of thin sterile layers only in some areas of the excavation.Moreover, bipolar technology is a common feature throughout the European Upper Paleolithic 98 , particularly in southern Italy 14 .Future research will be designed to investigate this aspect more comprehensively by comparing the rsa'' and rsa' assemblages through a quantitative and multi-disciplinary approach.

On the absence of correlation between environmental proxies and techno-cultural changes
The most notable finding of this study is the identification of a rapid techno-cultural change occurring at the stratigraphic transition between rsa' and gic.However, instead of being an abrupt technological shift with no links with the preceding layer rsa', the results of our technological study suggest that the defining features of the gic assemblage developed within a clear PA technological background, probably as a result of a combination of cultural transmission as well as innovation processes 99 .When quantitatively comparing rsa' and gic-ars, we found technological similarities across different hierarchical categories 100 of lithic production referring to all phases of the core reduction sequence.In this framework, we argue that the use of carinated technology, beginning already in rsa' and becoming predominant in gic, is particularly relevant.The process towards a more independent production of bladelets within the Aurignacian technocomplex is thus to be intended as progressive and bearing a chronological component.For instance, the earliest PA assemblages in northern Italy seldom report the presence of carinated cores 22,93 , unlike the rsa' assemblage at Castelcivita.In western Europe, the transition from the PA to the EA is also not abrupt.Particularly, the presence of carinated technology steadily increases starting from the earliest PA assemblages at sites such as Isturitz, La Viña, Labeko Koba, and Les Cottés 84,[101][102][103] .
Overall, our study shows that the cultural processes leading to the EA in southern Italy were already in motion before the CI super-eruption and were not influenced by the alternation of cold and temperate cycles.This observation shows how finding a direct causality between environmental variations and cultural change is extremely challenging when looking at a single site.Considering the sedimentological, anthracological, and archaeozoological evidence available at Castelcivita, we find that cold and arid conditions are more closely linked www.nature.com/scientificreports/ to rsa', which contradicts the view of the PA as a technocomplex adapted to warmer conditions 64 .Although further studies are needed, we are inclined towards associating the late Uluzzian and the PA with the short cold stadial GS 9/10 identified in the NGRIP2 oxygen isotope curve [104][105][106] .In this context, gic would be linked to the interstadial GI9, while ars, where a new cold phase was detected (see Supplementary Information), to the onset of H4.Notably, the most pronounced cultural shift at the site coincides with the formation of layer gic, marked by a significant presence of arboreal vegetation around the cave.The weak correlation of climatic events to cultural change is further illustrated by the absence of a marked environmental shift during the transition from the late Uluzzian to the PA, as well as by the clear climatic shift identified between layers gic and ars, which are in turn archaeologically indistinguishable.Additionally, it is noteworthy that the impact of H4 in Italy may have been less substantial compared to European regions north of the Alps 107 .For instance, the analysis of a stalagmite from Apulia suggests that southern Italy did not undergo dramatic climate oscillations with the onset of H4 108 .This contrasts with southwestern France, where H4 had a major impact on the environment, establishing a cold steppe dominated by reindeer 109 .

