Socioeconomic, Technological, and Cultural Adaptation of the Mesolithic Population in Central - Eastern Cantabria ( Spain ) in the Early and Middle Holocene

: This article presents the research on the palaeoenvironmental changes that took place at the end of the Tardiglacial, in the early and middle Holocene, observed in sites of anthropic origin in central - eastern Cantabria. Through the comparative analysis of the economy, the settlement pattern, and the industries of the Azilian and Mesolithic settlements, we try to infer the repercussions they could have had on the last hunter - gatherers, in order to adapt to the modi ﬁ cation of the territory, the change in the available resources, and the socio - economic consequences they could have had on the settlement. The radiocarbon record of central - eastern Cantabria and the Cantabrian region ( Northern Spain ) between 9.5 and 7.9 ka cal BP is analysed in order to assess the impact of the cold events that occurred in 9.3 and 8.2 ka cal BP, identi ﬁ ed in the palaeoenvironment.


Introduction
The climate and environmental changes at the start of the Holocene affected the way of life of the last hunter-gatherers.In the Cantabrian region (N.Spain), these changes transformed the geomorphological characteristics of the territory and the modification of the Palaeoenvironment, generating changes in subsistence strategies, technology, and settlement pattern.
After the Younger Dryas, about 11.6 ka BP, at the start of the Holocene, the population in central-eastern Cantabria corresponded culturally with the late Azilian and the initial and middle Mesolithic.The Azilian started in the temperate Allerød period, in about 14.5 ka BP in the Cantabrian region (Álvarez-Alonso, 2008, p. 75), and continued until 10.9 ka cal BP in El Mirón (Straus & González Morales, 2003) where the Mesolithic cultural change is identified.
The Azilian was first systematised in Cantabrian region (N.Spain) by Fernández-Tresguerres Velasco (1980, 1995, 2004, 2006), who compiled the information available about a series of sites in Asturias and Cantabria (then known as Santander), characterised it, and established its cultural sequence.García Guinea 3 Materials and Methods

Palaeoenvironmental Evolution in the Early and Middle Holocene
The transition from the Late Ice Age to the Holocene was marked by a series of climate oscillations owing to the advances and withdrawals of the Arctic ice sheet and mountain glaciers, generated by deglaciation and the response of the thermohaline circulation (THC) (Broecker & Denton, 1989;Marshall et al., 2007;Wunsch, 2002).Cantabrian Spain was affected by the North Atlantic Oscillation and by the advection of oceanic hear in the North Atlantic due to variability in the Atlantic Meridional Overturning Circulation (Mary et al., 2017).
After the Younger Dryas in about 11.6 cal BP, as the ocean currents adopted their present functioning, the Holocene commenced.In the Greenlandian phase (11.7 to 8.2 ka BP), the most notable characteristic is the decreasing trend of the GAR-01 data from 3.84‰ at 11.7 ka BP to 4.99‰ at 8.2 ka BP.The greatest drop in this time was in a very short period in about 9.0 ka BP.This may reflect the effect of a pulse of cold water when the Baltic dyke collapsed, which weakened the THC and lowered temperatures by an average of 4°C in 100 years (Fleitmann et al., 2008;Marshall et al., 2007).The last abrupt change in the THC occurred between 8400 and 8000 cal BP, the 8.2 ka event, due to the entry of meltwater from the Laurentide ice sheet, which has been detected in Greenland and Europe (Barber et al., 1999;Clarke, Leverington, Teller, & Dyke, 2003;Wiersma & Renssen, 2006).the Suances estuary to the west and the Ontón estuary to the east, located on the coastline, coastal plain, and associated with inland and high valleys.Magny, Bégeot, Guiot, and Peyron (2003) suppose that the cold pulse would coincide with dry conditions in the south and north of Europe, and a humid climate in middle European latitudes (north of Italy and the Iberian Peninsula, France, Central Europe, Netherlands, etc.) with the boundary between one situation and the other at about 38 or 40°N (in the centre of the Iberian Peninsula).For López Sáez, López-Merino, and Pérez Díaz (2008), it is more likely that the boundary would be at about 41-42°N, which would apply to the north of Iberia (north of Galicia, Cantabrian region (N Spain), Pyrenees), where the 8.2 ka BP event would give rise to humid conditions.
In Cantabria, in the area of study, both the 9.3 ka and the 8.2 ka events have been identified in research on anomalies in the growth of a stalagmite in Cueva de La Garma (Baldini et al., 2019), to determine the potential role of changes in the seasonality of rain and temperature in the ẟ 18 O record.In the Greenlandian period, the expression of the 9.2 ka event in GAR-01 is similar in magnitude to the YD ẟ 18 O anomaly (Baldini et al., 2019) with ẟ 18 O values between 5.08 and 5.00‰, respectively.The anomaly observed in the stalagmite suggests that the summer precipitation was very scanty, and this is related to the displacement north of the Azores anticyclone, leading to extremely arid summers by sustained rain in winter (Baldini et al., 2019).The 8.2 ka event is evident in the GAR-01 ẟ 18 O record at 8.16 ka BP as an anomaly of 0.7‰ (in relation to the mean of 4.37‰ in the Holocene), but it is relatively mild compared with the negative ẟ 18 O anomaly in GAR-01 at −9 ka BP.Winter temperatures reached a local minimum of 10°C (compared with 11.7°C in the early Holocene).This is the lowest modelled temperature for the Holocene, and winter precipitation was heavier than at present (Baldini et al., 2019).
Associated with these cold events, anthropic and chronological hiatuses have been observed at some sites in the area of study, while in other cases, erosion caused by run-off and water circulation has been seen at El Carabión (Pérez-Bartolomé, 2014b;Pérez-Bartolomé et al., 2016) and Cueva de Sopeña (Pérez-Bartolomé, 2016c and 2019), or the absence of archaeological evidence and dates (Carabión, ibidem), (Las Salinas, Pérez-Bartolomé, 2019 and 2021), among others listed in Section 8.This process has also been documented in the natural record in the Los Tornos peat bog (Soba, Cantabria) (Muñoz Sobrino, Ramil Rego, Gómez-Orellana, & Díaz Varela, 2005), where a sedimentary hiatus was identified, with the loss of about 3,000 years in the 3 cm-thick peat that separated the date at the base of 8596 cal BP from 5317 cal BP for Zone 6.This indicates irregularity in the deposit and/or above all its erosion.

