- Email: [email protected]
Breakage patterns in Sima de los Huesos (Atapuerca, Spain) hominin sample
Accepted Manuscript Breakage patterns in Sima de los Huesos (Atapuerca, Spain) hominin sample Nohemi Sala, Juan Luis Arsuaga, Ignacio Martínez, Ana Gracia-Téllez PII:
S0305-4403(15)00005-9
DOI:
10.1016/j.jas.2015.01.002
Reference:
YJASC 4307
To appear in:
Journal of Archaeological Science
Received Date: 18 November 2014 Revised Date:
5 January 2015
Accepted Date: 7 January 2015
Please cite this article as: Sala, N., Arsuaga, J.L., Martínez, I., Gracia-Téllez, A., Breakage patterns in Sima de los Huesos (Atapuerca, Spain) hominin sample, Journal of Archaeological Science (2015), doi: 10.1016/j.jas.2015.01.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
Breakage patterns in Sima de los Huesos (Atapuerca, Spain) hominin sample
2
Nohemi Salaa,b*, Juan Luis Arsuagaa,b, Ignacio Martíneza,c, Ana Gracia-Télleza,d
3
a
4
Spain.
5
b
6
c
7
d
8
* Corresponding author:
9
Nohemi Sala
Departamento de Paleontología. Universidad Complutense de Madrid, Spain.
RI PT
Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos. C/ Monforte de Lemos, 5. 28029 Madrid,
Área de Antropología Física. Departamento de Ciencias de la Vida. Universidad de Alcalá. Madrid, Spain.
M AN U
SC
Área de Paleontología. Departamento de Geografía y Geología. Universidad de Alcalá. Madrid, Spain.
Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos.
11
C/ Monforte de Lemos, 5. 28029, Madrid, Spain.
12
[email protected]
13
Tel: +34 91 822 28 51; Fax: +34 91 822 28 55
EP AC C
14
TE D
10
1
ACCEPTED MANUSCRIPT Abstract
16
Fracture pattern analysis implement the taphonomic information obtained and it help
17
understanding the largest accumulation of human remains from the Middle Pleistocene
18
known, the Sima de los Huesos (SH) sample. The SH hominin long bones exhibit a
19
fracture pattern characterized especially by the dominance of transverse fractures of the
20
long axis, complete circumferences and fracture edges with right angles and jagged
21
surfaces. These properties are expected for post-depositional fractures and are
22
compatible with collective burial assemblages. The very small proportion of fractures
23
typical of biostratinomic stage could be due to a blunt force trauma produced by a free-
24
fall down the vertical 13 m shaft that constitutes the access to the SH chamber.
25
Keywords: Taphonomy, bone breakage, Middle Pleistocene.
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ACCEPTED MANUSCRIPT 1. Introduction
28
One of the key factors necessary for interpreting the origin of an accumulation of
29
skeletal remains and developing a taphonomic history is recognizing the processes
30
involved in fracturing. Bone is a two-phase material, and consists of an organic portion
31
(collagen) and another inorganic portion (a calcium phosphate mineral called
32
hydroxyapatite). The mineral phase provides rigidity and hardness while collagen
33
provides toughness, resiliency and elasticity to bones (Lyman, 1994 and references
34
therein). The bones differ in properties with regard to fracturing if they are conserved or
35
do not have collagen (Amprino, 1958, Johnson, 1985), i.e., if they behave as rigid or
36
elastic bodies, since a wet bone has more energy when it absorbs stress than a dry bone
37
(Evans, 1957). These features allow us, in principle, to establish criteria for recognizing
38
the state of the bone at the time of fracturing: fresh (or green) bone (that preserves
39
organic fractions), or dry bone (without collagen).
40
By taking these properties into account, we should be able to interpret two important
41
factors regarding bone breakage: the condition of the bone when the fracture occurred,
42
and the taphonomic agent responsible for the fractured bones (hominins, feeding
43
carnivores, weathering, trampling or geological agents). It is not always possible to
44
determine the agent responsible for fracturing the bones unless the mark associated is
45
preserved, but at least the fracture analysis allows us to determine if the bones have
46
been fractured in a dry or wet state. Wet state fractures occur while the bone contains
47
muscles, periosteum, skin and other soft tissues and have plastic properties. So fresh
48
fracturing can be ante- and perimortem (around death). Perimortem fractures, in
49
contrast to antemortem injuries, exhibit no evidence of healing (Ortner, 2008, Ubelaker
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3
ACCEPTED MANUSCRIPT and Adams, 1995). Postmortem fractures take place when fracturing occurs on
51
defleshed bones, and contain no muscles or skin and undoubtedly the process occurs
52
after the individual's death.
53
Force must be applied to a bone to break it. There are two types of forces that can be
54
applied to a bone: a static loading force that involves the application of constant
55
pressure (i.e., sedimentary pressure on buried bones) or a dynamic loading force that
56
involves focused sudden impact (i.e., percussion by stone tools).
