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Relationship Between Cusp Size and Occlusal Wear Pattern in Neanderthal and Homo sapiens First Maxillary Molars.

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THE ANATOMICAL RECORD 294:453–461 (2011)
Relationship Between Cusp Size
and Occlusal Wear Pattern in
Neanderthal and Homo sapiens First
Maxillary Molars
LUCA FIORENZA,1* STEFANO BENAZZI,2 BENCE VIOLA,3,4
OTTMAR KULLMER,1 AND FRIEDEMANN SCHRENK1,5
1
Department of Palaeoanthropology and Messel Research, Senckenberg Research Institute,
Senckenberganlage 25, 60325 Frankfurt am Main, Germany
2
Department of Anthropology, University of Vienna, Althanstrasse 14, 1090 Vienna,
Austria
3
Department of Human Evolution, Max-Planck Institute for Evolutionary Anthropology,
Deutscher Platz 6, 04103, Leipzig, Germany
4
Department of Evolutionary Genetics, Max-Planck Institute for Evolutionary
Anthropology, Deutscher Platz 6, 04103, Leipzig, Germany
5
Institute for Ecology, Evolution and Diversity, Johann Wolfgang Goethe University,
Siesmayerstrasse 70, 60054 Frankfurt am Main, Germany
ABSTRACT
Tooth wear studies in mammals have highlighted the relationship
between wear facets (attritional areas produced during occlusion by the
contact between opposing teeth) and physical properties of the ingested
food. However, little is known about the influence of tooth morphology on
the formation of occlusal wear facets. We analyzed the occlusal wear
patterns of first maxillary molars (M1s) in Neanderthals, early Homo
sapiens, and contemporary modern humans. We applied a virtual method
to analyze wear facets on the crown surface of three-dimensional digital
models. Absolute and relative wear facet areas are compared with cusp
area and cusp height. Although the development of wear facets partially
follows the cusp pattern, the results obtained from the between-group
comparisons do not reflect the cusp size differences characterizing these
groups. In particular, the wear facets developed along the slopes of the
most discriminate cusp between Neanderthals and Homo sapiens (hypocone) do not display any significant difference. Moreover, no correlations
have been found between cusp size and wear facet areas (with the exception of the modern sample) and between cusp height and wear facet
areas. Our results suggest that cusp size is only weakly related to the
formation of the occlusal wear facets. Other factors, such as, diet, food
processing, environmental abrasiveness, and nondietary habits are
probably more important for the development and enlargement of wear
facets, corroborating the hypotheses suggested from previous dental wear
C 2010 Wiley-Liss, Inc.
studies. Anat Rec, 294:453–461, 2011. V
Key words: Neanderthal; wear facets; cusp morphology; maxillary
first molar
Grant sponsor: EU Marie Curie Training Network; Grant
number: MRTN-CT-2005-019564 EVAN.
*Correspondence to: Luca Fiorenza, Senckenberganlage 25,
60325 Frankfurt am Main, Germany. Fax: 0049 (0) 69 7542
1558. E-mail: lfiorenza@senckenberg.de
C 2010 WILEY-LISS, INC.
V
Received 15 October 2009; Accepted 6 October 2010
DOI 10.1002/ar.21325
Published online 31 December 2010 in Wiley Online Library
(wileyonlinelibrary.com).
454
FIORENZA ET AL.
INTRODUCTION
The occlusal contacts between crests, cusps, and
basins of upper and lower dentition produce attritional
wear areas characterized by smooth, polished, and
usually well-delineated surfaces called wear facets
(Butler, 1952; Mills, 1955; Every, 1972; Kaidonis et al.,
1993; Imfeld, 1996; Hillson, 2003; Kaidonis, 2008).
Studies on numerous mammals have shown that the
type of dental wear and the relative sizes of the wear
facets can be related to their diet (Butler, 1952, 1973;
Kay, 1977; Janis, 1990). In particular, Janis (1990)
stated that the development of the occlusal wear facets
in mammals is independent from dental morphology.
Therefore, in comparing species with similar dental
morphology, dietary differences will generate different
wear patterns, whereas species with a similar diet but
with differences in dental morphology will show similar
tooth wear (Janis, 1990). No detailed tests of Janis’
hypothesis about the lack of correlation between dental
morphology and wear facet development have been
performed until now. Therefore, the influence of specific
dental morphological features on the location, development, and enlargement of wear facets is unknown.
