A Middle Palaeolithic wooden digging stick from Aranbaltza III, Spain

Abstract

Aranbaltza is an archaeological complex formed by at least three open-air sites. Between 2014 and 2015 a test excavation carried out in Aranbaltza III revealed the presence of a sand and clay sedimentary sequence formed in floodplain environments, within which six sedimentary units have been identified. This sequence was formed between 137–50 ka, and includes several archaeological horizons, attesting to the long-term presence of Neanderthal communities in this area. One of these horizons, corresponding with Unit 4, yielded two wooden tools. One of these tools is a beveled pointed tool that was shaped through a complex operational sequence involving branch shaping, bark peeling, twig removal, shaping, polishing, thermal exposition and chopping. A use-wear analysis of the tool shows it to have traces related with digging soil so it has been interpreted as representing a digging stick. This is the first time such a tool has been identified in a European Late Middle Palaeolithic context; it also represents one of the first well-preserved Middle Palaeolithic wooden tool found in southern Europe. This artefact represents one of the few examples available of wooden tool preservation for the European Palaeolithic, allowing us to further explore the role wooden technologies played in Neanderthal communities.

Full text

RESEARCH ARTICLE
A Middle Palaeolithic wooden digging stick
from Aranbaltza III, Spain
Joseba Rios-Garaizar
1
*, Oriol Lo
´pez-Bulto
´
2
, Eneko Iriarte
3
, Carlos Pe
´rez-Garrido
4
,
Raquel Pique
´
2
, Arantza Aranburu
5
, Marı
´a Jose
´Iriarte-Chiapusso
6,7
, Illuminada Ortega-
Cordellat
8
, Laurence Bourguignon
8
, Diego Garate
9
, Iñaki Libano
10
1Centro Nacional de Investigacio
´n sobre la Evolucio
´n Humana (CENIEH), Burgos, Spain, 2Department of
Prehistory, Universitat Autonoma de Barcelona, Barcelona, Spain, 3Laboratorio de Evolucio
´n Humana,
Universidad de Burgos, Burgos, Spain, 4Departamento de Cristalografı
´a y Mineralogı
´a, Facultad de
Geologı
´a, Universidad Complutense de Madrid, Madrid, Spain, 5Departamento de Mineralogı
´a y Petrologı
´a,
Facultad de Ciencia y Tecnologı
´a, Universidad del Paı
´s Vasco/EHU, Leioa, Spain, 6Departamento de
Geografı
´a, Prehistoria y Arqueologı
´a, Facultad de Letras, Euskal Herriko Unibertsitatea UPV/EHU, Vitoria-
Gasteiz, Spain, 7IKERBASQUE, Basque Foundation for Science, Bilbao, Spain, 8INRAP, UMR 7041
Arscan/AnTet, Campagne, France, 9Ramo
´n y Cajal Senior Grant, Instituto Internacional de Investigaciones
Prehisto
´ricas de Cantabria, Universidad de Cantabria, Gobierno de Cantabria, Santander, Spain,
10 Edestiaurre Arkeologia Elkartea, Barrika, Spain
*joseba.rios@cenieh.es
Abstract
Aranbaltza is an archaeological complex formed by at least three open-air sites. Between
2014 and 2015 a test excavation carried out in Aranbaltza III revealed the presence of a
sand and clay sedimentary sequence formed in floodplain environments, within which six
sedimentary units have been identified. This sequence was formed between 137–50 ka,
and includes several archaeological horizons, attesting to the long-term presence of Nean-
derthal communities in this area. One of these horizons, corresponding with Unit 4, yielded
two wooden tools. One of these tools is a beveled pointed tool that was shaped through a
complex operational sequence involving branch shaping, bark peeling, twig removal, shap-
ing, polishing, thermal exposition and chopping. A use-wear analysis of the tool shows it to
have traces related with digging soil so it has been interpreted as representing a digging
stick. This is the first time such a tool has been identified in a European Late Middle Palaeo-
lithic context; it also represents one of the first well-preserved Middle Palaeolithic wooden
tool found in southern Europe. This artefact represents one of the few examples available of
wooden tool preservation for the European Palaeolithic, allowing us to further explore the
role wooden technologies played in Neanderthal communities.
