New evidence of early Neanderthal disappearance in the Iberian Peninsula

The time between Palaeolithic hearths

Resolving the timescale of human activity in the Palaeolithic Age is one of the most challenging problems in prehistoric archaeology. The duration and frequency of hunter-gatherer camps reflect key aspects of social life and human-environment interactions. However, the time dimension of Palaeolithic contexts is generally inaccurately reconstructed because of the limitations of dating techniques1, the impact of disturbing agents on sedimentary deposits2 and the palimpsest effect3,4. Here we report high-resolution time differences between six Middle Palaeolithic hearths from El Salt Unit X (Spain) obtained through archaeomagnetic and archaeostratigraphic analyses. The set of hearths covers at least around 200-240 years with 99% probability, having decade- and century-long intervals between the different hearths. Our results provide a quantitative estimate of the time framework for the human occupation events included in the studied sequence. This is a step forward in Palaeolithic archaeology, a discipline in which human behaviour is usually approached from a temporal scale typical of geological processes, whereas significant change may happen at the smaller scales of human generations. Here we reach a timescale close to a human lifespan.

Compound-specific carbon isotope analysis of short-chain fatty acids from Pine tissues: characterizing paleo-fire residues and plant exudates

Different types of plant tissues and resin can account for the wax lipids found in sedimentary contexts and archaeological samples. Consequently, there is increasing research to characterize the fatty acid carbon isotope ratios of different plant anatomical parts and their plant exudates (resin). With the aim to explore isotopic differences between plant tissues, state of the fine organic matter, effect of thermal degradation, and to identify plant residues we measured the δ13C values of short-chain fatty acids (δ13C16:0 and δ13C18:0) in: i) dead and fresh (collected and immediately dried) pine needles and branches (Pinus canariensis) and pine resin from laboratory-controlled heating experiments and ii) sediment and charred pine tissue samples from a wild pine forest fire. Our results are compared to previously published experimental open-air fire experiments and pine-fuelled archaeological combustion features. We found that for both fatty acid types, there are differences in δ13C signatures among anatomical parts and initial moisture content. These data allow us to characterize the isotopic signature of pine tissue and the effect of degradation on isotopic biomarkers, as well as to estimate combustion temperatures in pine-fuelled anthropogenic fires.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12520-023-01815-3.

Assessing climatic impact on transition from Neanderthal to anatomically modern human population on Iberian Peninsula: a macroscopic perspective

The Iberian Peninsula is of particular interest for the research on the Neanderthal (NEA) to anatomically modern human (AMH) population transition. The AMHs arrived in Iberia last from Eastern Europe and thus any possible contacts between the two populations occurred here later than elsewhere. The transition process took place in the earlier part of the Marine Isotope Stage 3 (∼60-27 cal ka BP) as repeated and profound climate changes challenged the population stability. To investigate how climate change and population interactions influenced the transition, we combine climate data with archaeological-site data to reconstruct the Human Existence Potential, a measure of the probability of human existence, for both the NEA and AMH populations in the Greenland Interstadial 11-10 (GI11-10) and Stadial 10-9/Heinrich event 4 (GS10-9/HE4) times. It is found that during GS10-9/HE4, large parts of the peninsula became unsuitable for NEA human existence and the NEA settlement areas contracted to isolated coastal hot spots. As a consequence, the NEA networks became highly unstable, triggering the final collapse of the population. The AMHs arrived in Iberia in GI10 but were confined to patches in the northern most strip of the peninsula. They were soon facing the much colder climate of GS10-9/HE4, which prevented their further expansion or even caused a contraction of their settlement areas. Thus, due to the constellation of climate change and the dispersal of the two populations into different regions of the peninsula, it is unlikely that the NEAs and AMHs coexisted in extensive areas and the AMHs had a significant influence on the demography of the NEAs.