In this study, we quantitatively test if the development of occlusal wear facets is influenced by cusp size
by analyzing and comparing tooth wear patterns of
species possessing different dental morphology. As dental
morphological differences between taxa have also been
established by detailed morphometric analysis of cusp
area (Wood and Engleman, 1988; Bailey, 2004), cusp size
is used in this study as a metric approach for describing
tooth crown morphology. We analyzed and compared
wear facet patterns of first maxillary molars (M1s) of
Neanderthals, early Homo sapiens, and contemporary
modern humans, applying the Occlusal Fingerprint Analysis method (Kullmer et al., 2009) on three-dimensional
(3D) polygonal surface models of tooth crowns.
Neanderthal Tooth Morphology
Recent comparative studies have shown that the
Neanderthal tooth morphology of first maxillary molars
is characterized by distinctive traits with a marked
expression and high frequency (Bailey, 2002, 2004, 2006;
Gómez-Robles et al., 2007; Quam et al., 2009). The
Neanderthal M1 crown commonly consists of four cusps,
characterised by a large hypocone that is never reduced
or absent, a small metacone, and other additional accessory features (Bailey, 2002, 2004, 2006; Fig. 1A).
Carabelli’s cusp is frequent and regularly well-developed
(Bailey, 2006). Distally a fifth cusp, the hypoconule, is
common (Bailey, 2006). The occlusal outline is characterized by a skewed contour and a rhomboidal shape,
resulting from a distolingual enlargement of the
hypocone and by the disposition and configuration
of internally compressed cusps (Bailey, 2002, 2004;
Gómez-Robles et al., 2007; Quam et al., 2009).
However, this morphology is not unique to Neanderthals and is also found to a lesser extent in early and
middle Pleistocene European populations (Gómez-Robles
et al., 2007; Quam et al., 2009). In contrast, contemporaneous modern humans typically show a reduced hypocone, a well-developed metacone, and a square occlusal
polygon (obtained by connecting the cusp apices of the
Fig. 1. Photo of Neanderthal (A; Le Moustier 1) and Homo sapiens
(B; Inuit FC835) first upper molars in occlusal view (par, paracone;
met, metacone; pro, protocone; hyp, hypocone).
four major cusps) associated with a square crown outline
(Bailey, 2002, 2004; Gómez-Robles et al., 2007; Quam
et al., 2009; Fig. 1B).
Although M1 morphology has been studied thoroughly,
very little is known about the occlusal wear pattern in
Neanderthal posterior dentition. Occlusal wear was
generally used for determining the age-at-death of the
Neanderthal specimens from the Krapina cave site in
Croatia (Wolpoff, 1979). Additionally, an advanced
degree of occlusal wear was associated with abrasive
food or with an abrasive environment (Trinkaus, 1983).
In recent years, scientists have focused on the study of
occlusal and buccal microwear of Neanderthal posterior
dentition using scanning electron microscope images
(Lalueza et al., 1996; Pérez-Pérez et al., 2003), confocal
microscopy, and scale-sensitive fractal analysis (El
Zaatari, 2007a, 2007b) to reconstruct their diet.
Nevertheless, none of these studies in Neanderthals
considered relationship between occlusal wear and cusp
size. If the occlusal wear pattern is independent from
cusp size, one can expect that the development of wear
facets along the slopes of the four maxillary cusps will
not be influenced by cusp morphology. Moreover, if this
hypothesis will be verified, differences in wear pattern
among Neanderthal and early Homo sapiens M1s will be
related mostly to dietary differences rather than reflecting dental morphological differences. On the contrary, a
strong relation between the development of wear facets
and cusp size will indicate that in Late Pleistocene
hominins the wear pattern is also affected by the
anatomical features of their molars, and the interpretation of any differences should be taken with care.