Introduction
The production and use of wooden tools in the European Late Lower-Early Middle Palaeo-
lithic has been indirectly attested through use-wear analyses [1–4], but direct evidence is much
more scarce, most likely due to preservational biases, and only a few sites above latitude 48
have yielded preserved wooden tools (Scho¨ningen, Lehringen and Clacton) [5–8]. The site of
Bad-Cannstatt, in Germany, has also yielded maple (Acer campester) fragments interpreted
as tools, but theses remains were heavily altered and thus are difficult to interpret [9].
PLOS ONE | https://doi.org/10.1371/journal.pone.0195044 March 28, 2018 1 / 15
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OPEN ACCESS
Citation: Rios-Garaizar J, Lo
´pez-Bulto
´O, Iriarte E,
Pe
´rez-Garrido C, Pique
´R, Aranburu A, et al. (2018)
A Middle Palaeolithic wooden digging stick from
Aranbaltza III, Spain. PLoS ONE 13(3): e0195044.
https://doi.org/10.1371/journal.pone.0195044
Editor: Marco Peresani, Universita degli Studi di
Ferrara, ITALY
Received: October 9, 2017
Accepted: March 15, 2018
Published: March 28, 2018
Copyright: ©2018 Rios-Garaizar et al. This is an
open access article distributed under the terms of
the Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Funding: The archeological work at Aranbaltza site
is financed by the Diputacio
´n Foral de Bizkaia
(2147/2013; 1602/2014; 2396/2015; 1518/2016;
1797/2017), the Basque Government (Gobierno
Vasco: 2015/04424; 2014/03867). The funders had
no role in study design, data collection and
analysis, decision to publish, or preparation of the
manuscript.

Interestingly, most of these wooden tools have been interpreted as throwing and thrusting
spears. This is the case for the Lehringen spears, for the Clacton spear fragment and for most
of the tools recovered in Scho¨ningen. Most of these tools were made on Taxus baccata (yew,
Clacton and Lehringen) and Picea sp. (spruce, Scho¨ningen), with some examples on Pinus syl-
vestris (pine, Scho¨ningen). The technology required to produce these spears was quite com-
plex: to begin with, a long and thin shaft was selected, the bark and the knots were removed
and the point, usually placed away from the central axis of the trunk, was obtained through
scraping and polishing, maybe aided by fire [10]. Some authors have argued that this kind of
tool production represents a significant cognitive leap for hominids because the complexity
involved in the process implies abstraction and in-depth planning capacities [11]. Others, on
the other hand, have argued that the wooden tool-making process might have been far more
simple than is currently thought [12]. Besides, other kinds of wooden tools have been also
identified, but are less abundant, among them the pointed stick from Scho¨ningen [6]. In
southern Europe the only direct evidence of wooden tools predating modern human arrival
are the wooden artefacts from Abric Romanı
´and the recently discovered sticks from Poggetti
Vecchi. At Poggetti Vecchi more than 30 fragments interpreted as sticks have been recovered
from a MIS7-6 open air context [13,14]. At Abric Romanı
´putative tool functions have been
inferred from the morphologies of the wooden artefacts, including objects interpreted as ves-
sels or shovels [15–16. One single wooden pseudomorph from Abric Romanı
´level J has been
interpreted as a possible digging stick or fragment of a stake [17].
Here we present a wooden pointed tool found at Aranbaltza III (Basque Country, northern
Spain) dated to the early Late Pleistocene, which represents the oldest wooden tool from south-
ern Europe, in this case associated with Neanderthals.