Changes in the Territory: Variations in Sea Level and Its Impact on the Formation of New Landscapes
Climate change in the Holocene was the cause of variations in sea level and the position of the shore, which led to a reduction in the available territory along the coast and the formation of new landscapes, such as estuaries and sea marshes that modify the coastline formation of Cantabria: Pas Estuary, Santander Bay, Santoña Saltmarshes, Asón Estuary and Ontón Estuary, which offer new biotopes to be exploited.The relative rise in sea level on the Basque coast during the Holocene occurred in a first stage of a rapid rise (6.3 ± 0.8 mm/year from 9000 to 7000 cal BP).The formation of the estuaries on the northern Iberian coast has been dated to about 8500 cal BP (Cearreta & Murray, 1996, p. 297).
At the same time, the higher temperatures caused the mountain glaciers at the heads of the Miera and Asón valleys to melt.In the Asón valley, the glaciers had reached down to 300 m a.s.l.The last stage in the deglaciation in the area would have occurred between 14.5 and 10 ka BP in MIS2 (Frochoso, González Pellejero, Allende Álvarez, et al., 2013).These mountain areas were freed of ice, which would compensate for the loss of territory on the coast.The importance of both environments in the economic pattern of Mesolithic societies was considerable, as observed in the use of coastal resources and in the hunting of game in the upper valleys (Pérez-Bartolomé & Muñoz Fernández, 2015) (Table 1).

Palaeovegetation
The rise in temperatures in the Holocene was accompanied by an increase in humidity on the Atlantic seaboard of Europe, which led to a rapid expansion of broadleaf forest in northern Spain (Iriarte-Chiapusso & Hernández Beloqui, 2009).Table 2 lists the pollen, anthracology, and carpology data available from sites in the study area.
Pollen studies conducted to study the transition to the Holocene, attributed culturally to the Azilian, at sites on the coastal strip (Pendo, El Perro, Fragua, and El Carabión Rock-shelter) reflect a quite dense and varied arboreal component represented by Pinus sylvestris and broad-leaf taxa Corylus and deciduous Quercus, with an increase in Betula.The shrub layer is less well represented while herbaceous plants are very abundant.
At sites in montane areas (Rascaño and Salitre), both in the Upper Miera in a humid environment, hazel dominates over pine, with the presence of Quercus and Alnus.
In the early Mesolithic, at coastal sites (Fragua, El Perro, and Las Salinas), palynological studies show the expansion of broad-leaf woodland with birch, oak, and hazel, together with typical taxa of open environments, like heather and, to a lesser extent, grasses.In the later Mesolithic level at Carabión, the   pollen reflects a decline in the arboreal layer, with the limited presence of Corylus, deciduous Quercus, and Betula, within a clear dominance of herbaceous vegetation.Anthracological studies at the Mesolithic sites of El Perro, Las Salinas, and Carabión have identified the same variety of taxa as found in the pollen record, with abundant deciduous and evergreen oak and birch.At Barcenilla, where pollen was not preserved in the Mesolithic levels, the fuel comprised oak and beech.In the montane area, at Sopeña (Miera), the remains of charred wood indicate a decline in Pinus and increase in Quercus and Corylus, although the latter may be more closely connected with the gathering and consumption of hazel nuts.In general, at all the sites, the main firewood was oak and beech.
In Level II at El Carabión, climate variations are observed in the hiatus (12.18-8.57ka cal BP).It displays the lowest biological diversity, with no representative of the arboreal layer, but the occasional presence of water had eroded the sediment.The expansion of woodland in the early Holocene in Cantabrian Spain would have increased the availability of plant resources to be foraged and of forest animals, which would compensate for the disappearance of the large herbivores owing to the environmental changes (Figure 4).