57
Hominin skeletal remains are usually found broken in Pleistocene archaeological sites.
58
How and when the bones were broken is one of the main taphonomical questions that
59
require an answer. The bone fracturation pattern in archaeological contexts differs
60
depending on the origin of the accumulation and is usually examined based on different
61
marks on the bone surface. In anthropic contexts (i.e., cannibalism) the intentional
62
fracturation is interpreted when cutmarks, peeling and percussion marks are found (this
63
is the case for the Gran Dolina TD-6 hominin remains; (Fernández-Jalvo et al., 1996,
64
1999, Saladié et al., 2011, 2012) and other fracture properties, such as V-shaped and
65
bevelled break patterns at an oblique angle as in the case of Moula-Guercy
66
Neanderthals, (Defleur et al., 1993, 1999). Also in El Sidrón, Neanderthals’ conchoidal
67
percussion scars and cutmarks are presumably related to a hominin breakage origin
68
(Rosas et al., 2006).
69
In intentional or natural hominin burial sites, fracture patterns are less frequent and
70
typically bone breakage is interpreted as caused by sediment pressure or block falls.
71
Nevertheless, there is a lack of specific research addressing fracture patterns in
72
Pleistocene hominin burials.
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ACCEPTED MANUSCRIPT Villa and Mahieu (1991) establish a complete methodological framework for the study
74
of fractures in hominin long bones and they compare the frequency of the attributes
75
among three prehistoric assemblages of known accumulation origin: Late Neolithic
76
collective burial (Sarrians site), ancient anthropic (cannibalism) fracturation
77
(Fontbrégoua Early and Middle Neolithic site) and the excavation fractures sample
78
(Bezouce site).
79
Literature from other archaeological contexts without hominin remains is extensive and
80
facilitates understanding of the origin of the faunal bones accumulation (Alcántara-
81
García et al., 2006, Binford, 1981, Brain, 1981, Church and Lyman, 2003, Haglund et
82
al., 1988, Haynes, 1983, Karr and Outram, 2012, Klein and Cruz-Uribe, 1984, Morlan,
83
1984, Myers et al., 1980, Outram, 2001, 2002, Outram et al., 2005, Pérez Ripoll, 1992,
84
Pickering et al., 2005, Todd and Rapson, 1988), among others. Forensic works are
85
abundant and of interest in order to interpret the time of the breakage: i.e. antemortem,
86
perimortem or postmortem stages (Evans, 1952, 1957, Fleming-Farrell et al., 2013,
87
Petaros et al., 2013, Quatrehomme and Iscan, 1997, Wheatley, 2008), among others.
88
Obviously, in Pleistocene contexts where no soft tissue is preserved, the identification
89
of the perimortem period is far less accurate than in forensic cases.
90
Previous research deals with fracture patterns in the Sima de los Huesos (SH) hominin
91
sample (Andrews and Fernández-Jalvo, 1997, Arsuaga et al., 1990). Those works
92
concur with the fact that in the SH sample most of the bones show fractures. The first
93
taphonomical work suggests that the long bones display post-fossilization breakage
94
(Arsuaga et al., 1990). The latter work (Andrews and Fernández-Jalvo, 1997) suggest
95
two types of breakage were equally represented in the SH assemblage, green-bone
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ACCEPTED MANUSCRIPT breakage, and dry-stick breakage occurring sometime after deposition but not recently.
97
Andrews and Fernández Jalvo (1997) also concluded that the breakage of the human
98
bones provides no evidence that they entered the cave by being dropped down the 13 m
99
vertical shaft. New taphonomic studies in hominin sample from SH state the evidence
100
of carnivore activity is of very low frequency and indicates only sporadic carnivore
101
activity at the site (Sala et al., 2014b). There is no evidence of cutmarks or any other
102
anthropic activity in the bones of the SH collection (Andrews and Fernández-Jalvo,
103
1997, Arsuaga et al., 1997, Sala et al., 2014b).
104
Therefore, there has never been a firm consensus regarding the causes of fracturation in
105
the human bones found in SH. This new study on the taphonomy of the SH sample
106
attempts to provide new data to contrast the different interpretations on this matter. The
107
objective of the present work is to describe and to quantify the fracturation patterns
108
observed in the SH.
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2. Material and Methods
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2.1 Sima de los Huesos Site
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The Sima de los Huesos (SH) site (Atapuerca, Burgos, Spain) is a small chamber at the
113
foot of a shaft located deep inside an underground karst system (Arsuaga et al., 1997).
114
Inside this chamber, twelve lithostratigraphic units (LU) were defined, but only two of
115
them (LU-6 and LU-7) are fossiliferous stratigraphic levels (Fig. 1) (Aranburu et al.,
116
Submitted). LU-6 consists of plastic red clays with a high density of hominin and
117
carnivore fossils. The red clay matrix is pure, devoid of extraclasts, and indicates low
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ACCEPTED MANUSCRIPT energy accumulation (decantation), which is compelling evidence that the fossils were
119
not subjected to long-distance transport (Aranburu et al., submitted). To date, over
120
6,700 human fossils, belonging to at least 28 individuals are represented in this
121
stratigraphic level (LU-6) (Arsuaga et al., 2014). A small portion (< 7% of the current
122
collection) of the hominin fossils from LU-6 was moved from the “in situ” levels to the
123
uppermost part of the site and disturbed and trampled by cavers before the formal
124
excavation period (Arsuaga et al., 1997).