Archaeological setting
The site of Aranbaltza is located in the coast of Basque region, close to Bilbao. The site is situ-
ated in the bottom of a small valley that runs towards the Butron river-mouth. Although the
current coastline is very close to the site (800 m NW) it is separated from the site by a raised
cliff (90 m.a.s.l). The site was discovered in 2004 [18], close to the site of Ollagorta, where in
1959 J.M. Barandiaran excavated several test-pits in the front area of a sand quarry [19]. Since
2013 archaeological excavations at the Aranbaltza complex have identified three archaeological
sites (Aranbaltza I, II and III) (Fig 1) with comparable archaeo-sedimentary sequences span-
ning from the Late Middle Pleistocene all the way to the Holocene.
At Aranbaltza III a 2m
2
test pit was excavated between 2014 and 2015 (UTM 30N x:
502713.6, y: 4805178.6, z: 37). As part of this excavation, a total of six lithostratigraphic units
and four sedimentary facies were defined (Fig 2) (S1 File). From top to bottom:
•Unit 0 represents modern reworked sediments.
•Unit 1 is a channel sandy infill with a basal lag where abundant Mousterian lithic remains
were found (S2 File).
•Unit 2, which is archaeologically sterile, has been interpreted as representing an incised
channel infill consisting of multiple sandy high density flowing events, extensively altered by
edaphic processes (podzolization).
•Unit 3 is made up of bioturbated floodplain clays and, as the previous unit, is archaeologi-
cally sterile.
•Unit 4 is a thick sand deposit interpreted as representing a tractive sandy sediment sheet
formed in a crevasse splay/channel; In this unit two wooden tools and a single flint tool (see
Middle Palaeolithic wooden digging stick from Aranbaltza III
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Competing interests: The authors have declared
that no competing interests exist.

Fig 1. (top) location of the Aranbaltza archaeological complex; (bottom) position and extension of the different excavation areas. Raster data
obtained from Eusko Jaurlaritza / Gobierno Vasco. GeoEuskadi and from the European Environment Agency. Rivers and bathymetry vectors
obtained from Natural Earth. Map elaborated with QGIS 2.8 Wien and Inkscape 0.91.
https://doi.org/10.1371/journal.pone.0195044.g001
Middle Palaeolithic wooden digging stick from Aranbaltza III
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S2 File) were recovered. One of the wooden tools is the point described here (S5 File), the
other one is a fragment of a pulled out branch that preserves part of the ripped joint with the
parent trunk, having the distal end intentionally pointed (S6 File). Both tools were found in
almost vertical position inside the sandy sediment, and both of them bear abrasion traces
caused by sand in movement, as does the flint tool recovered with them. This suggests that
the pieces were not in situ but reworked from stratigraphically older lateral deposits (proba-
bly Unit 5).
Fig 2. Lithostratigraphic panel and synthetic stratigraphic column of the Aranbaltza III site. The locations of wooden remains, OSL, pollen and sedimentological
samples are noted.
https://doi.org/10.1371/journal.pone.0195044.g002
Middle Palaeolithic wooden digging stick from Aranbaltza III
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•Unit 5 consists of interbedded decimetre-scale layers of grey-to-blackish sandy organic
muds (subunits 5a and 5c) and clayey sands (subunits 5b and 5d) deposited in a vegetated
backswamp area where sandy sediments were deposited during flood events (crevasse chan-
nels or lobules); this unit is rich in lithic artefacts (S2 File) and unworked wood remains.
•Unit 6 is an incised channel infill corresponding to multiple sandy high-density flowing
events, and it is archaeologically sterile.
Lithostratigraphical units 1, 2, 4 and 6 correspond to different types of fluvial channel infill-
ings, the former and latter are probably laterally migrating shallow channels, while Unit 2 cor-
responds to an incised channel infill consisting of multiple sediment gravity flows. The lower
lithostratigraphic units, (3, 4 and 5), are interpreted as representing overbank fine architectural
elements, deposited in floodplain environments. The observed lithofacies were deposited in
crevasse splay and backswamp environments. Units 2, 3, 4 and 6 have been dated by OSL (S3
File). Despite the problems of differential bleaching of quartz grains, the sequence can be
dated confidently between ca. 137–50 ka. The Minimum Age Model for Unit 4 yielded an age
of 70.0±8.4 ka.