MATERIALS
The sample used in this study consists of fossil and
modern human M1s. The specimens listed in Table 1
include: Neanderthals (NEA, N ¼ 15), Middle Paleolithic
Homo sapiens (MPHS, N ¼ 5), Upper Paleolithic Homo
sapiens (UPHS, N ¼ 7), and contemporary modern
humans containing the Khoe-san hunter-gatherers
(MHS, N ¼ 20). The specimens were chosen based on
their degree of occlusal wear. Heavily worn teeth were
excluded because occlusal facets tend to fuse with
advanced wear, making their precise identification difficult or impossible. For this reason, we have only included
slightly-worn molars where facets are identifiable and do
WEAR FACETS ANALYSIS IN Homo sapiens M1s
455
TABLE 1. List of fossil and modern human specimens used in this study
Labels
N
Specimens
Weara
NEA
15
Middle Paleolithic
Homo sapiens
MPHS
5
Pontnewydd PN4 and PN12
Krapina 47, 48, 134, 136, 166, 167, and 171
Krapina 164
Monsempron 2 and 3
Kůlna 1
Petit Puy 2
Le Moustier 1
Qafzeh 5, 9, and 27
2
2
3
3
2
2
2
3
Upper Paleolithic
Homo sapiens
UPHS
7
Qafzeh 11 and 15
Mladec 1
2
2
20
Mladec 2
Barma Grande 3
Barma Grande 4
Sungir 2 and 3
Pataud 224
Khoe-san
3
2
3
2
3
3
Samples
Neanderthals
Modern Homo sapiens
MHS
a
Wear score system (Smith, 1984).
not coalesce in the sample. The degree of wear was
determined by evaluating the amount of cusp removal
and dentin exposure (Smith, 1984). To have a homogenous sample and to avoid a marked sample size reduction, only M1s characterized by wear stage 2 (moderate
cusp removal, with one or two pinpoint dentin exposures)
and stage 3 (full cusp removal and some dentin exposure)
were selected.
METHODS
Occlusal wear pattern analysis was carried out on 3D
digital models, which were generated through surface
scanning of M1 casts. Dental casts were produced using a
special nonreflective plaster (EverestV Rock, KaVo)
optimized for light scanning (Fiorenza et al., 2009). We
used a white-light scanning system with an x–y resolution of 55 lm (smartSCAN 3D, Breuckmann GmbH). The
scan-data was collected and aligned by means of the optoCAT software package (v. 2007, Breuckmann GmbH). The
digital postprocessing was carried out using PolyWorksV
10 (InnovMetric Software). The digital model of each
tooth was imported into the IMEdit module of
PolyworksV 10 and the cervical margin was manually
delimited using the polyline tool (Ulhaas et al., 2004,
2007). A marginal area of 0.2 mm above and below the
cervical polyline was defined and a cervical plane was
created and inserted by means of the least square, best fit
method (Ulhaas et al., 2004, 2007; Kullmer et al., 2009)
For each wear facet, a closed curve was manually
anchored on the digital model following the margin the
facet (Ulhaas et al., 2004, 2007; Kullmer et al., 2009).
Next, the digital triangles included within the facet’s
perimeter were selected and the areas in mm2 were calculated (Ulhaas et al., 2004, 2007; Kullmer et al., 2009).
Wear facets were defined on the occlusal dental surface
following the terminology of Maier and Schneck (1981),
who identified a maximum of 13 complementary pair
facets on hominoid molars (Fig. 2). Additionally, we also
identify flat worn areas on the tips of the four main cusps
(Gordon, 1984; Janis, 1990) and labeled as pro (protocone),
par (paracone), met (metacone), and hyp (hypocone).
R
R
R
The areas of the facets developed along the slopes of
the four major maxillary cusps have been grouped and
summed: protocone (facets 5, 5.1, 6, 6.1, 9, 11, 13,
and pro), paracone (facets 1, 1.1, 3, and par), metacone
(facets 2, 2.1, 4, and met), and hypocone (facets 7, 8, 10,
12, and hyp).
Considering a normal occlusion (Angle Class I), the
protocone wear facets of M1 occlude with the central
fossa of the lower M1. They are in contact with the
buccal slopes of the metaconid and entoconid and with
the lingual slopes of the protoconid, hypoconid, and
hypoconulid. The paracone wear facets develop for the
contacts with the mesiobuccal slope of the hypoconid
and with the distobuccal slope of the protoconid of the
lower M1. The metacone wear facets occlude with the
distobuccal slope of the hypoconid and with the mesiobuccal slope of the hypoconulid of the lower M1. Finally,
the development of the hypocone wear facets is because
of the contact with the distobuccal slope of the M1
entoconid and with the mesial slopes of the M2.