125
Together with the hominin bones, thousands of remains of Ursus deningeri (MNI =
126
200) and other carnivores as well as microfaunal remains have been recovered (Arsuaga
127
et al., 2014, Cuenca-Bescós et al., 1997, Cuenca-Bescós and García, 2007, García et al.,
128
1997, García and Arsuaga, 2011). Hominin bones are present in the red clay level (LU-
129
6), but carnivores (especially bears) are present in both stratigraphic levels (LU-6 and
130
LU-7) (Aranburu et al., Submitted, Arsuaga et al., 2014). As yet, no ungulate remains
131
have been found at the site. Using a variety of techniques, the hominin-bearing layer
132
could be assigned to a period around 430 thousand years ago (Arsuaga et al., 2014).
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2.2 The SH Fossil Sample
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The human sample from SH is a large collection composed of more than 6,740 bone
136
fragments of all skeletal portions. Some of the remains fit together to form complete
137
bones. In this paper, we provide fracturation features of the hominin long and flat
138
postcranial bones: femur (Number of Identified Specimens NISP=77), tibia (NISP=33),
139
fibula (NISP=111), metatarsal (NISP=119), clavicle (NISP=42), humerus (NISP=87),
140
radius (NISP=62), ulna (NISP=58), metacarpal (NISP=89), innominate (NISP=148),
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ACCEPTED MANUSCRIPT ribs (NISP=197), vertebra (NISP=203) and scapula (NISP=67) of the SH assemblage.
142
The phalanges (NISP=531), carpal and tarsal bones (NISP: 143) were quantified in
143
relation to the presence/absence of fractures because of their small size and high
144
density, which provide less information about fracturation processes. Dental remains
145
and bone fragments smaller than 2 cm were excluded. Cranial bones require a specific
146
study due to the complexity and different methodology necessary to conduct the
147
analysis. An inventory of human remains studied is included as supplementary material
148
(SI).
149
2.3 Methodological procedure
150
The SH bones are embedded in a highly humid, plastic and sticky clay sediment. This
151
makes them behave in a peculiar way that sometimes makes it difficult to differentiate
152
ancient and modern fractures. The usual criteria used to differentiate taphonomical
153
fractures from modern fractures, such as if their broken edges appear to be clean under
154
magnification, different coloration in fracture surface or if they are sharp and free of
155
matrix (Russell, 1987, Ubelaker and Adams, 1995), are not always diagnostic in this
156
field. This is because the clay moisture penetrates the bone, giving it a homogeneous
157
appearance. Furthermore, small changes in burial conditions, e.g., the excavation
158
process, sometimes produce cracks that are held together while the bone remains are
159
still buried, but are separated when the clay is removed. Due to the difficulty involved
160
in identifying this type of fragmentation in SH, the behavior of the fossils during the
161
2007 - 2014 excavation campaigns has been monitored. To that end, the characteristics
162
of the bones at the site have been noted, e.g., if they were complete, broken, cracked or
163
otherwise and if fractures occurred during excavation. Subsequently and before cleaning
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ACCEPTED MANUSCRIPT them, we took detailed pictures and the remains were described. This has allowed us to
165
recognize the fracture properties in SH, thus helping us to interpret the rest of the
166
analysed collection. Therefore, in this work, the distinction was made between fractures
167
and fissures. Fractures correspond to bone breakage caused by any agent - e.g.,
168
carnivore biting, sediment pressure, etc. - while fissures are small cracks produced when
169
the burial conditions are changed (during the excavation of the fossil) without a
170
fracturing agent. Consequently, some bones from SH, despite being composed of
171
numerous fragments, actually belong to a single excavation unit (a single label) whose
172
fragments are separated by fissures during the excavation processes. In this study we
173
analysed only fractures, considering the excavation unit as bone fragment.
174
The fractures on the human remains were analysed and classified according to Villa and
175
Mahieu (1991) and are described as follows (Fig. 2).
176
Fracture outline: orientation of the fracture with respect to the long axis of the bone:
177
longitudinal, transverse or oblique/curved (Gifford-González, 1989, Haynes, 1983, Villa
178
and Mahieu, 1991).
179
Fracture angle: This is the angle formed by the fracture surface and the bone cortical
180
surface (Villa and Mahieu, 1991). This angle (α in Fig. 2) can be right (around 90º),
181
oblique for fractures that have more than 105º or less than 85º (Alcántara-García et al.,
182
2006) or mixed (when the bone exhibit both types of fracture angles).