The pollen analysis carried out for Unit 4 suggests a formation under relatively temperate
and humid conditions. The dynamics of Gramineae, heathers and Compositae (main compo-
nents of the herbaceous-shrub layer), alongside the diversity of hydrophyte and vascular
aquatic plants (Ranunculaceae, Cyperaceae, Liliaceae, Typha and Potagometon) and bryo-
phytes like Sphagnum suggest the presence of a waterlogged environment. Tree cover (circa
40%) is dominated by conifers (>70%) and mixed deciduous forest. Among the latter, Taxus
pollen has been identified.
Methods
The wooden pointed tool recovered at Aranbaltza III, is analyzed here. A morphological
description, an anatomic and taxonomic classification, a technological analysis and a use-wear
analysis will be presented.
The piece became deformed as a result of the preservation procedures, including shrinking
and bending. The original morphology of the piece was reconstructed using virtual restoration
procedures comprising photos of the piece obtained at the moment of its discovery and the
surface scans made taken with an Artec Spider scan (S4 File,S5 File). The morphological and
metric description was made using this restored model and the actual piece, which, thanks to
the preservation techniques employed, shows very well preserved surfaces.
The external morphology and the internal structure of the piece were analyzed in order to
classify it anatomically. The internal structure analysis was carried out by means of a MicroCT
scan of the piece. The sample was scanned using a 240 kV X-ray tube working at 50 kV and
100 μA, producing 1200 radiographs at a 27 μm resolution.
For the taxonomic classification, a small splint of wood was extracted from the surface that
was damaged during excavation, and the identification was made through its microscopic
analysis and comparison with a reference atlas [20].
For the technological analysis, the morphometric and anatomic features were considered
(for example the position of the central pitch), and the technological wear observed on the sur-
face was characterized and compared against already-available descriptions [6,8] and experi-
mentally-reproduced wooden tools [21]. The undertaking of a high power use-wear analysis
was not possible due to preservation issues, but a low-power analysis was carried out in order
to obtain direct insights on tool-function [21].
Middle Palaeolithic wooden digging stick from Aranbaltza III
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The wooden pointed tool
The point was recovered during the section cleaning of Unit 4 and, as a result, suffered some
damage to one of its sides. The pointed tool was initially photographed and then stored in a
watertight container alongside the original sediment in which it was found. The microscopic
analysis of a small fragment recovered from the damaged area has allowed us to identify the
tree species from which it was made: yew (Taxus baccata) (Fig 3). The presence of this species
in the surroundings of the site was also identified in the pollen analysis. Although this species
has rarely been identified in Pleistocene archaeological contexts [22], it was used to make the
spears found at Clacton-on-Sea and Lehringen [5,6]. In the Iberian Peninsula only a few yew
charcoal remains have been identified for this period, at the Middle Palaeolithic site of Can
Costella [23] (northeast Iberian Peninsula). Yew is highly appreciated in woodworking because
its wood is hard, flexible and rot-resistant; it has been used traditionally to make spears and
bows [24].
The original morphology of the piece was a straight stick 151.7 mm in length and 28.6 mm
in width, with an irregular or slightly oval transversal section, with a pointed distal end
(rounded U-shape) and a beveled proximal part (Fig 4). One third of the surface corresponds
to the sub-cortical part of a big branch, with small twig knots on it. The growing direction of
the twigs is towards the pointed end indicating that the beveled end was the closest to the
roots. The internal structure of the point, more precisely the growing rings, reveals that
towards the base the centre of the branch is located close to the lateral surface, while the point
is placed far away from the central axis of the branch (Fig 5). Half of the diameter of branch is
preserved at the base, while only a fraction of it is preserved in the point area. The piece does
not show bark or inner bark.