The total occlusal wear area was calculated as the
sum of the absolute area of each occlusal facet. The
relative cusp wear facet areas were calculated by dividing the absolute wear area of each cusp by the total
occlusal wear area.
Cusp base areas were identified on the polygonal
model (oriented in occlusal view) following the major
anatomical features that separate the cusps (Wood and
Engleman, 1988; Bailey, 2004; Fig. 3A). Then, the area
(in mm2) was calculated projecting the 3D surface of
each cusp base on the reference plane (cervical plane)
using the IMInspect module of PolyworksV 10 (Fig. 3B).
The total crown area was calculated by summing each
individual cusp base area. The relative cusp base area
was obtained by dividing each absolute cusp base area
with the total crown area.
Finally, the cusp height was calculated by measuring
the perpendicular distance between the maximum tip
point and the cervical plane (Fig. 4). An explorative data
analysis for each variable [mean and standard deviation
(SD)] and for each group was employed to investigate
cusp height, absolute and relative cusp wear area
R
456
FIORENZA ET AL.
Fig. 2. Occlusal contacts between the left first maxillary molar
and the first and second mandibular molars in the Neanderthal
specimen of Le Moustier 1. Wear facets are numbered after Maier
and Schneck (1981) and color-coded following their maxillary cusp
position: paracone (green), metacone (blue), protocone (red), and
hypocone (yellow). The division of homologous wear facets in more
parts (as facet 4) is pointed out by the letter a and b. The tip
crush areas developed along the tip of the main cusps are identified as pro (protocone), par (paracone), met (metacone), and hyp
(hypocone). In this figure, only two tip crush areas are visible on
the protocone and hypocone cusp. The arrow indicates the occlusal relationship between the protocone of the upper molar and the
central fossa of the lower during maximum intercuspation. B,
buccal; L, lingual; M, mesial; D, distal.
Fig. 3. Left M1 of Le Moustier 1: identification of cusp base areas (A) and their projection on the cervical
plane (B). Protocone (par); Paracone (Par); Metacone (met); Hypocone (hyp). The color-code follows Fig. 2.
WEAR FACETS ANALYSIS IN Homo sapiens M1s
differences among hominin groups. As the small sample
sizes prevent the assumption of a normal distribution, the
intragroup comparison of relative cusp wear areas
between molars with different wear stages, as well as the
between-group comparisons of absolute and relative cusp
areas have been carried out using nonparametric significance tests (Mann-Whitney U test). The P values obtained
have been corrected with Bonferroni adjustments.
Finally, the correlation between relative cusp areas
and relative wear facet areas and between cusp height
and relative wear facet areas has been computed using
the Spearman method. The difference in degree of wear
may affect the wear facet areas developed along the
cusp slopes. Therefore, we computed a statistical comparison of relative cusp wear areas between molars with
different wear stages. The statistical analysis has been
computed using the R software (R Development Core
Team, 2008).
457
paracone wear areas (Table 2). However, this result
could be due to the fact that most of the NEA specimens
studied here show a wear stage 2, while all MHS molars
are characterized by a wear stage 3. Consequently, to
solve this problem, we carried out one more statistical
comparison of relative cusp wear areas considering
molars with different wear stages within each group.
The reduced sample size of the MPHS sample precludes
a statistical analysis (N ¼ 2 for wear stage 2 and N ¼ 3
for wear stage 3), and therefore was not considered. The
intragroup comparisons do not show any significant
differences in all the groups examined, with the exception of the paracone wear areas within the Neanderthal
(NEA) group (Table 2).
The occlusal wear of NEA M1s is characterized by
large protocone wear areas, followed by smaller paracone, hypocone, and metacone wear areas (Tables 3 and
4). However, there is large wear pattern variability in
the NEA group, especially because of the metacone
and hypocone wear areas. Although the protocone
wear areas show the largest SD, it continues to be the
largest wear area in the NEA group. The most common
patterns found are PRO>PAR>HYP>MET (5/15) and
PRO>PAR>MET>HYP (4/15). The occlusal wear of
the Middle Paleolithic Homo sapiens (MPHS), taking
into account the small sample size, returns more
homogenous results and follows the pattern
PRO>HYP>PAR>MET (4/5).