Hunting
The faunal records documented in Azilian and Mesolithic levels at the studied sites have been analysed to observe possible differences in the subsistence strategies derived from palaeoenvironmental change.The available data referring to ungulate remains are presented in Table 3 and Figure 5.
The data are only provisional as there is no information about the volume of sediment excavated at each site.In some cases, the different criteria for the quantification of osseous remain,¹ as also the lack of a study of the fauna in some sites.
The Azilian economy continued the trend in the late-final Magdalenian, based on the hunting of ungulates.Remains of red deer and ibex predominate, depending on the location of the sites and the transformation of the terrain owing to the expansion of woodland.Ibex is the most abundant species in montane areas: Rascaño and Piélago II (65%), followed by chamois in Miron (28.5%) and Piélago II (24%).Red deer is more abundant at sites in valleys: Pendo 64.7%, Carabión 55%, Morín 45%, and Mirón 40%.Roe deer, wild boar, and red deer attest the amelioration in the climate and reforestation.Important species in previous periods, like bovines and horses, gradually disappear.
In Mesolithic levels, hunting concentrated on three species: red deer, roe deer and wild boar.Red deer is the most abundant at all the sites, except at La Fragua.At El Carabión it reached 62%, (where it supplied 92% of the meat), 40% at El Mirón and 33% at Cubío Redondo.At La Fragua, wild boar (28.4%) and roe deer (21.5%) increase, as species that are well adapted to broad-leaf forests.Chamois appears in Cubío Redondo (16.6%), a site in a mountain environment, but an individual was detected at El Carabión (4.8%), which may indicate mobility towards the mountain.Pressure on ungulate has been observed because of the frequent presence of females and juveniles (38.4% in El Carabion), which indicates that specialisation in species that live in herds, especially females and young, which is not sustainable.It is also possible that hunting strategies changed and may have involved the use of traps.

Malacofauna
The use of marine resources intensified in the Mesolithic, resulting in the creation of accumulations of waste, known as "shell-middens."This is the resource that has provided most data in recent years.Table 4 presents the available data (Figure 6).The comparison of the composition of the malacofauna in the Azilian and Mesolithic levels reveals a greater accumulation and diversity of taxa in the Mesolithic levels.In Azilian levels near the coast, marine gastropods predominate.La Pila (99.7%) and El Perro (42.7%) are represented by Patella vulgata and Littorina littorea, which are cold-water species.Marine bivalves, like Mytilus, are scarcer.The case of La Fragua is exceptional, as the remains consist mainly of the continental snail Cepaea nemoralis (93.94%).
The absence of molluscs in the Azilian level at El Carabión may be related to the distance from the sea during that period, when the sea level was 60 m lower than at present.The few marine molluscs at Piélago II may have played a utilitarian role; in contrast, the deposit includes a thick shell-midden formed by the terrestrial snail Cepaea nemoralis (Vega de la Torre, 1985).Marine molluscs have not been identified at Rascaño, but Cepaea nemoralis shells are cemented to the cave wall.At Sopeña, a montane site 28 km from the coast, the malacofauna consists almost exclusively of Cepaea nemoralis (96.7%), with a small presence of Mytilus sp.(3.3%).In the Mesolithic, the use of marine gastropods continued to be intense, with frequencies that vary between 45, 60, and 90%, depending on the distance of the sites from the shore.Greatest diversity is seen near estuaries and salt marshes, with frequencies of marine bivalves higher than 50% at La Chora, Carabión, and El Perro.The foraging of echinoderms (Paracentrotus lividus) and crustaceans (Pollicipes pollicipes, Brachyura sp.) has been detected in smaller proportions.
At sites over 20 km from the shore and which are not different from the Azilian, the consumption of molluscs focused on the land snail Cepaea nemoralis with the scarce presence of Mytilus and, in some cases, Ostrea.
The species change in accordance with their climate adaptations.In the Patella genus, in Mesolithic shell-middens Patella depressa and Patella ulyssiponensis are most frequent.L. littorea is substituted by Phorcus lineatus.The contents of the shell-middens show that very small individuals were gathered.Recent studies confirm that a drop of 2°C in sea temperature in the 8.2 ka event did not influence the size of the molluscs because of their tolerance to temperature changes, and therefore this cannot have been responsible for the reduction in their size (García-Escarza et al., 2022) and this was more likely to have been caused by anthropic pressure on this resource (Álvarez-Fernández, 2007, pp. 43-58;Gutiérrez-Zugasti, 2009;García-Escarza et al., 2015, 2022).