The surface shows little technological evidence of chopping and shaping (Fig 6). Only two
small cut-marks, corresponding with the latest phases of shaping, have been noted on the sur-
face. The twig knots do not show any wear linked to trimming using a cutting edge, thus we
could interpret these as having simply been pulled off (Fig 6B). The surface is polished (Fig
6D), which could probably explain the absence of other manufacture traces; nevertheless we
were not able to rule out the possibility that this polish was the result of an alteration caused by
the contact with the sandy sediments of Unit 4. Also, the surface shows important colouration
changes, with reddish and blackish tones (Fig 6C), suggesting that the point underwent a ther-
mal alteration, maybe as a result of its hardening and/or shaping through the use of fire [10,
14]. The bevel on the proximal end reveals a rough surface, with exposed fibres and two
Fig 3. Tree species identification. a) CT scan image of the transversal cross-section; the distinct growth rings of a coniferous wood can be seen. b)
Longitudinal-tangential cross-section, rays between 6 and 11 cells high can be distinguished. c) Longitudinal-radial cross-section, spiral thickenings on
the tracheid walls can be observed.
https://doi.org/10.1371/journal.pone.0195044.g003
Middle Palaeolithic wooden digging stick from Aranbaltza III
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different planes, suggesting that it was chopped by means of two strokes (Fig 6E and 6F). The
surface of the bevel does not show traces of polishing. These differences in the surface could
suggest that the bevel was shaped after the point was finished and used. This would mean that
Fig 4. The wooden pointed tool. a) Photograph showing the pointed tool immediately following its recovery. b) Current appearance of the point
fragment following preservation efforts.
https://doi.org/10.1371/journal.pone.0195044.g004
Fig 5. Selected MicroCT slices. The red dots indicate the actual or estimated position of the centre of the branch.
https://doi.org/10.1371/journal.pone.0195044.g005
Middle Palaeolithic wooden digging stick from Aranbaltza III
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this is a recycled tool fragment, but we cannot rule out that this simply represents a different
technological treatment of different parts of the same tool.
Fig 6. Technological and use wear features. a) Detail of the smashed fibres in the point 1: Aranbaltza pointed stick, 2: experimental pointed stick with
smashed fibres on its pointed end [21]; b) detail of the pulled-off twig knot; c) detail of the thermal alteration 4: red colouration, 5: black colouration; d)
microscopic detail of the polished surface; e) detail of the beveled end with the two plans corresponding to the two chopping strokes; f) small cut mark
on the wood surface.
https://doi.org/10.1371/journal.pone.0195044.g006
Middle Palaeolithic wooden digging stick from Aranbaltza III
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Finally, the point shows that the smashed fibres on its end were caused by some kind of
repetitive mechanical stress only affecting that particular area (Fig 6A1). This kind of wear has
been identified on Neolithic wooden pointed digging sticks at the site of La Draga [18], and
the experimental replicas of these digging sticks demonstrate that this kind of use-wear is
produced when removing medium-to-hard soil (Fig 6A2). Similar use-wear has also been
recorded on the wooden tools identified as digging sticks at the site of Border Cave (South
Africa) [25]. The Aranbaltza point tip also has a rounded (U-shaped) morphology, while the
spear points recovered from Middle Pleistocene sites in Northern Europe have sharper
(‘pointed’) tips. Thus, the morphology and the use-wear of the Aranbaltza point suggests that
it was used as a digging stick.
Although the preservation of the piece does not allow for a precise description of the opera-
tional sequence to be put forward, we are able to identify a combination of operations, includ-
ing branch shaping, bark peeling, twig removal, shaping, (probable) polishing, thermal
exposition and chopping. The available evidence suggests that, as was the case with the Scho¨-
ningen and Lehringen spears [6,8], a whole branch or a thin trunk was used and the point end
was placed away from the central axis. Evidence of use has also been identified suggesting that
this artefact was used in a mechanical activity, like digging. Due to the short length of the point
the idea that the preserved point is a recycled fragment of a bigger tool cannot be ruled out.