A Neandertal dietary conundrum: Insights provided by tooth enamel Zn isotopes from Gabasa, Spain

The characterization of Neandertals' diets has mostly relied on nitrogen isotope analyses of bone and tooth collagen. However, few nitrogen isotope data have been recovered from bones or teeth from Iberia due to poor collagen preservation at Paleolithic sites in the region. Zinc isotopes have been shown to be a reliable method for reconstructing trophic levels in the absence of organic matter preservation. Here, we present the results of zinc (Zn), strontium (Sr), carbon (C), and oxygen (O) isotope and trace element ratio analysis measured in dental enamel on a Pleistocene food web in Gabasa, Spain, to characterize the diet and ecology of a Middle Paleolithic Neandertal individual. Based on the extremely low δ⁶⁶Zn value observed in the Neandertal's tooth enamel, our results support the interpretation of Neandertals as carnivores as already suggested by δ¹⁵N isotope values of specimens from other regions. Further work could help identify if such isotopic peculiarities (lowest δ⁶⁶Zn and highest δ¹⁵N of the food web) are due to a metabolic and/or dietary specificity of the Neandertals.

Three-Dimensional Comparative Study of Human Bipartite Scaphoids and the Os Centrale of the Wrist in Neandertals and Non-Human Anthropoid Primates

In humans, bipartite scaphoid still does not differentiate clearly from traumatic non-union of the scaphoid. To aid diagnosis, we sought to analyze the main geometrical similarities among bipartite scaphoids from primate species with fused and unfused scaphoid centrales. Four human embryos, four cases of adult humans with bipartite scaphoid, twelve adult specimens of other extant anthropoid primates, and two Neandertal scaphoid specimens were included in this study. Three-dimensional polygon models of the scaphoid and os centrale were generated from CT scan, micro-CT scan, or histological sections. A 3D comparative study of the morphological and morphometrical parameters was performed using the MSC Patran software. The os centrale was smaller than the scaphoid in all specimens and its shape was elongated in the anteroposterior scaphoid direction. The position of the os centrale centroid compared to the scaphoid using direction vectors had a strong orientation along the proximodistal axis in all species. The main morphological feature of bipartite scaphoid was the continuity of the scaphoid from its proximal pole to its tubercule along the anteroposterior axis. In all specimens, if the os centrale was removed, the scaphoid still appeared normal and whole. The bipartite scaphoid in adult humans shares geometrical analogies with monkeys and orangutans, human embryos, and Neandertals. Morphological and morphometrical features identified in this study are useful to differentiate bipartite scaphoid from scaphoid pseudarthrosis. All other criteria suggested in the past lead to misdiagnosis.

Revisiting the Middle and Upper Palaeolithic archaeology of Gruta do Caldeirão (Tomar, Portugal)