Fishing
Few ichthyological remains are found among the fauna retrieved from the archaeological deposits, probably because of the poor state of conservation of the deposits.In the Azilian, finds of the typical flat harpoon show that fish were an important resource.Remains of fluvial species like salmon and trout have been found (Fernández-Tresguerres Velasco, 2006, p. 173).
A large diversity of fish species was identified in the Mesolithic level at Las Salinas: 6 taxa in a sample of 27 number of records.The presence of Dentex and Lithognathus mormyrus (Herrera) show that fishing took place in an estuary with warm water, corresponding to the chronology of the level.At El Carabión, the most important taxa are the mugilids (66%), which are the only fish detected in the Azilian level.Greater diversity is observed in the Mesolithic, with Anguilla, Liza, and Chelon labrosus, amphidromous estuary species.The ichthyofauna at these sites are indicative of fishing near the sites.The proportional abundance of mugilids at El Carabión can be explained by the regime of tides in the Asón estuary, where they may have been higher in the Mesolithic period.The absence of fishing utensils like harpoons and hooks, in these sites, may be a consequence of changes in technique as nets or traps may have been used.

Plant Gathering
The carpological study at El Carabión (López Dóriga, 2016) has documented in the Azilian level a fragment of charred hazel pericarp and a small fruit, possibly of Rosacea.More Rosacea and hazelnut shells were identified in the Mesolithic level, where the latter was most abundant.
The presence of hazel fragments is common at the sites.They have also been documented in Sopeña Cave and Las Salinas (Uzquiano in Pérez- Bartolomé, 2016cBartolomé, , 2019)).It is the most common plant species in proximate Mesolithic shell-middens, like La Peña del Perro (López García, López Sáez, & Uzquiano, 1996), La Fragua (Núñez de la Fuente, 2018), and El Cubío Redondo (Ruiz Cobo & Smith, 2001).Acorns have also occasionally been identified (at Las Salinas and Cubío Redondo).At El Carabión, it was noted that plants with an economic interest, but not cultivated, became more abundant in the late Mesolithic and Neolithic.
Backed bladelets are very common in Azilian assemblages and reach a proportion of 38.6% in La Pila III.3.Endscrapers, with certain diversity, predominate over burins.Geometric microliths reach 9.7% in Level I at Piélago II.Points are also quite diverse, including short and thick Azilian points at Piélago II (15%) while microgravettes predominate at Morín (28%).

Raw Materials
The most common raw material in Azilian assemblages is flint.High-quality flint predominates, including different exogenous varieties.Quartzite and quartz are very scarce and are found in pebbles used as percussors or smoothers.In Carabión Level 3, the flint varieties include Upper Cretaceous Flysch types and local Aptian flint.The flint types are similar to those studied from Piélago II, deposited in the museum of prehistory and archaeology of Cantabria: Flysch flint from the Basque coast, the Aptian type from the Miera valley, and Lower Cretaceous Urgonian flint from the marine platform at El Bocal and Rostrío (Pérez-Bartolomé, 2005 (unpublished), 2014a).
In the Mesolithic, flint from local sources predominates over 90%.Many of the pieces from Aptian outcrops are black or beige.Other types are coastal opaline and chalcedonitic flint (Lower Cretaceous Urgonian).Quartzite and sandstone were used for heavy duty tools, like hammerstones and anvils.

Osseous Industry
In the Azilian, the characteristic osseous implements are the flat harpoons, together with straight fish hooks, awls, and spear points.In the Mesolithic, osseous industry practically disappears in this part of northern Iberia; some splinters and pointed bones have been found but no fish hook has been identified.