Discussion
The finding of wooden artefacts in Pleistocene archaeological sites in Europe is exceptionally
rare. Up to now few well-preserved artefacts have been recovered from Middle Pleistocene
deposits in Northern Europe, and few more from Upper Pleistocene sites [5–8,14–16]. The
preservation in Aranbaltza III was favoured by the formation of a waterlogged reducing depo-
sitional environment due to the rapid sedimentation of organic-rich sands and clays in a flood-
plain swampy area. The wooden point fragment was found in a sandy and slightly tractive
deposit (Unit 4), and was probably reworked from nearby exposed underlying sediments from
Unit 5, where favorable conditions for wood preservation and the presence of wooden remains
have been confirmed. The age of these deposits ranges between 58–137 ka, this apparently age
incertitude can be explained by the insufficient bleaching of quartz sand grains due to the
nature of their sedimentary processes, which implied quick erosion and deposition at a short
distance from the original sediment. The age obtained from the sandy sediments contempora-
neous with or younger than Unit 5 in another sector of Aranbaltza III was ca. 90 ka, which
could be interpreted as the most probable age for the pointed tool. The lithic assemblages
recovered from Units 4 and 5, albeit scarce, point clearly to the Middle Palaeolithic with Dis-
coid technology. Middle Palaeolithic occupations in the region are known since MIS7-6. Sev-
eral sites have occupations dated to the MIS5-4 interval, with Arlanpe, Lezetxiki or Askondo as
the most relevant [26–28]. The Early and Late Middle Palaeolithic in the region are character-
ized by great behavioural variability; the long-distance transport of lithic raw materials [29],
the trend towards microlithization [30], the use of complex hunting technologies [31], the fire
control and use [32], use of bone tools [33,34], a certain degree of prey specialization [35] or
the exploitation of marine resources [36] being especially remarkable. We should now add
elaborate wooden technology to this behavioural complexity, drawing a picture of well-
adapted and flexible Neanderthal populations in the region.
The oldest wooden tools, recovered at Scho¨ningen and Clacton, are associated with Lower
Palaeolithic industries, and reveal an early use of wooden artefacts for hunting and other activ-
ities [5–7]. The wooden sticks from Poggetti Vecchi have been dated to MIS7-6, and thus can
be also associated to Neanderthals. The function of these objects, inferred from their
Middle Palaeolithic wooden digging stick from Aranbaltza III
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morphologies, has been interpreted as digging sticks [14]. The spear from Lehringen was
recovered in a sedimentary deposit dated to ca. 125.000 BP, and thus, is associated with Nean-
derthals [8]. This tool has been interpreted as a thrusting spear, similar to the spear VI from
Scho¨ningen, while other spears from Scho¨ningen have been interpreted as throwing spears [6].
At Abric Romanı
´several wooden pseudomorphs were reported in levels H, I, Ksup and M,
dated to the Late Middle Palaeolithic [15–16,37].
The few available direct and indirect lines of evidence suggest that wood played a significant
role in Neanderthal technological adaptations. Wood provides enough plasticity to shape a var-
ied array of tools that are impossible to obtain through the use of stones, and very difficult to
obtain with bones, which have constrained sizes and are more difficult to work. The use of bone
technology by Neanderthals has been widely demonstrated, but the extent of activities identified
is, up to now, very limited and linked to domestic activities (polishers, chisels, retouchers) [33–
34,38–43]. Wood was surely used for manufacturing hunting weapons and as fuel [37,44].
Other functions, as containers, hammers, or shelter construction materials, should not be ruled
out even if the evidence is very scarce or completely absent [15,45]. Different stone-tool types
that have woodworking-related use-wear or tools that must have necessarily been used with a
wooden haft (e.g. stone spear-points) are indirect evidence of wood use in the past [30,46–52].