183
Fracture edge: This feature describes the texture of the fracture’s surfaces. We consider
184
two attributes, smooth or jagged, following the criteria of Villa and Mahieu (1991).
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ACCEPTED MANUSCRIPT Shaft Circumference: When a bone is fractured along the shaft portion, it may comprise
186
the entire circumference or not. To quantify it, Villa and Mahieu (1991) completed a
187
numerical index, similar to those used by Bunn (Bunn, 1982, 1983) which are: 1) Less
188
than half of the circumference; 2) more than half of the circumference; 3) complete
189
circumference in at least, a portion of the bone diaphysis.
190
Shaft fragment: This feature attempts to quantify the portion of diaphysis that is
191
preserved. We have considered four numerical indexes following Bunn (1982, 1983)
192
and Villa and Mahieu (1991): 1) Less than 1/4 of the total diaphysis; 2) between 1/4 -
193
1/2 of the total diaphysis; 3) between 1/2 to 3/4 of the diaphysis; 4) increased from 3/4
194
of the diaphysis.
195
In order to compare the fracture properties of SH with other comparative samples, we
196
performed a Multiple Correspondence Analysis (MCA) using the STATISTICA 8.0
197
(StatSoft, 2007) software. The samples included in the MCA analysis are divided into
198
four groups. The first group is composed of green bone breakage assemblages of
199
hominin long bones broken for marrow extraction (cannibalism scenario): Fontbrégoua
200
(data from Villa and Mahieu, 1991) and the assemblage of the Bronze Age level
201
(MIR4A) at El Mirador Cave (Atapuerca, Burgos) (Cáceres et al., 2007). The human
202
remains of the Mirador Cave site were boiled before buried and, therefore, the cooking
203
process could modify to some extent the characteristics of the fractures, so the data must
204
be taken with caution. The second group consists of two collective burials (hominin
205
assemblages) with two types of fracturing agents: i) breakage by sediment pressure:
206
Sarrians (Villa and Mahieu, 1991) and ii) breakage by archaeological works: Bezouce
207
(Villa and Mahieu, 1991). The third group is composed of two faunal assemblages from
208
Pleistocene carnivore dens: Cueva del Camino (Pinilla del Valle, Madrid, Spain) and 10
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ACCEPTED MANUSCRIPT Cueva de la Zarzamora (Segovia, Spain) (Arsuaga et al., 2012, Sala et al., 2012),
210
assuming that the main fracturing occurred during the biostratinomic stage (green bone
211
breakage caused by carnivore activity). The last group consists of bears’ (Ursus
212
deningeri) long bones from the two fossiliferous layers (LU-6 and LU-7) of SH, that
213
clearly show a post-depositional fractures by sediment pressure (Sala, 2012). For
214
comparative purposes only, long bones were taken into account since they constituted a
215
good sample for our purposes due to their morphology and their behaviour.
216
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3. Results
219
3.1 Long bones sample
220
The study of fracture patterns in the human fossil sample of SH reveals that 564
221
(82.8%) long bones display fractures (Table 1 and Fig. 3). Of the complete long bones
222
(117), 80 correspond to unfused immature epiphyses, so if we did not take these
223
remains into account, the percentage of broken diaphyses would be even higher
224
(94.6%). Therefore, the SH hominin sample has been subjected to fracturing processes.
225
The main characteristics of the fractures in hominin long bones are described as follows.
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Regarding the fracture outline of broken long bones, almost 80% (NISP=466) of the
228
sample is characterized by having transversal fractures to the long axis of the bone.
229
When analysing the sample by bone type, we can observe that thinner diaphysis bones
230
(ulna and fibula) surpass 90% of the sample with transverse fractures. Large long bones
231
such as the femur, tibia, humerus and radius show transversal fractures in 80% of cases. 11
ACCEPTED MANUSCRIPT Clavicles are long bones with a higher incidence of oblique outlines in the fractures
233
(Table 1 and Fig. 3).
234
Almost 90% of the fracture planes are right angled. The clavicles reach 100%, and more
235
than 90% of the fibula, radius and ulna have right angles. Bevelled angles are rare in the
236
SH hominin sample and only appear in femur and metatarsal bones. Metapodials exhibit
237
the highest frequencies of mixed angles, followed by the femur and the humerus (Table
238
1 and Fig. 3).
239
Regarding the texture of the fracture surface most of the sample (96.0%) has jagged
240
surfaces on the broken edges (Table 1 and Fig. 3). Mixed texture is also present,
241
especially in metacarpal, humerus and femur fracture surfaces.
242
Another attribute analysed was the completeness of the long bone diaphyses, in terms of
243
circumference (shaft circumference) and size of the fragment (shaft fragment).
244
Considering the whole sample, we can observe that circumferences are complete in
245
more than 90% of the hominin long bones (Table 1, Figs. 3 and 4). This percentage
246
varies, according to bone type: between 72% (tibia) and 98% (radius) of the bones
247
analysed.