RESULTS
The results obtained from the comparison within the
entire sample of molars characterized by wear stages 2
and 3 show significant differences in the protocone and
TABLE 2. Between-group comparisons
of relative cusp wear areas of molars with different
wear stages (2 and 3)
Groupsa
Hypocone Protocone Paracone Metacone
Entire sample
NEA
MPHS
UPHS
MHS
Fig. 4. Left M1 of Le Moustier 1: calculation of cusp height
measuring the perpendicular distance between the highest tip point
and the cervical plane (reference plane).
0.441
0.840
<0.001
0.136
0.094
0.051
<0.001
0.101
0.400
0.114
0.229
0.114
Mann-Whitney U test, corrected P values (Bonferroni), and
significant P values (<0.05) are highlighted in bold.
a
Group labels follow Table 1.
TABLE 3. Absolute cusp wear areas in fossil and modern humans
Samplesa (N)
NEA (15)
MPHS (5)
UPHS (7)
MHS (20)
Protocone, area
(mm2), mean SD
23.4
21.7
21.8
17.6
4.6
4.9
4.2
2.5
Paracone, area
(mm2), mean SD
13.8
12.3
14.5
13.6
2.1
4.0
2.1
2.2
Metacone, area
(mm2), mean SD
11.7
10.6
11.8
14.2
2.3
3.9
5.0
2.8
Hypocone, area
(mm2), mean SD
12.9
13.9
11.5
11.5
3.9
5.9
2.6
2.7
a
Group labels follow Table 1.
TABLE 4. Relative cusp wear areas in fossil and modern humans
Samplesa (N)
NEA (15)
MPHS (5)
UPHS (7)
MHS (20)
a
Protocone, area
(%), mean SD
37.5
37.2
37.1
31.1
Group labels follow Table 1.
4.4
4.1
5.8
3.6
Paracone, area
(%), mean SD
22.4
20.6
24.6
27.1
3.3
1.7
2.0
2.5
Metacone, area
(%), mean SD
18.9
17.5
19.1
24.8
2.9
2.6
5.8
3.3
Hypocone, area
(%), mean SD
20.4
23.0
19.3
20.1
4.1
2.5
2.1
3.8
458
FIORENZA ET AL.
TABLE 5. Between-group comparisons
of absolute cusp wear areas
Groupsa
Protocone
NEA
MPHS
UPHS
MHS
Paracone
NEA
MPHS
UPHS
MHS
Metacone
NEA
MPHS
UPHS
MHS
Hypocone
NEA
MPHS
UPHS
MHS
NEA
MPHS
***
1
1
<0.001
***
1
0.248
***
1
1
1
***
1
1
***
1
1
0.083
***
1
1
1
***
1
0.76
***
1
1
UPHS
***
0.111
***
1
***
1
***
1
TABLE 6. Between-group comparisons
of relative cusp wear areas
MHS
***
***
***
***
Mann-Whitney U test, corrected P values (Bonferroni), significant P values (<0.05) are highlighted in bold.
a
Group labels follow Table 1.
The hypocone wear facets are well-developed, whereas
the metacone wear facets are small. In the UPHS group,
the protocone and paracone facets are the largest and
most developed wear cusp areas of the entire occlusal
crown. Metacone and hypocone wear areas are small and
similar in size. Two main wear patterns are found:
PRO>PAR>MET>HYP (3/7) and PRO>PAR>HYP>MET
(3/7). Finally, the contemporary modern humans (MHS)
M1s are characterized by large metacone and paracone
wear facets, less pronounced protocone wear areas (if
compared with the Pleistocene groups) and by small
hypocone facets. The most common wear patterns are
PRO>PAR>MET>HYP (7/20) and PRO>MET>PAR>HYP
(7/20).
Considering the absolute cusp wear areas, the
Neanderthal protocone facets proved to be the largest of
the entire sample examined here (Table 3). MPHS show
smaller protocone and metacone wear areas and hypocone facets slightly larger than those of NEA. The
UPHS sample is characterized by similar protocone wear
areas to those of the MPHS, larger paracone facets than
those of NEA and MPHS, and by smaller hypocone wear
areas than those of NEA and MPHS. Finally, the MHS
group shows a smaller protocone wear area than
those of Pleistocene hominins, the largest metacone
wear area, and the smallest hypocone wear area.