Settlement Pattern
The Azilian population in the area of study, represented by 11 sites, follows the pattern of the late-final Magdalenian and extends from the coast (La Pila, Salinas, Fragua, El Perro) towards the interior valleys  (Valle) and mountains (Piélago, Rascaño, Salitre, Sopeña).All the deposits are located in caves.The Mesolithic population, documented at 256 sites, was generally located along the coastline, with clusters around the rias and estuaries, related to the use of littoral resources.However, the upper valleys were also occupied, following the river courses that divide up the territory and in places on a limestone substrate.Secondary valleys were equally used to exploit the new biotopes that were created with the climate improvement (Pérez-Bartolomé & Muñoz Fernández, 2015).
With the current coastline as the point of reference, the Mesolithic population in central-eastern Cantabria inhabited mainly the areas less than 1 km away (30.46%) or between 1 and 5 km (27%) and between 5 and 10 km (9%).In the interior valleys, between 10 and 20 km from the coast, the inhabitation reaches 11.71%, and in the upper valleys 20-36 km away, it is 21%.Consequently over 50% of the sites are less than 5 km from the modern coast (Pérez- Bartolomé, 2019Bartolomé, , 2021)).
At some sites, a continuity of population is seen from the late Magdalenian to the Azilian and Mesolithic (El Perro, La Fragua, La Garma A, El Mirón, Las Salinas, Sopeña, and El Carabión), and even to the Neolithic at the last four cases.However, the large caves in the interior valleys, like El Valle, the caves of Monte Castillo, Piélago and Rascaño, were abandoned.

Demography and Resilience of the Population
The population is studied taking as a reference the number of sites and the radiocarbon dates in the area of study and in Cantabrian region of Spain, in order to infer possible changes in the demography, owing to the cold pulses and the overall variations in the population (Table 7, Figure 7).wider irregular frame.The gap at Truchiro, at the base of La Garma Hill (9.4-7.9/7.4 ka cal BP), is around the 9.3 and 8.2 events.At La Fragua, these occupational hiatuses are related to the two events around 9.3 (10.2-8.4 ka cal BP) and around 8.2 (8.4-7.8 ka cal BP).The gap at El Mirón is wider (9.7-6.6 ka cal BP), and the occupations are discontinuous in the Mesolithic and of less significance.The researchers of the site explain this by an alternate use to the occupations of the coastal sites of La Fragua and El Perro (González Morales et al., 2004).At El Carabión, the hiatus between 12.7 and 8.6 ka cal BP might respond to the influence of the Younger Dryas and the 9.3 ka event; between 8.6 and 6.8 ka cal BP, the discontinuous occupation might be related to the 8.2 ka event.At Las Salinas, a site that was occupied at least from the Magdalenian, a large gap (10.8-7.8 ka cal BP) is perceived, with a later continuous occupation.The occupational gap is located in the chronology of both events.
8 Discussion and Conclusions

Palaeoenvironmental Changes
At about 11600 BP, the rapid increase in temperature led to changes in the morphology of the territory and in the vegetation.Sea level rise transformed the coastline as the river valleys were flooded, creating estuaries and salt marshes.At the same time, as the mountain glaciers in the upper Asón and Miera valleys melted in 14.5 to 10 ka BP (Frochoso et al., 2013), new land surfaces were reforested which provided plant and animal resources.
In the early Holocene, the rise in temperature and humidity allowed an expansion in the percentages of arboreal pollen, as identified at Azilian sites on the coast (Salinas, Fragua and El Perro) as the steppe vegetation and pine forests were replaced by mesophile broad-leaf woodland.The pollen remains from the Azilian levels of sites located in the high inland valleys, Salitre (López García, 1981) and Rascaño (Boyer-Klein, 1981), show an increase in the taxa of oak and hazelnut trees, which are replacing the pine forests.
Mixed deciduous forest was fully established in the littoral area by 8.6 ka BP.Depending on the location of the sites, deciduous oak was dominant over other mesophile trees at Mesolithic sites, together with holm oak, ash, beech, and the shrub and herbaceous layers (Carabión, Las Salinas).The evolution of the vegetation in interior and montane areas was similar.Quercus and mesophile trees, especially Corylus and Fraxinus, were the most characteristic taxa in the middle Holocene.
At El Carabión, about 8.5 ka BP, the arboreal layer began to decline and herbaceous layer clearly dominated.This might be related to the abrupt climate events in about 8.6-8.5 ka cited earlier.The same decrease in forest mass has been identified on the western coast of the Cantabria region, at El Mazo (Asturias).At this site, which covers the chronological period around the 8.2 ka event, arboreal pollen decreases apart from Pinus and Betula, indicating cooler temperatures in (8176-8021 cal BP).This is attributed to greater aridity at that time.The arboreal layer expands again in 8004-7792 cal BP, with a dominance of Corylus, Quercus, and Betula (Núñez de la Fuente, 2018, pp.88-89).