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Although fragments clearly dominate close to one quarter of the shaft, this feature is
250
variable depending on the type of bone. In general, smaller fragments dominate (<1/4 of
251
the total length) followed by diaphyseal halves, then thirds and so on to full lengths.
252
This trend is observed in all kinds of bones except for the femur, metatarsal and
253
metacarpal diaphyses (Table 1, Figs. 3 and 4). 12
ACCEPTED MANUSCRIPT
S0305-4403(15)00005-9
DOI:
10.1016/j.jas.2015.01.002
Reference:
YJASC 4307
To appear in:
Journal of Archaeological Science
Received Date: 18 November 2014 Revised Date:
5 January 2015
Accepted Date: 7 January 2015
Please cite this article as: Sala, N., Arsuaga, J.L., Martínez, I., Gracia-Téllez, A., Breakage patterns in Sima de los Huesos (Atapuerca, Spain) hominin sample, Journal of Archaeological Science (2015), doi: 10.1016/j.jas.2015.01.002. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
Breakage patterns in Sima de los Huesos (Atapuerca, Spain) hominin sample
2
Nohemi Salaa,b*, Juan Luis Arsuagaa,b, Ignacio Martíneza,c, Ana Gracia-Télleza,d
3
a
4
Spain.
5
b
6
c
7
d
8
* Corresponding author:
9
Nohemi Sala
Departamento de Paleontología. Universidad Complutense de Madrid, Spain.
RI PT
Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos. C/ Monforte de Lemos, 5. 28029 Madrid,
Área de Antropología Física. Departamento de Ciencias de la Vida. Universidad de Alcalá. Madrid, Spain.
M AN U
SC
Área de Paleontología. Departamento de Geografía y Geología. Universidad de Alcalá. Madrid, Spain.
Centro Mixto UCM-ISCIII de Evolución y Comportamiento Humanos.
11
C/ Monforte de Lemos, 5. 28029, Madrid, Spain.
12
[email protected]
13
Tel: +34 91 822 28 51; Fax: +34 91 822 28 55
EP AC C
14
TE D
10
1
ACCEPTED MANUSCRIPT Abstract
16
Fracture pattern analysis implement the taphonomic information obtained and it help
17
understanding the largest accumulation of human remains from the Middle Pleistocene
18
known, the Sima de los Huesos (SH) sample. The SH hominin long bones exhibit a
19
fracture pattern characterized especially by the dominance of transverse fractures of the
20
long axis, complete circumferences and fracture edges with right angles and jagged
21
surfaces. These properties are expected for post-depositional fractures and are
22
compatible with collective burial assemblages. The very small proportion of fractures
23
typical of biostratinomic stage could be due to a blunt force trauma produced by a free-
24
fall down the vertical 13 m shaft that constitutes the access to the SH chamber.
25
Keywords: Taphonomy, bone breakage, Middle Pleistocene.
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15
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2
ACCEPTED MANUSCRIPT 1. Introduction
28
One of the key factors necessary for interpreting the origin of an accumulation of
29
skeletal remains and developing a taphonomic history is recognizing the processes
30
involved in fracturing. Bone is a two-phase material, and consists of an organic portion
31
(collagen) and another inorganic portion (a calcium phosphate mineral called
32
hydroxyapatite). The mineral phase provides rigidity and hardness while collagen
33
provides toughness, resiliency and elasticity to bones (Lyman, 1994 and references
34
therein). The bones differ in properties with regard to fracturing if they are conserved or
35
do not have collagen (Amprino, 1958, Johnson, 1985), i.e., if they behave as rigid or
36
elastic bodies, since a wet bone has more energy when it absorbs stress than a dry bone
37
(Evans, 1957). These features allow us, in principle, to establish criteria for recognizing
38
the state of the bone at the time of fracturing: fresh (or green) bone (that preserves
39
organic fractions), or dry bone (without collagen).
40
By taking these properties into account, we should be able to interpret two important
41
factors regarding bone breakage: the condition of the bone when the fracture occurred,
42
and the taphonomic agent responsible for the fractured bones (hominins, feeding
43
carnivores, weathering, trampling or geological agents). It is not always possible to
44
determine the agent responsible for fracturing the bones unless the mark associated is
45
preserved, but at least the fracture analysis allows us to determine if the bones have
46
been fractured in a dry or wet state. Wet state fractures occur while the bone contains
47
muscles, periosteum, skin and other soft tissues and have plastic properties. So fresh
48
fracturing can be ante- and perimortem (around death). Perimortem fractures, in
49
contrast to antemortem injuries, exhibit no evidence of healing (Ortner, 2008, Ubelaker
AC C
EP
TE D
M AN U
SC
RI PT
27
3
ACCEPTED MANUSCRIPT and Adams, 1995). Postmortem fractures take place when fracturing occurs on
51
defleshed bones, and contain no muscles or skin and undoubtedly the process occurs
52
after the individual's death.