Gruta do Caldeirão features a c. 6 m-thick archaeological stratification capped by Holocene layers ABC-D and Ea, which overlie layer Eb, a deposit of Magdalenian age that underwent significant disturbance, intrusion, and component mixing caused by funerary use of the cave during the Early Neolithic. Here, we provide an updated overview of the stratigraphy and archaeological content of the underlying Pleistocene succession, whose chronology we refine using radiocarbon and single-grain optically stimulated luminescence dating. We find a high degree of stratigraphic integrity. Dating anomalies exist in association with the succession’s two major discontinuities: between layer Eb and Upper Solutrean layer Fa, and between Early Upper Palaeolithic layer K and Middle Palaeolithic layer L. Mostly, the anomalies consist of older-than-expected radiocarbon ages and can be explained by bioturbation and palimpsest-forming sedimentation hiatuses. Combined with palaeoenvironmental inferences derived from magnetic susceptibility analyses, the dating shows that sedimentation rates varied in tandem with the oscillations in global climate revealed by the Greenland oxygen isotope record. A steep increase in sedimentation rate is observed through the Last Glacial Maximum, resulting in a c. 1.5 m-thick accumulation containing conspicuous remains of occupation by people of the Solutrean technocomplex, whose traditional subdivision is corroborated: the index fossils appear in the expected stratigraphic order; the diagnostics of the Protosolutrean and the Lower Solutrean predate 24,000 years ago; and the constraints on the Upper Solutrean place it after Greenland Interstadial 2.2. (23,220–23,340 years ago). Human usage of the site during the Early Upper and the Middle Palaeolithic is episodic and low-intensity: stone tools are few, and the faunal remains relate to carnivore activity. The Middle Palaeolithic is found to persist beyond 39,000 years ago, at least three millennia longer than in the Franco-Cantabrian region. This conclusion is upheld by Bayesian modelling and stands even if the radiocarbon ages for the Middle Palaeolithic levels are removed from consideration (on account of observed inversions and the method’s potential for underestimation when used close to its limit of applicability). A number of localities in Spain and Portugal reveal a similar persistence pattern. The key evidence comes from high-resolution fluviatile contexts spared by the site formation issues that our study of Caldeirão brings to light—palimpsest formation, post-depositional disturbance, and erosion. These processes. are ubiquitous in the cave and rock-shelter sites of Iberia, reflecting the impact on karst archives of the variation in climate and environments that occurred through the Upper Pleistocene, and especially at two key points in time: between 37,000 and 42,000 years ago, and after the Last Glacial Maximum. Such empirical difficulties go a long way towards explaining the controversies surrounding the associated cultural transitions: from the Middle to the Upper Palaeolithic, and from the Solutrean to the Magdalenian. Alongside potential dating error caused by incomplete decontamination, proper consideration of sample association issues is required if we are ever to fully understand what happened with the human settlement of Iberia during these critical intervals, and especially so with regards to the fate of Iberia’s last Neandertal populations.

Evaluating Causes of Current Genetic Gradients of Modern Humans of the Iberian Peninsula

The history of modern humans in the Iberian Peninsula includes a variety of population arrivals sometimes presenting admixture with resident populations. Genetic data from current Iberian populations revealed an overall east–west genetic gradient that some authors interpreted as a direct consequence of the Reconquista, where Catholic Kingdoms expanded their territories toward the south while displacing Muslims. However, this interpretation has not been formally evaluated. Here, we present a qualitative analysis of the causes of the current genetic gradient observed in the Iberian Peninsula using extensive spatially explicit computer simulations based on a variety of evolutionary scenarios. Our results indicate that the Neolithic range expansion clearly produces the orientation of the observed genetic gradient. Concerning the Reconquista (including political borders among Catholic Kingdoms and regions with different languages), if modeled upon a previous Neolithic expansion, it effectively favored the orientation of the observed genetic gradient and shows local isolation of certain regions (i.e., Basques and Galicia). Despite additional evolutionary scenarios could be evaluated to more accurately decipher the causes of the Iberian genetic gradient, here we show that this gradient has a more complex explanation than that previously hypothesized.

Components of a Neanderthal gut microbiome recovered from fecal sediments from El Salt

A comprehensive view of our evolutionary history cannot ignore the ancestral features of our gut microbiota. To provide some glimpse into the past, we searched for human gut microbiome components in ancient DNA from 14 archeological sediments spanning four stratigraphic units of El Salt Middle Paleolithic site (Spain), including layers of unit X, which has yielded well-preserved Neanderthal occupation deposits dating around 50 kya. According to our findings, bacterial genera belonging to families known to be part of the modern human gut microbiome are abundantly represented only across unit X samples, showing that well-known beneficial gut commensals, such as Blautia, Dorea, Roseburia, Ruminococcus, Faecalibacterium and Bifidobacterium already populated the intestinal microbiome of Homo since as far back as the last common ancestor between humans and Neanderthals.