Changes in the Economic Pattern
The Azilian economy is based on hunting ungulates and gathering terrestrial vegetables and molluscs.In the Minimum number of individuals of hunting provided by 7 Azilian sites in the study area, it can be seen that deer is the most frequent taxon in the sites on the coast and coastal plain: El Pendo I (64.7%),Morín (45.5%),El Perro 2 A/2B (28.6%) and El Carabión III (55%).In the settlements located in inland valleys and mountain areas, goat hunting predominates: in Rascaño and Piélago II it contributes 65%, followed by deer and chamois (24%).El Mirón provided variable frequencies of goat in the different levels, from 50% in level 11 to 16.7% in level 102.2 (Table 3).Bovids and equids gradually disappear and wooland species like roe deer and wil boar increase.
Little information is available about hunting in the Mesolithic.Red deer is the most frequent prey in almost all the sites investigated: Carabión (62%), Barcenilla (25%), and Cubío Redondo (33.3%).Wild boar is more frequent in La Fragua (28.4%) and also roe deer and goat (both 21.5%).Reforestation favoured the species to adapt to broad-leaf forest, like roe deer and wild boar.Hunting of roe deer and smaller species such as carnivores has also been documented.
Pressure on the prey has been determined in the Mesolithic, through the abundant remains of females, neonates, and juveniles (the latter reach 38.5% at El Carabión).The decline in the number of ungulates has been attributed to the demographic increase (Estévez, 2005;Marín-Arroyo & González-Morales, 2009).
Molluscs were an important complement in the diet.In the early Holocene, in the Azilian, the consumption of molluscs at sites on the coast included cold-water species like Patella vulgata and L. littorea.La Fragua is an exception because the terrestrial snail was gathered most (Gutiérrez-Zugasti, 2009, p. 240).
In the inland valleys and mountain areas, marine molluscs were consumed less in the diet, which was complemented by the terrestrial gastropod Cepaea nemoralis, very abundant in Level 2 of Piélago II (Vega de la Torre 1985: 123-126).Numerous shells of land snails concreted in the upper Azilian level are found at Rascaño, and at the Salitre site in the same Miera valley (Pérez-Bartolomé 2005 unpublished).In Sopeña, located 28 km from the coastline, the malacofauna is composed almost exclusively of Cepaea nemoralis (99%) together with Mytilus sp.(1%).In the Azilian, these sites were located further from the sea, as the coastline was at -65 m (Gutiérrez-Zugasti, 2009: p. 78).
The consumption of molluscs increases in the Mesolithic, when marine gastropods were exploited intensely, particularly near the coast.Owing to the formation of estuaries and salt marshes, the number of bivalves and the diversity of molluscs increase: this is the case of the Mogro Estuary, Bay of Santander, and the Asón Estuary.Further from the shore, the consumption of molluscs continued to focus on Cepaea nemoralis, with some Mytilus and occasionally Ostrea.
The rise in sea water temperature is perceived in the replacement of L. littorea by P. lineatus.In the Patella genus, P. vulgata decreases and P. depressa and P. ulyssiponensis increase in representation.
The impact of the 9.3 ka BP event has been detected in the gathering of molluscs in the west, at El Mazo, in SU 108 (c. 9 ka BP), whereas more temperate conditions reigned in units 114 and 115 (c.8.8 ka cal BP).The 8.2 ka event was identified in SU 105 (c.8.4 ka cal BP) immediately before this cold pulse (García-Escarza, 2022).The reduction in the size of shells at that time observed at El Mazo (García-Escarza et al., 2022) does not seem to be related to natural processes.Therefore, although the TSM influenced the diversity of species, the main cause for the decrease in shell size appears to have been anthropic pressure.Conversely, the ecological knowledge of the last hunter-gatherers allowed them to apply sustainable management strategies in which the reduction in the size did not go beyond limits regarded as acceptable.
Fishing is well documented in the Azilian by the frequency of flat harpoons and bi-pointed hooks, even though ichthyological remains are not abundant.Freshwater fish like salmon and trout have been documented (Fernández-Tresguerres Velasco, 2006).Only two remains of Mugilidae were identified at El Carabión, with greater diversity in the Mesolithic level, which indicates intensification in this resource.At Las Salinas, nearer to the coast, there is a greater diversity of marine species caught in the littoral zone of the estuary, in warm wáter: Dentex and Lithognathus mormyrus (Herrera).This indicates intensification in the use of aquatic resources.
Plant gathering has been documented very little owing to the poor preservation of plants and perhaps because of the excavation methodologies.The consumption of hazelnuts, Rosaceae, and acorns has been attested in Mesolithic deposits.
In the Holocene, a broad spectrum diet included a wide array of resources available in the new biotopes.This may have been due to demographic pressure, partly because of the change towards sedentism, partly because of the change in the vegetation, and perhaps also because of competition in the procurement of resources, like prey, which are limited in the territory.Regarding the relative role of terrestrial and marine resources in the diet of Mesolithic hunter-gatherers, a recent study (Portero, Cueto, Fernández-Gómez, & Álvarez-Fernández, 2022) at sites in the Cantabria region, particularly La Fragua and El Carabión, verifies that in general terms, ungulates would have provided a greater amount of meat and fats, amounting to 84.5% of the total calories consumed, and molluscs 5.4% of the calories.