53
Force must be applied to a bone to break it. There are two types of forces that can be
54
applied to a bone: a static loading force that involves the application of constant
55
pressure (i.e., sedimentary pressure on buried bones) or a dynamic loading force that
56
involves focused sudden impact (i.e., percussion by stone tools).
57
Hominin skeletal remains are usually found broken in Pleistocene archaeological sites.
58
How and when the bones were broken is one of the main taphonomical questions that
59
require an answer. The bone fracturation pattern in archaeological contexts differs
60
depending on the origin of the accumulation and is usually examined based on different
61
marks on the bone surface. In anthropic contexts (i.e., cannibalism) the intentional
62
fracturation is interpreted when cutmarks, peeling and percussion marks are found (this
63
is the case for the Gran Dolina TD-6 hominin remains; (Fernández-Jalvo et al., 1996,
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1999, Saladié et al., 2011, 2012) and other fracture properties, such as V-shaped and
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bevelled break patterns at an oblique angle as in the case of Moula-Guercy
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Neanderthals, (Defleur et al., 1993, 1999). Also in El Sidrón, Neanderthals’ conchoidal
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percussion scars and cutmarks are presumably related to a hominin breakage origin
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(Rosas et al., 2006).
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In intentional or natural hominin burial sites, fracture patterns are less frequent and
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typically bone breakage is interpreted as caused by sediment pressure or block falls.
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Nevertheless, there is a lack of specific research addressing fracture patterns in
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Pleistocene hominin burials.
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of fractures in hominin long bones and they compare the frequency of the attributes
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among three prehistoric assemblages of known accumulation origin: Late Neolithic
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collective burial (Sarrians site), ancient anthropic (cannibalism) fracturation
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(Fontbrégoua Early and Middle Neolithic site) and the excavation fractures sample
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(Bezouce site).
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Literature from other archaeological contexts without hominin remains is extensive and
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facilitates understanding of the origin of the faunal bones accumulation (Alcántara-
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García et al., 2006, Binford, 1981, Brain, 1981, Church and Lyman, 2003, Haglund et
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al., 1988, Haynes, 1983, Karr and Outram, 2012, Klein and Cruz-Uribe, 1984, Morlan,
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1984, Myers et al., 1980, Outram, 2001, 2002, Outram et al., 2005, Pérez Ripoll, 1992,
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Pickering et al., 2005, Todd and Rapson, 1988), among others. Forensic works are
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abundant and of interest in order to interpret the time of the breakage: i.e. antemortem,
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perimortem or postmortem stages (Evans, 1952, 1957, Fleming-Farrell et al., 2013,
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Petaros et al., 2013, Quatrehomme and Iscan, 1997, Wheatley, 2008), among others.
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Obviously, in Pleistocene contexts where no soft tissue is preserved, the identification
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of the perimortem period is far less accurate than in forensic cases.
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Previous research deals with fracture patterns in the Sima de los Huesos (SH) hominin
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sample (Andrews and Fernández-Jalvo, 1997, Arsuaga et al., 1990). Those works
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concur with the fact that in the SH sample most of the bones show fractures. The first
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taphonomical work suggests that the long bones display post-fossilization breakage
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(Arsuaga et al., 1990). The latter work (Andrews and Fernández-Jalvo, 1997) suggest
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two types of breakage were equally represented in the SH assemblage, green-bone
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ACCEPTED MANUSCRIPT breakage, and dry-stick breakage occurring sometime after deposition but not recently.
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Andrews and Fernández Jalvo (1997) also concluded that the breakage of the human
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bones provides no evidence that they entered the cave by being dropped down the 13 m
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vertical shaft. New taphonomic studies in hominin sample from SH state the evidence
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of carnivore activity is of very low frequency and indicates only sporadic carnivore
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activity at the site (Sala et al., 2014b). There is no evidence of cutmarks or any other
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anthropic activity in the bones of the SH collection (Andrews and Fernández-Jalvo,
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1997, Arsuaga et al., 1997, Sala et al., 2014b).
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Therefore, there has never been a firm consensus regarding the causes of fracturation in
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the human bones found in SH. This new study on the taphonomy of the SH sample
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attempts to provide new data to contrast the different interpretations on this matter. The
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objective of the present work is to describe and to quantify the fracturation patterns
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observed in the SH.
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2. Material and Methods
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2.1 Sima de los Huesos Site
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The Sima de los Huesos (SH) site (Atapuerca, Burgos, Spain) is a small chamber at the
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foot of a shaft located deep inside an underground karst system (Arsuaga et al., 1997).
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Inside this chamber, twelve lithostratigraphic units (LU) were defined, but only two of
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them (LU-6 and LU-7) are fossiliferous stratigraphic levels (Fig. 1) (Aranburu et al.,
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Submitted). LU-6 consists of plastic red clays with a high density of hominin and
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carnivore fossils. The red clay matrix is pure, devoid of extraclasts, and indicates low
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ACCEPTED MANUSCRIPT energy accumulation (decantation), which is compelling evidence that the fossils were
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not subjected to long-distance transport (Aranburu et al., submitted). To date, over
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6,700 human fossils, belonging to at least 28 individuals are represented in this
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stratigraphic level (LU-6) (Arsuaga et al., 2014). A small portion (< 7% of the current
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collection) of the hominin fossils from LU-6 was moved from the “in situ” levels to the
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uppermost part of the site and disturbed and trampled by cavers before the formal
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excavation period (Arsuaga et al., 1997).