Exploring alternative scenarios and mapping future research trajectories
The distinctive features observed in the gic-ars layers at Castelcivita have opened avenues for future scientific exploration.Remarkably, the pronounced regional signal characterizing these assemblages sets them apart from other sites across Europe assigned to the EA.Castelcivita stands out as the sole site where carinated technology is associated with the frequent modification of bladelets through direct marginal retouching, a virtually unknown trait in the EA from both Central and Western Europe 28,30,36 .Although retouched bladelets are commonly associated with the PA, it is crucial to highlight that the tools in gic-ars are rarely assignable to the larger and straighter Dufour subtype Dufour bladelets 81 , which are typically modified through alternate or inverse retouching 26,81 .Notably, bladelets with marginal retouching remain a consistent feature of the Italian Aurignacian throughout its entire temporal range.Prominent examples include the sequences of Fumane and Paglicci, which extend to approximately 36 ka cal BP 15,27 and 33 ka cal BP 43,110 , respectively.The miniaturized retouched bladelets from layer gic stand out as unique within the Aurignacian context, as noted in the previous typological study 46 .The 2DGM assessment confirmed that their shape is influenced by the utilization of carinated technology, resulting in the production of less elongated bladelets (see PC1 in Fig. 9) compared to the slender bladelets resulting from the platform core technology characteristic of the PA 86 .The function or functions of these bladelets remain unclear, prompting planned functional studies to evaluate whether they were hafted into multi-component hunting tools.In layer rsa', only a few miniaturized bladelets with direct retouch were identified.Several factors, including the absence of a sedimentary hiatus between the two layers, the complex formation processes typical of cave sites 111,112 , and the challenges in establishing a straightforward correlation between field layers and archaeological diachronic changes 113 may have contributed to this outcome.However, it is crucial to note that the occurrence of post-depositional events at the site is limited.The overall integrity of the studied assemblages is robustly supported by the marked variations observed in lithic, faunal, and sedimentological contents.
Differences between the gic-ars layers and other EA assemblages across Europe extend beyond lithic artifacts to include osseous artifacts and personal ornaments.At Castelcivita, there is limited evidence for the use of bone tools in the examined layers.Only an awl made from a roe deer metapodial is described from the excavations led by Gambassini of layer gic 46 .Conversely, no bone tools are yet described from layers rsa' and ars 76 .Split-based antler points 114,115 have not been recovered at Castelcivita.Available data suggests that the split-based points recovered across Italy are generally dated after the CI super-eruption 116 , indicating that this tool type spread south of the Alps in a subsequent phase of the EA 27 .
Unlike other Aurignacian sites in northern Italy and beyond 76,117 , foragers visiting Castelcivita exclusively utilized seashells as personal ornaments (Fig. 10), with no evidence of other raw materials such as teeth, steatite, or bone being used.The most common seashell species is Homalopoma sanguineum, followed by Glycymeris sp. and Pecten jacobaeus 118 .The majority of these artifacts were uncovered during the recent and ongoing archaeological excavations at the site.In layer gic, the frequency of seashells is notably higher compared to rsa', prompting future studies to explore the potential correlation between the site's use and variations in symbolic artifacts.It is important to note that the exclusive use of seashells at Castelcivita does not correlate with chronological proxies, as it is consistent across southern Italian sites from different Aurignacian phases 76 .For instance, at the site of Cala, which techno-typologically aligns with the EA and is dated to after the CI super-eruption, only seashells were recovered 119 .
Considering these diverse lines of evidence, it appears that EA-like assemblages in Italy are culturally less homogeneous than the preceding PA, revealing intricate processes of regionalization stemming from a shared basal adaptation 31 common to all Aurignacian foraging groups.In this framework, the predominant interregional cultural trend visible in the Aurignacian indicates an emergent tendency 120 toward the independence of bladelet production 121 .Conversely, the adoption of carinated technology did not coincide with the synchronous adoption of other cultural traits in the realm of personal ornaments and bone tools.This observation emphasizes that the PA-EA technological shift did not entail significant processes of population turnover or a high degree of population interconnectivity 122 .The scenario proposed by Anderson and colleagues 123 aligns well with this context.The authors view the PA as a pioneering-though not the earliest according to recent findings-phase of Homo sapiens dispersal across Europe, followed by a period of geographic stabilization and the emergence of more distinct regional variants.This reconstruction not only elucidates the delayed onset of the PA in southern Italy but also addresses the significant regional variability observed when comparing different geographic regions of Europe 124 .
Future research should delve deeper into investigating the role of varying demographic patterns in triggering regional cultural changes 125 , as well as the extent of cultural transmission processes at different geographic scales, contributing to the roughly contemporaneous technological shifts identified by archaeologists.Testing null models of isolation-by-distance 126 , for instance, could shed light on the processes behind the regionalization of the gic-ars assemblages when correlated with different demographic simulations and varying degrees of population interconnectivity.It is noteworthy that Castelcivita is positioned at the southern end of the Aurignacian geographic distribution.The distance from other core areas might have influenced the degree of network connectivity among foraging groups settled in the region.Modeling paleo-demography in the Paleolithic poses a considerable challenge, but scholars have been able to demonstrate a strong correlation between population size, network connectivity, and artifact diversity 127 .In this context, we argue that the local development of the miniaturized retouched bladelet type suggests the existence of a local population of sufficient size to initiate innovation and vertical transmission processes that endured long enough to become archaeologically visible.
Another research question deserving exploration concerns the processes underlying the success of carinated technology during the Aurignacian.The gradual replacement of platform cores by carinated cores may be linked to the mobility of foraging groups 121 .Carinated technology allows for the production of standardized bladelets with minimal raw material loss and fewer initialization and maintenance operations compared to platform cores 85,86 , offering a generalized advantage effective in various geological and environmental conditions.Despite raw material selection and transport remaining relatively stable at Castelcivita, the gic-ars assemblages are characterized by a marked miniaturization 128 across all components of lithic technology.This strategy might have resulted in a more economical use of raw materials 129 .In Italy, carinated technology is more markedly associated with regions where foragers relied on low-quality raw materials and/or small-sized pebbles 38,119,130 , suggesting that inter-regional differences in the frequency of carinated cores may also be influenced by the quality and abundance of raw materials.Delving into this research question may also help explain why, in certain regions such as northern Italy, the PA-EA shift is either not evident 27,32 or occurs later 16,17 than at Castelcivita.This discussion, however, should be deferred until new dating frameworks and comprehensive assessments of the integrity of lithic assemblages are thoroughly addressed for all sites.
Planned research in the context of southern Italy will help determine whether the regional signal observed in layers gic-ars at Castelcivita persisted throughout the entire EA duration or if certain elements, such as the miniaturized retouched bladelets, represented short-lived innovations.Two significant candidates for addressing this question are the sites of Cala and Paglicci, both of which feature a stratigraphic sequence that postdates the CI super-eruption.The combined study of these sites will also allow for an assessment of whether and at which point in time cultural transmission processes facilitated the spread of split-based antler points to these southern regions.Confirming this step-like development process would ultimately support our expectation that the shift to the EA did not involve the uptake of the complete behavioral package from its emergence and that underlying demographic dynamics influenced the degree of innovation and transmission mechanisms.