A revised AMS and tephra chronology for the Late Middle to Early Upper Paleolithic occupations of Ortvale Klde, Republic of Georgia

The nature and timing of the shift from the Late Middle Paleolithic (LMP) to the Early Upper Paleolithic (EUP) varied geographically, temporally, and substantively across the Near East and Eurasia; however, the result of this process was the archaeological disappearance of Middle Paleolithic technologies across the length and breadth of their geographic distribution. Ortvale Klde rockshelter (Republic of Georgia) contains the most detailed LMP-EUP archaeological sequence in the Caucasus, an environmentally and topographically diverse region situated between southwest Asia and Europe. Tephrochronological investigations at the site reveal volcanic ash (tephra) from various volcanic sources and provide a tephrostratigraphy for the site that will facilitate future correlations in the region. We correlate one of the cryptotephra layers to the large, caldera-forming Nemrut Formation eruption (30,000 years ago) from Nemrut volcano in Turkey. We integrate this tephrochronological constraint with new radiocarbon dates and published ages in an OxCal Bayesian age model to produce a revised chronology for the site. This model increases the ages for the end of the LMP (∼47.5-44.2 ka cal BP) and appearance of the EUP (∼46.7-43.6 ka cal BP) at Ortvale Klde, which are earlier than those currently reported for other sites in the Caucasus but similar to estimates for specific sites in southwest Asia and eastern Europe. These data, coupled with archaeological, stratigraphic, and taphonomic observations, suggest that at Ortvale Klde, (1) the appearance of EUP technologies of bone and stone has no technological roots in the preceding LMP, (2) a LMP population vacuum likely preceded the appearance of these EUP technologies, and (3) the systematic combination of tephra correlations and absolute dating chronologies promises to substantially improve our inter-regional understanding of this critical time interval of human evolution and the potential interconnectedness of hominins at different sites.

Micro-contextual identification of archaeological lipid biomarkers using resin-impregnated sediment slabs

Characterizing organic matter preserved in archaeological sediment is crucial to behavioral and paleoenvironmental investigations. This task becomes particularly challenging when considering microstratigraphic complexity. Most of the current analytical methods rely on loose sediment samples lacking spatial and temporal resolution at a microstratigraphic scale, adding uncertainty to the results. Here, we explore the potential of targeted molecular and isotopic biomarker analysis on polyester resin-impregnated sediment slabs from archaeological micromorphology, a technique that provides microstratigraphic control. We performed gas chromatography-mass spectrometry (GC-MS) and gas chromatography-isotope ratio mass spectromety (GC-IRMS) analyses on a set of samples including drill dust from resin-impregnated experimental and archaeological samples, loose samples from the same locations and resin control samples to assess the degree of interference of polyester resin in the GC-MS and Carbon-IRMS signals of different lipid fractions (n-alkanes, aromatics, n-ketones, alcohols, fatty acids and other high polarity lipids). The results show that biomarkers within the n-alkane, aromatic, n-ketone, and alcohol fractions can be identified. Further work is needed to expand the range of identifiable lipid biomarkers. This study represents the first micro-contextual approach to archaeological lipid biomarkers and contributes to the advance of archaeological science by adding a new method to obtain behavioral or paleoenvironmental proxies.

The early Aurignacian dispersal of modern humans into westernmost Eurasia

We report the remarkable discovery of an early Aurignacian occupation, ∼5,000 years older than any Upper Paleolithic site in westernmost Eurasia. The archaeological and radiocarbon data provide definitive evidence that modern humans were in western Iberia at a time when, if present at all, Neanderthal populations would have been extremely sparse. This discovery has important ramifications for our understanding of the process of modern human dispersal and replacement of Neanderthal populations. The results support a very rapid, unimpeded dispersal of modern humans across western Eurasia and support the notion that climate and environmental change played a significant role in this process.