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Together with the hominin bones, thousands of remains of Ursus deningeri (MNI =
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200) and other carnivores as well as microfaunal remains have been recovered (Arsuaga
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et al., 2014, Cuenca-Bescós et al., 1997, Cuenca-Bescós and García, 2007, García et al.,
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1997, García and Arsuaga, 2011). Hominin bones are present in the red clay level (LU-
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6), but carnivores (especially bears) are present in both stratigraphic levels (LU-6 and
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LU-7) (Aranburu et al., Submitted, Arsuaga et al., 2014). As yet, no ungulate remains
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have been found at the site. Using a variety of techniques, the hominin-bearing layer
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could be assigned to a period around 430 thousand years ago (Arsuaga et al., 2014).
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2.2 The SH Fossil Sample
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The human sample from SH is a large collection composed of more than 6,740 bone
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fragments of all skeletal portions. Some of the remains fit together to form complete
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bones. In this paper, we provide fracturation features of the hominin long and flat
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postcranial bones: femur (Number of Identified Specimens NISP=77), tibia (NISP=33),
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fibula (NISP=111), metatarsal (NISP=119), clavicle (NISP=42), humerus (NISP=87),
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radius (NISP=62), ulna (NISP=58), metacarpal (NISP=89), innominate (NISP=148),
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ACCEPTED MANUSCRIPT ribs (NISP=197), vertebra (NISP=203) and scapula (NISP=67) of the SH assemblage.
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The phalanges (NISP=531), carpal and tarsal bones (NISP: 143) were quantified in
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relation to the presence/absence of fractures because of their small size and high
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density, which provide less information about fracturation processes. Dental remains
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and bone fragments smaller than 2 cm were excluded. Cranial bones require a specific
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study due to the complexity and different methodology necessary to conduct the
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analysis. An inventory of human remains studied is included as supplementary material
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(SI).
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2.3 Methodological procedure
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The SH bones are embedded in a highly humid, plastic and sticky clay sediment. This
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makes them behave in a peculiar way that sometimes makes it difficult to differentiate
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ancient and modern fractures. The usual criteria used to differentiate taphonomical
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fractures from modern fractures, such as if their broken edges appear to be clean under
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magnification, different coloration in fracture surface or if they are sharp and free of
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matrix (Russell, 1987, Ubelaker and Adams, 1995), are not always diagnostic in this
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field. This is because the clay moisture penetrates the bone, giving it a homogeneous
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appearance. Furthermore, small changes in burial conditions, e.g., the excavation
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process, sometimes produce cracks that are held together while the bone remains are
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still buried, but are separated when the clay is removed. Due to the difficulty involved
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in identifying this type of fragmentation in SH, the behavior of the fossils during the
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2007 - 2014 excavation campaigns has been monitored. To that end, the characteristics
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of the bones at the site have been noted, e.g., if they were complete, broken, cracked or
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otherwise and if fractures occurred during excavation. Subsequently and before cleaning
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ACCEPTED MANUSCRIPT them, we took detailed pictures and the remains were described. This has allowed us to
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recognize the fracture properties in SH, thus helping us to interpret the rest of the
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analysed collection. Therefore, in this work, the distinction was made between fractures
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and fissures. Fractures correspond to bone breakage caused by any agent - e.g.,
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carnivore biting, sediment pressure, etc. - while fissures are small cracks produced when
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the burial conditions are changed (during the excavation of the fossil) without a
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fracturing agent. Consequently, some bones from SH, despite being composed of
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numerous fragments, actually belong to a single excavation unit (a single label) whose
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fragments are separated by fissures during the excavation processes. In this study we
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analysed only fractures, considering the excavation unit as bone fragment.
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The fractures on the human remains were analysed and classified according to Villa and
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Mahieu (1991) and are described as follows (Fig. 2).
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Fracture outline: orientation of the fracture with respect to the long axis of the bone:
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longitudinal, transverse or oblique/curved (Gifford-González, 1989, Haynes, 1983, Villa
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and Mahieu, 1991).
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Fracture angle: This is the angle formed by the fracture surface and the bone cortical
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surface (Villa and Mahieu, 1991). This angle (α in Fig. 2) can be right (around 90º),
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oblique for fractures that have more than 105º or less than 85º (Alcántara-García et al.,
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2006) or mixed (when the bone exhibit both types of fracture angles).
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Fracture edge: This feature describes the texture of the fracture’s surfaces. We consider
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two attributes, smooth or jagged, following the criteria of Villa and Mahieu (1991).