Changes in Industry
The classic Azilian assemblages are characterised by a very marked increase in backed bladelets, endscrapers, and geometric microliths, which are predominant in the whole Cantabrian region and amount to over 50% (Fernández-Tresguerres Velasco, 2006).In the Azilian levels studied here, backed bladelets dominate with percentages over 38% in El Perro and La Pila III.3.Endscrapers are generally common, between 13.6% in Morín and 40% in El Perro Level 2b.At Piélago II (Azilian 3), points appear in a high proportion (24.55%).At these sites, geometric microliths are less abundant than what is generally found in the region.The highest percentage is found in Piélago II, Level I (9.68%).The decrease in the frequency of blades and increase in bladelets mean that the typology of Azilian assemblages is smaller.
In Mesolithic levels, the indices of endscrapers, denticulates, and notches remain high.The index of geometric microliths at La Garma A is 1.3%.In the rest of the sites with few lithic assemblages and a reduced number of microliths, the indices seem to be high: Las Salinas (9%) and Barcenilla (levels V-X) 22%.No geometrics were found in the Mesolithic level at El Carabión.The high frequency of flakes in the Mesolithic levels may indicate the use of composite points for hunting tools.In general, the diversity of lithic typology in the Mesolithic is low.
Comparing the typology indices of both Azilian and Mesolithic levels, the indices of burin, dorsal, and points are higher in the Azilian levels.Within the typological groups, there is greater variability in the Azilian in the types of scrapers, burins, and points.
Flint is the most usual raw material at Azilian and Mesolithic sites, with a predominance of high-quality distant varieties in the former period and local types at the end of the sequence.In the Mesolithic, Lower Cretaceous Urgonian flint was acquired on the coast at distances of less than 5 km.Quartzite and sandstone were used for large implements like percussors and anvils.
In osseous assemblages, flat harpoons, bi-pointed hooks, awls, and spatulas are abundant in the Azilian.In the Mesolithic, the osseous industry practically disappears, except for bi-pointed hooks, which have not been found at the sites studied here.Pierced batons have been documented in the west of the region at Fonfría, Tres Calabres, and Los Canes (Asturias) and in the Basque Country at Logalán, Santimamiñe, and Herrico Barra.
In accordance with the simplified technology, a change in hunting and fishing strategies can be perceived, and perhaps traps and palisades were used, as indicated by the hunting of female and neonate animals and smaller fish.