Documenting the first appearance of modern humans in a given region is key to understanding the dispersal process and the replacement or assimilation of indigenous human populations such as the Neanderthals. The Iberian Peninsula was the last refuge of Neanderthal populations as modern humans advanced across Eurasia. Here we present evidence of an early Aurignacian occupation at Lapa do Picareiro in central Portugal. Diagnostic artifacts were found in a sealed stratigraphic layer dated 41.1 to 38.1 ka cal BP, documenting a modern human presence on the western margin of Iberia ∼5,000 years earlier than previously known. The data indicate a rapid modern human dispersal across southern Europe, reaching the westernmost edge where Neanderthals were thought to persist. The results support the notion of a mosaic process of modern human dispersal and replacement of indigenous Neanderthal populations.

Fire and brief human occupations in Iberia during MIS 4: Evidence from Abric del Pastor (Alcoy, Spain)

There is a relatively low amount of Middle Paleolithic sites in Europe dating to MIS 4. Of the few that exist, several of them lack evidence for anthropogenic fire, raising the question of how this period of global cooling may have affected the Neanderthal population. The Iberian Peninsula is a key area to explore this issue, as it has been considered as a glacial refugium during critical periods of the Neanderthal timeline and might therefore yield archaeological contexts in which we can explore possible changes in the behaviour and settlement patterns of Neanderthal groups during MIS 4. Here we report recent data from Abric del Pastor, a small rock shelter in Alcoy (Alicante, Spain) with a stratified deposit containing Middle Palaeolithic remains. We present absolute dates that frame the sequence within MIS 4 and multi-proxy geoarchaeological evidence of in situ anthropogenic fire, including microscopic evidence of in situ combustion residues and thermally altered sediment. We also present archaeostratigraphic evidence of recurrent, functionally diverse, brief human occupation of the rock shelter. Our results suggest that Neanderthals occupied the Central Mediterranean coast of the Iberian Peninsula during MIS 4, that these Neanderthals were not undergoing climatic stress and they were habitual fire users.

Late Glacial rapid climate change and human response in the Westernmost Mediterranean (Iberia and Morocco)

This paper investigates the correlation between climate, environment and human land use in the Westernmost Mediterranean on both sides of the Strait of Gibraltar during the Late Glacial. Using a multi-proxy approach on a sample of 300 sites from the Solutrean and Magdalenian of the Iberian Peninsula and from the Iberomaurusian in Morocco, we find evidence for significant changes in settlement patterns and site density after the Last Glacial Maximum. In Southern Iberia, during Heinrich Stadial 1, hyperarid zones expanded drastically from the south-eastern coast to the West through the Interior. This aridification process heavily affected Magdalenian settlement in the South and caused a strong decline of hunter-gatherer population. Southern Iberia during Heinrich Stadial 1 turned out to be a high-risk environment when compared to Northern Iberia. At the same time, the Late Iberomaurusian of Morocco, although considered to be situated in a high-risk environment as well, experiences an increase of sites and expansion of settlement area.

Living on the edge: Was demographic weakness the cause of Neanderthal demise?

The causes of disappearance of the Neanderthals, the only human population living in Europe before the arrival of Homo sapiens, have been debated for decades by the scientific community. Different hypotheses have been advanced to explain this demise, such as cognitive, adaptive and cultural inferiority of Neanderthals. Here, we investigate the disappearance of Neanderthals by examining the extent of demographic changes needed over a period of 10,000 years (yrs) to lead to their extinction. In regard to such fossil populations, we inferred demographic parameters from present day and past hunter-gatherer populations, and from bio-anthropological rules. We used demographic modeling and simulations to identify the set of plausible demographic parameters of the Neanderthal population compatible with the observed dynamics, and to explore the circumstances under which they might have led to the disappearance of Neanderthals. A slight (<4%) but continuous decrease in the fertility rate of younger Neanderthal women could have had a significant impact on these dynamics, and could have precipitated their demise. Our results open the way to non-catastrophic events as plausible explanations for Neanderthal extinction.