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ACCEPTED MANUSCRIPT Shaft Circumference: When a bone is fractured along the shaft portion, it may comprise
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the entire circumference or not. To quantify it, Villa and Mahieu (1991) completed a
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numerical index, similar to those used by Bunn (Bunn, 1982, 1983) which are: 1) Less
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than half of the circumference; 2) more than half of the circumference; 3) complete
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circumference in at least, a portion of the bone diaphysis.
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Shaft fragment: This feature attempts to quantify the portion of diaphysis that is
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preserved. We have considered four numerical indexes following Bunn (1982, 1983)
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and Villa and Mahieu (1991): 1) Less than 1/4 of the total diaphysis; 2) between 1/4 -
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1/2 of the total diaphysis; 3) between 1/2 to 3/4 of the diaphysis; 4) increased from 3/4
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of the diaphysis.
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In order to compare the fracture properties of SH with other comparative samples, we
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performed a Multiple Correspondence Analysis (MCA) using the STATISTICA 8.0
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(StatSoft, 2007) software. The samples included in the MCA analysis are divided into
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four groups. The first group is composed of green bone breakage assemblages of
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hominin long bones broken for marrow extraction (cannibalism scenario): Fontbrégoua
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(data from Villa and Mahieu, 1991) and the assemblage of the Bronze Age level
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(MIR4A) at El Mirador Cave (Atapuerca, Burgos) (Cáceres et al., 2007). The human
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remains of the Mirador Cave site were boiled before buried and, therefore, the cooking
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process could modify to some extent the characteristics of the fractures, so the data must
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be taken with caution. The second group consists of two collective burials (hominin
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assemblages) with two types of fracturing agents: i) breakage by sediment pressure:
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Sarrians (Villa and Mahieu, 1991) and ii) breakage by archaeological works: Bezouce
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(Villa and Mahieu, 1991). The third group is composed of two faunal assemblages from
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Pleistocene carnivore dens: Cueva del Camino (Pinilla del Valle, Madrid, Spain) and 10
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ACCEPTED MANUSCRIPT Cueva de la Zarzamora (Segovia, Spain) (Arsuaga et al., 2012, Sala et al., 2012),
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assuming that the main fracturing occurred during the biostratinomic stage (green bone
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breakage caused by carnivore activity). The last group consists of bears’ (Ursus
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deningeri) long bones from the two fossiliferous layers (LU-6 and LU-7) of SH, that
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clearly show a post-depositional fractures by sediment pressure (Sala, 2012). For
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comparative purposes only, long bones were taken into account since they constituted a
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good sample for our purposes due to their morphology and their behaviour.
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3. Results
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3.1 Long bones sample
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The study of fracture patterns in the human fossil sample of SH reveals that 564
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(82.8%) long bones display fractures (Table 1 and Fig. 3). Of the complete long bones
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(117), 80 correspond to unfused immature epiphyses, so if we did not take these
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remains into account, the percentage of broken diaphyses would be even higher
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(94.6%). Therefore, the SH hominin sample has been subjected to fracturing processes.
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The main characteristics of the fractures in hominin long bones are described as follows.
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Regarding the fracture outline of broken long bones, almost 80% (NISP=466) of the
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sample is characterized by having transversal fractures to the long axis of the bone.
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When analysing the sample by bone type, we can observe that thinner diaphysis bones
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(ulna and fibula) surpass 90% of the sample with transverse fractures. Large long bones
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such as the femur, tibia, humerus and radius show transversal fractures in 80% of cases. 11
ACCEPTED MANUSCRIPT Clavicles are long bones with a higher incidence of oblique outlines in the fractures
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(Table 1 and Fig. 3).
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Almost 90% of the fracture planes are right angled. The clavicles reach 100%, and more
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than 90% of the fibula, radius and ulna have right angles. Bevelled angles are rare in the
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SH hominin sample and only appear in femur and metatarsal bones. Metapodials exhibit
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the highest frequencies of mixed angles, followed by the femur and the humerus (Table
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1 and Fig. 3).
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Regarding the texture of the fracture surface most of the sample (96.0%) has jagged
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surfaces on the broken edges (Table 1 and Fig. 3). Mixed texture is also present,
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especially in metacarpal, humerus and femur fracture surfaces.
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Another attribute analysed was the completeness of the long bone diaphyses, in terms of
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circumference (shaft circumference) and size of the fragment (shaft fragment).
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Considering the whole sample, we can observe that circumferences are complete in
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more than 90% of the hominin long bones (Table 1, Figs. 3 and 4). This percentage
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varies, according to bone type: between 72% (tibia) and 98% (radius) of the bones
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analysed.
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Although fragments clearly dominate close to one quarter of the shaft, this feature is
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variable depending on the type of bone. In general, smaller fragments dominate (<1/4 of
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the total length) followed by diaphyseal halves, then thirds and so on to full lengths.
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This trend is observed in all kinds of bones except for the femur, metatarsal and
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metacarpal diaphyses (Table 1, Figs. 3 and 4). 12
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