Demography and Resilience of the Population
The study of the dates and sites has been made with deposits that have been investigated and/or dated.The archaeological record of sites with a Holocene shell-midden, documented by surveying, is much larger with 256 sites known in central-eastern Cantabria (Pérez-Bartolomé, 2019).In the western side of the Cantabrian region (Asturias and west Cantabria), a large number of shell-middens are known: 100 sites in west Cantabria (Pérez-Bartolomé & Muñoz Fernández, 2013) and 167 sites in Asturias (Fano Martínez, 1998).Recent surveying projects in Asturias have catalogued new shell-middens, increasing the register to 293 (Pérez- Bartolomé, Muñoz Fernández, & Fanjul Peraza, 2018a,b).
The databases with 14 C results may reflect a partial view of the archaeological reality, which is limited by diverse circumstances: the erosion that has removed a large part of many deposits, the differential conservation of remains, or variable intensity of research.While a very large number of deposits is known, others in the open air may have disappeared or not been detected.However, we can deduce a sociocultural reality that was surely rich and diverse in solutions, able to make use of all the resources in their surroundings, and overcome the difficulties that climate variations caused, which would have been challenging considering how much the hunter-gather groups depended on the environment.
The oscillations perceived in the radiocarbon dates reflect the decrease in the Azilian population c. 11.6 ka, which might have been caused by the Younger Dryas.The 9.3 and 8.2 ka events, identified in stalagmites and sea water, with lower temperatures, affected mollusc species and allowed an increase in cold-water species like P. vulgata while warmer-water species (P.depressa, P. ulyssiponensis and P. lineatus) decreased in number, as detected in the shell-midden of El Mazo (Asturias).This does not seem to have influenced the occupation of the site as a large number of dates cover the time span of 9009-8004 cal BP (García-Escarza et al., 2015, 2021).The drop in temperature in about 8.4 ka in SU 105 would be before the 8.2 ka event, which seems to confirm the variation or length of the event, as stated previously.These oscillations perceived in the population are coherent with the phases in the population dynamic proposed from Cantabrian Spain (Fernández-López de Pablo et al., 2019).
The decrease in the pollen identified at sites in about the 8.2 ka event reflects the consequences for the vegetation and fauna, and therefore in the gathering of plants by the human groups, as seen in the consumption of species of little economic interest.This may have influenced the demographic reduction.At El Carabión, the arboreal mass decreased at the end of the sequence, but this may be related to the encouragement of plants with an economic interest by the human groups.
The population overcame the environmental changes which, according to researchers, may not have been too extreme in the Cantabrian region because of the ameliorating influence of the ocean on the coastal area.Cantabrian Spain has often been considered a refugium for the population during the coldest periods in the Palaeolithic; also, in the Holocene groups may have emigrated towards the north and brought the geometric microliths that became more abundant after the 8.2 ka event.
Recent DNA studies have found evidence of genetic flow from outside at the end of the Ice Age.The Villabruna group has been identified at El Mirón in about 14 ka, and this flow may have advanced in the Younger Dryas and early Holocene.It became the dominant group in the later and final Mesolithic in Cantabrian Spain, and has been detected at Los Canes (Arangas, Asturias) c. 7.1 ka (Fu et al., 2016).

Conclusion
Although the 9.3 and 8.2 ka cold events have been identified in the palaeoenvironmental record and in the reduction on the number of radiocarbon dates around the time of the events, they do not seem to have affected the population too greatly.The gradual overall growth in the population through the Azilian and Mesolithic shows the great resilience and capacity for socioeconomic and technological adaptation of the inhabitants of the region, who diversified and exploited fully the different resources available in their immediate surroundings.Nor did they need to migrate, but remained in the territory, probably with temporary internal movements as they advanced towards a process of sedentism.

Figure 1 :
Figure 1: Cantabrian region (N.Spain) Delimitation of the Mesolithic area in central-eastern Cantabria, with location of the archaeological sites cited in the text.

Figure 2 :
Figure 2: Topographic map of Cantabria showing the location of Mesolithic settlements in central-eastern Cantabria, between the Suances estuary to the west and the Ontón estuary to the east, located on the coastline, coastal plain, and associated with inland and high valleys.

Figure 3 :
Figure 3: Carabión rock-shelter: stratigraphic profile north of the test pit, squares C5-(D5 Sectors 3.6) with indication of the levels and their radiocarbon dates.
Very fine greyish ochre loose soil with very crushed snail debris (30 cm) Shell-midden of Cepaea n.

Table 5 :
Frequencies of lithic typology in the Azilian of central-eastern Cantabria

Figure 8 :
Figure 8: Development of Mesolithic population in the study area, central-eastern Cantabria, compared to Mesolithic settlement in the Cantabrian Region (N Spain) between 9.5 and 7.9 ka cal BP.

Table 1 :
Archaeological contex information of sites: stratigraphy, description of main archaeological items, and cultural record

Table 1 :
(Weninger et al., 2007)sites in central-eastern Cantabria analysed in this article, along with a description of stratigraphies, archaeological remains and radiocarbon dating.Calibration program: CalPal(Weninger et al., 2007)version.

Table 2 :
Palaeovegetation: pollen and anthracological component relationship of early and middle Holocene deposits

Table 4 :
MNI of mollusc in Azilian and Mesolithic sites in central-eastern Cantabria

Table 6 :
Frequencies of lithic typology in the Mesolithic of central-eastern Cantabria

Table 7 :
Radiocarbon dates of archaeological levels from Mesolithic sites in the Cantabrian region (N Spain)