This paper has presented a new Middle Paleolithic wooden tool. The shape of this tool and
the evidence of use suggest its function as digging instrument. Digging stick is a common tool
in hunter gatherer societies, being root digging one of the main functions [53–56], although
other uses as loosening bark or clam-digging have been also recorded.
The variability in shape and dimensions in archaeological and ethnographical digging sticks
is enormous. According to Oswalt [55] digging-sticks are multi purpose tools and probably
this explains the high morphological variability of ethnographic digging sticks. For example,
the measures of ethnographic materials from Australian collections recorded by Nugent ranges
between 420x30 mm to 1684x33 mm [57]. Similar variability has been recorded in ethno-
graphic databases [58–59].
The length of Aranbaltza point is short compared with most of ethnographic digging sticks
recorded, but it’s not rare. Different examples of short (less than 30 cm length) digging sticks
can be found in ethnography [58,60–61] as well as in archaeology [25,62]. Besides, the Ara-
nbaltza point displays cutting marks at the opposite end of the tip, showing the possibility of
having been shortened. For this reason it can’t be discarded the possibility that the original
length of this point was longer. Other wooden tools from Middle Paleolithic sites have been
also interpreted as wooden sticks. A pointed wooden pseudomorph from Abric Romanı
´’s level
J (ca. 50 kyr) has been interpreted, based on its morphology, as a massive digging stick, or
more probably as the end of a post or a stake, but no direct use-wear evidence is available [17].
Also, the tool fragments from Poggetti Vecchi have been interpreted from its morphology as
digging sticks [14].
Digging soil can be done for different reasons, for finding edible USOs (Underground Stor-
age Organs- tubers and roots) or animals; for extracting lithic raw materials or for making neg-
ative structures (i.e. pot holes or sepultures). In the archaeological record there is almost no
empirical evidence to support this kind of activities, which have been inferred through indirect
evidence. For example, the consumption of USOs by Neanderthals in Europe has been sug-
gested through direct analysis of dental calculus or fecal remains [63–65]. In the surroundings
of Aranbaltza different edible USOs would have been available given their known distributions
in different climatic scenarios [66]. Furthermore, the pollen analysis from Unit 4 revealed the
presence of cattails (Typha), indicating that plants with edible USOs could be found close to
the site. On the other hand, there is little evidence of underground animal gathering through
digging [67], but the presence of hare and rabbit has been documented in contemporary sites
Middle Palaeolithic wooden digging stick from Aranbaltza III
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like Axlor, Lezetxiki, Covalejos or Atxagakoa [68–70]. Also, shellfish gathering has been pro-
posed as a possible function for digging sticks. Although no direct evidence is available at the
site, in the nearby site of El Cuco, dated back ca. 44 ka BP [36] unquestionable evidence of lim-
pet consume has been recorded. Regarding raw material collection, the presence of flint from
primary sources has been attested in different levels of Aranbaltza III, and also in the Middle
Palaeolithic levels from Aranbaltza I. Flysch flint appears in different contexts close to the site
(<500 m). Interestingly, the best quality flint is nowadays present in a muddy olitostrome [71]
and some digging was probably needed to extract the nodules. Finally, Neanderthals are
known to have dug simple structures into the soil to build shelters [45] or to bury corpses [72].
In Aranbaltza I, remnants of stone structures (pavements, fireplaces and windshields) built by
Neanderthals have been found in association with abundant lithic remains probably contem-
poraneous with Unit 1 from Aranbaltza III. For this kind of construction to take place a certain
degree of digging must have been needed.
Conclusion
A well-preserved Middle Palaeolithic wooden tool has been recovered in southern Europe. The
analysis of the technological features and the use-wear of the artefact have revealed that it was
shaped from a yew trunk through a complex operational sequence to create a pointed tool that
was used as a digging stick. This one of the first evidence of such a tool in a Late European Middle
Palaeolithic context and its possible functions have been explored, including its use in the pro-
curement of USOs, burrowing animals, and/or lithic raw materials; or to dig features in the soil.