Concluding remarks
In conclusion, our study emphasizes the need for future research to move beyond monocausal explanations of cultural change, providing new high-resolution data on neglected regions of Europe to better contextualize the development of the Aurignacian.The stratigraphic sequence of Grotta di Castelcivita elucidates the reasons behind the success of the Aurignacian across a broad geographic and temporal spectrum compared to the earlier, more geographically constrained Early Upper Paleolithic technocomplexes.Furthermore, it demonstrates the challenges of investigating cultural transitions at different spatial and temporal scales.The rapid technological shift detected at the site does not neatly align with, and may poorly correlate to, patterns of continuity and discontinuity across other archaeological and environmental factors.Separating the emergent trend that leads to the development of the EA and the adaptation of foraging groups to local settings will require the design of interdisciplinary studies and the expansion of archaeological investigations to nearby sites, fully appreciating the regional signal of the Aurignacian in southern Italy and its long-term development.As rigorously discussed by S. Kuhn, "[…] local and global may have quite different dynamics and require quite different kinds of explanations" 120 .By delving into this research path, a more complex picture of the social organization of human groups in the Upper Paleolithic will emerge.

Attribute analysis and reduction sequence analysis
In this study, we have adopted a comprehensive approach, smoothly integrating various methods to analyze lithic assemblages.Our main focus has been on the production of blades and bladelets across the Aurignacian sequence at Castelcivita.We combined attribute analysis 100,131,132 with reduction sequence analysis [133][134][135][136] following the framework set by several other studies 22,27,84,[137][138][139] .This combined approach allowed us to record and analyze a wide array of discrete and metric attributes on individual lithic artifacts, facilitating the reconstruction of core reduction sequences and enabling comparisons between assemblages.The classification of raw materials was conducted based on macroscopically observable surface features and, when applicable, the type of cortex 132 .Cores were classified based on the specific production objective and the configuration of the striking platform(s) in relation to the flaking surface(s).The primary classification followed Conard and colleagues 140 , while further sub-classifications were applied to platform blade and bladelet cores, following the system proposed by Falcucci and Peresani 82 .The classification and technological descriptions of carinated cores were based on the comprehensive works presented in Le Brun-Ricalens and colleagues 141 and the pivotal research of Bon 23 .All laminar cores were measured along their technological axis, following the method outlined by Lombao and colleagues 24 .This implies that the length was measured along the axis of the flaking surface.Consequently, the maximum linear dimensions may differ from the technological dimensions, especially in the case of carinated cores.For bipolar cores, we included all artifacts displaying clear traces of the bipolar technique on anvil, following archaeological and experimental studies 72,73,98,142,143 .We excluded from this category those blanks that exhibited only minor evidence of the bipolar technique, such as short and hinged scars covering a small portion of the artifact.Instead, these were classified as scaled pieces and included in the tool category.Cortex coverage, on both cores and tools, was assessed using five categories (0%, 1-33%, 33-66%, 66-99%, and 100%), enabling comparisons between layers.
For tool typologies, we employed a revised and simplified version of some of the most widely used Upper Paleolithic typologies for classifying tools, drawing from the works of de Sonneville-Bordes 87 and Demars and Laurent 81 .Carinated cores that could also be categorized as endscrapers or burins, depending on the location of the flaking surface, along with burin cores, were additionally classified as tools.Burins were classified as cores when exhibiting multiple bladelet negatives oriented along the longitudinal axis of the blank and featuring a prepared plain striking platform.This approach allowed us to draw comparisons and identify similarities with other previously published Aurignacian assemblages.
Blades and bladelets were categorized based on the metric boundary established by Tixier 144 , defining a bladelet as a laminar blank with a width value below 12 mm.While we acknowledge that this size cut-off is a simplification used for inter-site comparisons, it efficiently captures the essential aspects of Aurignacian lithic production and modification 25 .It is important to note that blades and bladelets are typically defined as blanks with a length at least twice their maximum width.However, it became apparent during the initial scrutiny of materials that this definition could not be rigidly applied at Castelcivita.Several small, regular, and standardized blanks had a length-to-width ratio just slightly below 2. These artifacts closely resembled bladelets produced from carinated cores 85,86 .To avoid adding unnecessary complexity to our results, we chose to classify these artifacts as bladelets, while keeping an additional sub-classification (i.e., flakelets) in the dataset.
The recorded discrete and metric attributes provided us with valuable insights into the knapping technique, the technological organization of stone tool production, and the metric variations within and among assemblages.For recording metric attributes, we utilized a plastic digital caliper which had a precision of 0.2 mm and a resolution of 0.1 mm.A range of discrete attributes was documented on individual lithics to describe the direction and orientation of removals, the shape of platforms and the presence of butts and lips, the profile curvature and twisting of blanks in profile view, and the morphologies of the blanks and distal ends in dorsal view.Retouched tools were excluded from both the metric analysis and the quantification of blank outline and distal end morphologies.Likewise, fragmented blanks were not considered in the morphometric analysis.Statistical assessments of size variability were performed using non-parametric tests such as Wilcoxon and Kruskall-Wallis.To minimize the risk of type 1 errors, we applied the Holm-Bonferroni sequential correction 145 .Statistical analysis was performed on discrete attributes using Pearson's chi-squared or Fisher's exact tests.Fisher's exact test was chosen over Pearson's test when the total number of available observations was below 1,000, aiming to minimize the risk of violating the assumptions of the test.