However, the absolute wear area differences are not pronounced, as confirmed by the between-group comparisons, which do not show any significant difference, with
the exception of the protocone wear facets between NEA
and MHS (Table 4).
Taking into account the relative cusp wear areas,
the protocone facets are similar in all the Pleistocene
hominins and smaller in the MHS sample (Table 5).
The paracone wear areas proved to be smaller in the
MPHS and NEA groups, whereas they are larger in
the UPHS and MHS sample. The largest metacone
Groupsa
Protocone
NEA
MPHS
UPHS
MHS
Paracone
NEA
MPHS
UPHS
MHS
Metacone
NEA
MPHS
UPHS
MHS
Hypocone
NEA
MPHS
UPHS
MHS
NEA
MPHS
UPHS
MHS
***
1
1
<0.001
***
1
0.007
***
0.016
***
***
1
0.617
0.586
***
0.03
0.014
***
1
***
***
1
1
<0.001
***
1
0.003
***
0.046
***
***
0.59
1
1
***
0.18
0.78
***
1
***
Mann-Whitney U-test, corrected P values (Bonferroni), significant P values (<0.05) are highlighted in bold.
Group labels follow Table 1.
a
wear areas are found in the MHS group, followed by
the UPHS, NEA, and MPHS sample. Finally, the
hypocone wear areas are strongly developed in the
MPHS group and smaller in the NEA, UPHS, and
MHS sample.
The between-group comparisons show significant
differences in the protocone relative wear areas between
all the Pleistocene groups and the MHS sample (Table
6). Statistically, significant differences are also found in
the paracone relative wear areas between MPHS and
UPHS and between MPHS and MHS. The metacone
relative wear areas display significant differences
between MHS and Pleistocene groups. Finally, the
between-group comparisons of the relative wear areas
developed on the hypocone cusp do not show any level of
significance.
The cusp height shows a general decrease in molars
characterized by a more advanced degree of wear. In
wear stage 2 molars, the NEA group is characterized
by the highest cusps. In wear stage 3 molars, NEA,
UPHS, and MHS display similar cusp height, whereas
the MPHS exhibits the highest cusps (Table 7). The
relationship between cusp height and relative cusp
areas does not show a significant correlation, with
the exception of the paracone in the NEA (r ¼
0.722, P ¼ 0.004) and UPHS sample (r ¼ 0.929,
P ¼ 0.007; Table 8).
The correlation based on the Spearman method
between relative base cusp areas and relative cusp wear
areas is not significantly different in the Pleistocene
hominins with the exception of the NEA protocone (r ¼
0.768, P ¼ 0.001; Table 9). On the contrary, the MHS
sample is characterized by a significant correlation in
the protocone (r ¼ 0.722, P < 0.001), metacone (r ¼
0.544, P ¼ 0.014), and hypocone (r ¼ 0.442, P ¼ 0.052)
cusps (Table 9).
WEAR FACETS ANALYSIS IN Homo sapiens M1s
459
TABLE 7. Cusps height in fossil and modern humans
Samplesa (N)
Wear stage 2
NEA (12)
MPHS (2)
UPHS (4)
Wear stage 3
NEA (3)
MPHS (3)
UPHS (3)
MHS (20)
Protocone, height
(mm), mean SD
Paracone, height
(mm), mean SD
Metacone, height
(mm), mean SD
Hypocone, height
(mm), mean SD
6.4 0.7
6.6 0.5
6.4 0.6
6.7 0.7
6.1 0.7
6.4 1.3
7.1 0.8
6.1 0.9
6.4 1.3
6.3 0.7
6.1 0.1
6.1 1.8
5.1
6.1
5.0
5.1
0.4
1.0
0.6
0.7
5.7
6.2
5.5
5.6
0.2
0.8
0.3
0.6
5.8
6.5
6.2
5.9
0.7
0.6
0.4
0.7
5.0
6.3
5.4
5.1
0.2
0.7
0.7
0.7
a
Group labels follow Table 1.