Insights into the timing, intensity and natural setting of Neanderthal occupation from the geoarchaeological study of combustion structures: A micromorphological and biomarker investigation of El Salt, unit Xb, Alcoy, Spain

Middle Paleolithic lithic and faunal assemblages throughout Eurasia reflect short-term Neanderthal occupations, which suggest high group mobility. However, the timing of these short-term occupations, a key factor to assess group mobility and territorial range, remains unresolved. Anthropogenic combustion structures are prominent in the Middle Paleolithic record and conceal information on the timing and intensity and natural setting of their associated human occupations. This paper examines a concentration of eleven combustion structures from unit Xb of El Salt, a Middle Paleolithic site in Spain through a geoarchaeological approach, in search of temporal, human impact and paleoenvironmental indicators to assess the timing, intensity and natural setting of the associated human occupations. The study was conducted using micromorphology, lipid biomarker analysis and compound specific isotope analysis. Results show in situ hearths built on different diachronic topsoils rich in herbivore excrements and angiosperm plant residues with rare anthropogenic remains. These data are suggestive of low impact, short-term human occupations separated by relatively long periods of time, with possible indicators of seasonality. Results also show an absence of conifer biomarkers in the mentioned topsoils and presence of conifer charcoal among the fuel residues (ash), indicating that fire wood was brought to the site from elsewhere. A microscopic and molecular approach in the study of combustion structures allows us to narrow down the timescale of archaeological analysis and contributes valuable information towards an understanding of Neanderthal group mobility and settlement patterns.

The Lowermost Tejo River Terrace at Foz do Enxarrique, Portugal: A Palaeoenvironmental Archive from c. 60–35 ka and Its Implications for the Last Neanderthals in Westernmost Iberia

Reconstruction of Pleistocene environments and processes in the sensitive geographical location of westernmost Iberia, facing the North Atlantic Ocean, is crucial for understanding impacts on early human communities. We provide a characterization of the lowest terrace (T6) of the Lower Tejo River, at Vila Velha de Ródão (eastern central Portugal). This terrace comprises a lower gravel bed and an upper division consisting of fine to very fine sands and coarse silts. We have used a multidisciplinary approach, combining geomorphology, optically stimulated luminescence (OSL) dating, grain-size analysis and rock magnetism measurement, in order to provide new insights into the environmental changes coincident with the activity of the last Neanderthals in this region. In addition, we conducted palynological analysis, X-ray diffraction measurement and scanning electron microscopy coupled with energy dispersive spectra of the clay fraction and carbonate concretions. We discuss these new findings in the context of previously published palaeontological and archeological data. The widespread occurrence of carbonate concretions and rizoliths in the T6 profile is evidence for episodic pedogenic evaporation, in agreement with the rare occurrence and poor preservation of phytoliths. We provide updated OSL ages for the lower two Tejo terraces, obtained by post infra-red stimulated luminescence: (i) T5 is c. 140 to 70 ka; (ii) T6 is c. 60 to 35 ka. The single archaeological and fossiliferous level located at the base of the T6 upper division, recording the last regional occurrence of megafauna (elephant and rhinoceros) and Mousterian artefacts, is now dated at 44 ± 3 ka. With reference to the arrival of Neanderthals in the region, probably by way of the Tejo valley (from central Iberia), new dating suggests a probable age of 200–170 ka for the earliest Mousterian industry located in the topmost deposits of T4.

Climate deteriorations and Neanderthal demise in interior Iberia

Time and circumstances for the disappearance of Neanderthals and its relationship with the advent of Modern Humans are not yet sufficiently resolved, especially in case of the Iberian Peninsula. Reconstructing palaeoenvironmental conditions during the last glacial period is crucial to clarifying whether climate deteriorations or competition and contacts with Modern Humans played the pivotal role in driving Neanderthals to extinction. A high-resolution loess record from the Upper Tagus Basin in central Spain demonstrates that the Neanderthal abandonment of inner Iberian territories 42 kyr ago coincided with the evolvement of hostile environmental conditions, while archaeological evidence testifies that this desertion took place regardless of modern humans’ activities. According to stratigraphic findings and stable isotope analyses, this period corresponded to the driest environmental conditions of the last glacial apart from an even drier period linked to Heinrich Stadial 3. Our results show that during Marine Isotope Stages (MIS) 4 and 2 climate deteriorations in interior Iberia temporally coincided with northern hemisphere cold periods (Heinrich stadials). Solely during the middle MIS 3, in a period surrounding 42 kyr ago, this relation seems not straightforward, which may demonstrate the complexity of terrestrial climate conditions during glacial periods.