3D scanning and multivariate analysis of cores
We used an Artec Space Spider (Artec Inc., Luxembourg) to create 3D meshes of all discarded cores at the site, as well as numerous retouched tools, complete blades, and other blanks important for reconstructing the core reduction sequence.In addition to obtaining quantitative data, our objective was to establish an extensive repository of the Aurignacian lithics from Castelcivita.This repository is currently accessible on Zenodo under CC-BY-4.0 80.Besides the standard metric (e.g., linear dimensions, length, and width of last removals) and

2D geometric morphometrics
Quantifying discrete attributes related to the shape of blanks can be challenging as they often rely on descriptors that are subjective and influenced by the analyst's experience and research background 153 .Various studies in the field of geometric morphometrics (GM) have shown that shape analysis is a crucial component for exploring lithic technological variability and understanding design space constraints in retouched tools 25,[154][155][156][157][158][159][160] .To enhance the objectivity of this study, we chose to employ Elliptic Fourier Analysis (EFA) 161 on both unmodified and retouched bladelets.EFA has been widely used in the analysis of 2D shapes of lithic artifacts, both in dorsal view 155,157,158,162,163 and in cross-section 90,164 .To conduct this analysis, we took high-resolution photos of all complete bladelets using a digital camera.We then extracted the artifacts' outlines using the open-source software DiaOutline 165 , which allows for the automatic extraction of outlines from closed shapes and the export of 2D coordinates in .txtformat.Bladelets from ars were not included in this study due to the limited number of complete artifacts, particularly tools, retrieved from this layer.We imported the raw coordinate data into R for the 2DGM analysis, using the Momocs package 166 .Before performing EFA, we centered, scaled, and rotated the outlines.EFA was conducted using the harmonics that captured 99.9% of the cumulative harmonic power, which equated to 23 harmonics.This analysis allowed us to investigate the mean shape of bladelets across the different layers and to run a PCA on the harmonic coefficients to assess shape differences.All raw outlines, R script, and generated datasets are available for download in the associated research compendium.To explore the mean shape variability between gic and rsa', as well as across different groups of tools, we employed a non-parametric MANOVA (i.e., PERMANOVA).We conducted the test using 10,000 repetitions in the vegan R package 167 following Matzig and colleagues 155 .We then utilized the pairwiseAdonis package 168 to calculate pairwise distances using Euclidean distance.For the PERMANOVA, we included only the principal components that accounted for 95% of the explained variance, which amounted to 8 components.Due to sample size, we combined bladelets with inverse and alternate retouch into a single group to allow for a more accurate comparison after confirming the absence of differences between the two retouch types.