This is one of the rarer examples in which we are able to delve directly into Palaeolithic wooden
technology thanks to the particular and exceptional preservation conditions of this piece. This
artefact highlights the relevance that wooden technology must have had for Neanderthal commu-
nities, a relevance that has been perceived almost always through indirect sources of evidence.
Supporting information
S1 File. Stratigraphy and sedimentology of Aranbaltza III sequence.
(PDF)
S2 File. Lithic assemblages from Aranbaltza III sequence.
(PDF)
S3 File. OSL dating.
(PDF)
S4 File. Virtual reconstruction of the pointed tool (right) obtained from 3D model of the
piece at its current condition (left).
(TIFF)
S5 File. 3D reconstruction of the wooden pointed tool (.obj file with texture).
(ZIP)
S6 File. 3D reconstruction of the other wooden tool from U4 (.obj file with texture).
(ZIP)
Acknowledgments
The archeological work at Aranbaltza site is funded by the Diputacio
´n Foral de Bizkaia (2013–
2017) and the Basque Government (2014, 2015). The project was also helped by the Barrika
Town Council and Harpea Kultur Elkartea. The site of Aranbaltza is located in the private
Middle Palaeolithic wooden digging stick from Aranbaltza III
PLOS ONE | https://doi.org/10.1371/journal.pone.0195044 March 28, 2018 11 / 15

property of the “Club Hı
´pico Barrika” and during the fieldwork we always had the disinter-
ested help of the owner, Damia
´n Libano. The Microscopy Laboratory technicians Bele
´n
Notario Collado and Pablo Pardo (CENIEH) helped through the CT scan and the microscopic
analysis of the piece. Asier Go
´mez-Olivencia (IKERBASQUE) helped with the CT scan image
processing. Pablo Aparicio made the virtual restoration of the piece. The restoration techni-
cian, Pilar Fernandez (CENIEH) preserved the piece in its current condition. Patricia Bello
(CENIEH) was helpful providing tuber processing references. We want to thank also Ara-
nbaltza fieldwork volunteers, especially Daniel Ruiz and Fazia Bouchoud who found the point,
and the Arkeologi Museoa of Bilbao.
Author Contributions
Conceptualization: Joseba Rios-Garaizar, Oriol Lo
´pez-Bulto
´, Illuminada Ortega-Cordellat.
Formal analysis: Joseba Rios-Garaizar, Oriol Lo
´pez-Bulto
´, Eneko Iriarte, Carlos Pe
´rez-Gar-
rido, Raquel Pique
´, Arantza Aranburu, Marı
´a Jose
´Iriarte-Chiapusso.
Funding acquisition: Joseba Rios-Garaizar, Illuminada Ortega-Cordellat, Diego Garate, Iñaki
Libano.
Investigation: Joseba Rios-Garaizar, Oriol Lo
´pez-Bulto
´, Eneko Iriarte, Carlos Pe
´rez-Garrido,
Illuminada Ortega-Cordellat, Laurence Bourguignon.
Methodology: Joseba Rios-Garaizar, Oriol Lo
´pez-Bulto
´, Eneko Iriarte, Carlos Pe
´rez-Garrido,
Raquel Pique
´, Arantza Aranburu, Marı
´a Jose
´Iriarte-Chiapusso.
Project administration: Joseba Rios-Garaizar, Diego Garate.
Supervision: Joseba Rios-Garaizar, Iñaki Libano.
Writing – original draft: Joseba Rios-Garaizar, Oriol Lo
´pez-Bulto
´, Eneko Iriarte, Carlos
Pe
´rez-Garrido, Raquel Pique
´, Arantza Aranburu, Marı
´a Jose
´Iriarte-Chiapusso, Illuminada
Ortega-Cordellat, Laurence Bourguignon, Diego Garate, Iñaki Libano.
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