Precise dating of the Middle-to-Upper Paleolithic transition in Murcia (Spain) supports late Neandertal persistence in Iberia

The late persistence in Southern Iberia of a Neandertal-associated Middle Paleolithic is supported by the archeological stratigraphy and the radiocarbon and luminescence dating of three newly excavated localities in the Mula basin of Murcia (Spain). At Cueva Antón, Mousterian layer I-k can be no more than 37,100 years-old. At La Boja, the basal Aurignacian can be no less than 36,500 years-old. The regional Middle-to-Upper Paleolithic transition process is thereby bounded to the first half of the 37th millennium Before Present, in agreement with evidence from Andalusia, Gibraltar and Portugal. This chronology represents a lag of minimally 3000 years with the rest of Europe, where that transition and the associated process of Neandertal/modern human admixture took place between 40,000 and 42,000 years ago. The lag implies the presence of an effective barrier to migration and diffusion across the Ebro river depression, which, based on available paleoenvironmental indicators, would at that time have represented a major biogeographical divide. In addition, (a) the Phlegraean Fields caldera explosion, which occurred 39,850 years ago, would have stalled the Neandertal/modern human admixture front because of the population sink it generated in Central and Eastern Europe, and (b) the long period of ameliorated climate that came soon after (Greenland Interstadial 8, during which forests underwent a marked expansion in Iberian regions south of 40°N) would have enhanced the “Ebro Frontier” effect. These findings have two broader paleoanthropological implications: firstly, that, below the Ebro, the archeological record made prior to 37,000 years ago must be attributed, in all its aspects and components, to the Neandertals (or their ancestors); secondly, that modern human emergence is best seen as an uneven, punctuated process during which long-lasting barriers to gene flow and cultural diffusion could have existed across rather short distances, with attendant consequences for ancient genetics and models of human population history.

A context for the last Neandertals of interior Iberia: Los Casares cave revisited

Introduction and objectives

Although the Iberian Peninsula is a key area for understanding the Middle to Upper Paleolithic transition and the demise of the Neandertals, valuable evidence for these debates remains scarce and problematic in its interior regions. Sparse data supporting a late Neandertal persistence in the Iberian interior have been recently refuted and hence new evidence is needed to build new models on the timing and causes of Neandertal disappearance in inland Iberia and the whole peninsula. In this study we provide new evidence from Los Casares, a cave located in the highlands of the Spanish Meseta, where a Neandertal-associated Middle Paleolithic site was discovered and first excavated in the 1960’s. Our main objective is twofold: (1) provide an updated geoarcheological, paleoenvironmental and chronological framework for this site, and (2) discuss obtained results in the context of the time and nature of the last Neandertal presence in Iberia.

Methods

We conducted new fieldwork in an interior chamber of Los Casares cave named ‘Seno A’. Our methods included micromorphology, sedimentology, radiocarbon dating, Uranium/Thorium dating, palinology, microfaunal analysis, anthracology, phytolith analysis, archeozoology and lithic technology. Here we present results on site formation processes, paleoenvironment and the chronological setting of the Neandertal occupation at Los Casares cave-Seno A.