R programming and reproducibility
We performed data manipulation, visualization, and statistical analysis in R v.4.3.1 78 and RStudio 77 , using several packages for statistical analysis.To enhance the reproducibility of this study, we created a research compendium that comprises all datasets and scripts.This compendium includes detailed explanations of the steps required to execute and reproduce the analyses, and it can be accessed through Zenodo 79 .We utilized the renv package 169 to establish a reproducible environment, enabling the reuse of our code and workflow.The Supplementary Information html file associated with this paper was generated in R Markdown 170 .In addition to the packages mentioned in the previous sections, we utilized the Tidyverse packages for data manipulation and visualization 171 , janitor for constructing frequency tables 172 , and Rstatix for univariate statistics 173 .

Figure 2 .
Figure 2. Grotta di Castelcivita, showcasing the cave entrance (a) alongside the excavation trench of the Uluzzian and Aurignacian layers (b).Photo a credited to A. Ronchitelli, and photo b credited to P. Gambassini.Both photos were edited by S. Ricci.

Figure 3 .
Figure 3. (a) Stratigraphic sequence of Grotta di Castelcivita modified after Gambassini 46 .Layers highlighted in red are the ones analyzed in this paper.(b, c, d) Planimetry of the excavation surfaces in ars, gic, and rsa'.The areas colored in red were excavated by P. Gambassini and sampled in this study.For more information about layer gic, please refer to Supplementary Fig. S1.Relief and graphics: P. Gambassini, M.P. Fumanal, A. Moroni, and V. Spagnolo.

Figure 4 .
Figure 4. Various perspectives of the 3D models and schematic drawings of cores associated with blade and bladelet production found in layers rsa' and gic.The numbers shown after the letters are from the dataset created by AF.In both the dataset and the 3D model repository, they are prefixed with "CTC", which is the common acronym for the site.Cores are classified as semi-circumferential (a, e, h, and k), carinated (b, c, d, g, i, j, l, n, and o), wide-faced flat (m), and narrow-sided (f).The scale refers to the schematic drawing, while the 3D views are half-sized.Drawings by A. Falcucci.

Figure 5 .
Figure 5. Scatterplots showing the length and width measurements (in mm) of the last successful blade or bladelet removals on laminar cores (triangles) and the dimensions of all complete blades and bladelets (circles) across the studied assemblages.Refer to the legend for corresponding colors.

Figure 6 .
Figure 6.Visualization of the results of the first and second components of the PCA conducted on laminar cores.(a) Shows the scree plot and the high percentage of explained variance of the first component.(b) Shows a biplot with the contribution of the different quantitative variables to the first and second components.(cand d) Display the distribution of the studied cores in the PC1 to PC2 space, sorted according to layer (c) and core classification (d).In (b), FSL stands for flaking surface length, FSL/T is the ratio between flaking surface length and core thickness, FSL/W is the ratio between flaking surface length and core width.The category Narrow/ Burin includes narrow-sided cores and burin cores, which were merged due to their low number and the similarity in the core geometric configuration.Initial cores and core shatters were excluded from the analysis.

Figure 7 .
Figure 7. Selection of retouched bladelets from rsa' and gic.Additional photos of retouched bladelets from gic and ars can be found in Supplementary Figs.S14-S15.The number following the alphabetical list corresponds to the ID assigned by AF during the techno-typological analysis (refer to the provided dataset for details).Tools are sorted by the position of the retouch: direct bilateral retouch (a, c-f, h-p, s, and v), direct unilateral (b, g, and u), inverse (q), and alternate (r and t).Photos by A. Falcucci.

Figure 8 .
Figure 8.(a) Displays the percentage of bladelets modified by alternate, inverse, and direct retouching.(b) Shows boxplots with jittered points of length values (in millimeters) for all complete retouched bladelets, along with the results of the Wilcoxon test, confirming significant differences between the two assemblages.Width and thickness values, along with metric data tables, are available in the Supplementary Information.

Figure 9 .
Figure 9. Results of the 2D shape analysis of the complete bladelet dataset.(a) Displays the shape variation across the first four PCs (SD stands for standard deviation).(b) Shows the boxplots comparing the PC1 scores of the analyzed datasets from gic and rsa', sorted according to the presence and type of retouch.(c) Is the scatterplot of PC axes 1 and 2 with the mean values of each group displayed as a larger dot.Alternate and inverse retouching are merged into a single category labeled as "alt.-inv.".

Table 5 .
General overview of the main tool categories recovered across the studied sequence with percentages provided in brackets.Undet Undetermined.