Results and discussion

The sediment sequence reveals a mostly in situ archeological deposit containing evidence of both Neandertal activity and carnivore action in level c, dated to 44,899–42,175 calendar years ago. This occupation occurred during a warm and humid interval of Marine Isotopic Stage 3, probably correlating with Greenland Interstadial 11, representing one of the latest occurrences of Neandertals in the Iberian interior. However, overlying layer b records a deterioration of local environments, thus providing a plausible explanation for the abandonment of the site, and perhaps for the total disappearance of Neandertals of the highlands of inland Iberia during subsequent Greenland Stadials 11 or 10, or even Heinrich Stadial 4. Since layer b provided very few signs of human activity and no reliable chronometric results, and given the scarce chronostratigrapic evidence recorded so far for this period in interior Iberia, this can only be taken as a working hypothesis to be tested with future research. Meanwhile, 42,000 calendar years ago remains the most plausible date for the abandonment of interior Iberia by Neandertals, possibly due to climate deterioration. Currently, a later survival of this human species in Iberia is limited to the southern coasts.

Reading the landscape: Legible environments and hominin dispersals

Wayfinding, or the ability to plan and navigate a course over the landscape, is a subject of investigation in geography, neurophysiology, psychology, urban planning, and landscape design. With the prevalence of GPS-assisted navigation systems, or "wayfinders," computer scientists are also increasingly interested in understanding how people plan their movements and guide others. However, the importance of wayfinding as a process that regulates human mobility has only recently been incorporated into archeological research design. Hominin groups were able to disperse widely during the course of prehistory. The scope of these dispersals speaks to the innate navigation abilities of hominins. Their long-term success must have depended on an ability to communicate spatial information effectively. Here, we consider the extent to which some landscapes may have been more conducive to wayfinding than others. We also describe a tool we have created for quantifying landscape legibility (sensu Gollege), a complex and under-explored concept in archeology, with a view to investigating the impact of landscape structure on human wayfinding and thus, patterns of dispersal during prehistory. To this end, we have developed a method for quantifying legibility using a Geographic Information System (GIS) and apply it to a test case in prehistoric Iberia.

On the local Mousterian origin of the Châtelperronian: Integrating typo-technological, chronostratigraphic and contextual data

Across Europe the period 45-40 ka (thousands of years ago) is associated with several technological changes, including the emergence of the Châtelperronian technocomplex in France and northern Spain. The Châtelperronian, stratigraphically located between the Mousterian and Aurignacian, is characterized by Upper Palaeolithic features, such as volumetric blade reduction, curved backed blades, end-scrapers, bladelets, bone tools and ornaments. Concurrently, repeated, though debated, associations with Neanderthal remains and Mousterian elements suggest a local technological development. Following recent critiques and cumulating technological studies, this paper provides data-driven contextualisations of the Châtelperronian and late Mousterian archaeological records and a primary comparative assessment of a major linking element, backed knives, to re-assess the origin of the Châtelperronian. The results demonstrate the challenging nature of the 50-35 ka record, with many interpretive problems caused by poorly recorded excavations, resulting in only 25 well-contextualised assemblages from the claimed 143 Châtelperronian find spots. These 25 assemblages facilitate more detailed chronostratigraphic and typo-technological assessments and show that the Châtelperronian has a homogenous set of technologies and tools. A similar evaluation of the late Mousterian indicates a wide-ranging late Neanderthal skill set, commonly including laminar blank production and backing. Further, conceptual similarities were noted both in blank selection and edge modification between Mousterian and Châtelperronian backed knives, alongside their near-absence in other, contemporaneous technocomplexes. A Europe-wide contextualisation shows that while the current coarse-grained record still allows for several potential scenarios, the data throughout this paper point towards a most parsimonious model of a Châtelperronian made by Neanderthals, with roots in the late Middle Palaeolithic technological skill set. However, this change seems triggered by early arrivals of modern humans either indirectly, through stimulus diffusion, or directly, after ca. 42 ka. Fully testing this model requires an ongoing focus on site formation and assemblage integrity, alongside in-depth analyses of recently excavated assemblages and existing collections.