TABLE 8. Correlation between cusp height
and relative cusp wear areas
Groupsa
NEA
MPHS
UPHS
MHS
Protocone
Paracone
Metacone
Hypocone
0.059
0.517
0.236
0.911
0.004
0.350
0.007
0.977
0.567
1
0.354
0.336
0.466
0.133
0.556
0.515
TABLE 9. Correlation between relative cusp
base areas and relative cusp wear areas
Groupsa
NEA
MPHS
UPHS
MHS
Protocone
Paracone
Metacone
Hypocone
0.001
0.233
0.354
<0.001
0.845
0.45
0.167
0.619
0.304
0.233
0.964
0.014
0.245
0.35
0.236
0.052
Spearman method, significant P values (<0.05) are highlighted in bold.
a
Group labels follow Table 1.
Spearman method, significant P values (<0.05) are highlighted in bold.
a
Group labels follow Table 1.
DISCUSSION
same pattern when analyzing the cusp base areas.
However, in our NEA sample, there is high wear pattern
variability, especially evident in the metacone and hypocone wear facets.
The MPHS specimens included in this study show a
homogenous wear pattern, where PRO>HYP>PAR>MET.
Their occlusal crown is characterized by a development of
large hypocone wear facets and by a strong reduction of
paracone and metacone wear areas. The low variable
wear pattern found in MPHS could be because of the
smaller sample size, or to the fact that all the specimens
(Qafzeh Cave, Israel) most likely belonged to the same
population (Tillier, 1999). Cusp base area studies of the
MPHS M1s have shown a similar pattern to those of
NEA, characterized by a strong enlargement of the hypocone and a pronounced reduction of the metacone (Bailey
2002, 2004; Quam et al., 2009).
The general UPHS cusp wear area pattern is similar
to those found in the MPHS group. However, MPHS and
UPHS differ because the latter group shows a stronger
development of the paracone wear areas and a reduction
of the hypocone facets. Similar results were obtained by
Bailey (2002, 2004), Gómez-Robles et al. (2007), and
Quam et al. (2009), which showed the hypocone reduction in the UPHS specimens. However, in the study of
Bailey (2002, 2004) and Quam et al. (2009), the relative
metacone cusp area is larger than that of the hypocone;
whereas in our study, the degree of wear facet development along the metacone and hypocone slopes of the
UPHS specimens is quite similar.
Finally, in the MHS group the cusp wear facet areas
follow the patterns PRO>PAR>MET>HYP and
PRO>MET>PAR>HYP. The metacone is particularly
developed, whereas protocone and hypocone wear areas
are strongly reduced. Morphometric analyses of MHS
M1s have brought similar results, showing a pronounced
hypocone reduction and an increase of the metacone
Occlusal wear facets vary in number, size, and shape
depending on degree of wear, absolute cusp number, and
tooth morphology (Kullmer et al., 2009). However, the
intragroup comparisons (Table 2) of relative cusp wear
areas did not show any significant difference in molars
(with the exception of the Neanderthal paracone) characterized by wear stages 2 and 3. This result suggests that
during the first dental wear stages the wear pattern differences, reflected by the relative cusp wear areas, are
less pronounced.
The morphology of the lower dentition, together with
the presence of malocclusions (dental disorders characterized by a misalignment of teeth), may influence the
spatial position and development of the wear facets in
the maxillary molars (Fiorenza et al., 2010). However, as
the fossil record is often fragmentary and characterized
by an incomplete dentition, it is difficult to reach a good
sample size for the study of the relationship between
upper and lower teeth. Moreover, malocclusions were
very rare in hunter-gatherer societies before 19th
century, especially in archaic humans (Begg, 1954;
Hunt, 1961; Begg and Kesling, 1977; Corruccinni and
Pacciani, 1989; Proffit and Fields, 2000; Evensen and
Øgaard, 2005). Therefore, we can hypothesize that the
influence of malocclusions in the development of the
wear facets was negligible in the human fossil sample.
Occlusal wear patterns in NEA, MPHS, and UPHS
and in contemporary modern human M1s partially reflect
the cusp pattern found in previous studies (Bailey 2002,
2004; Gómez-Robles et al., 2007; Quam et al., 2009). In
the NEA group, the development of cusp wear areas
follows a general pattern, where PRO>PAR>HYP>MET.
The protocone wear facets are strongly developed,
the metacone wear area is reduced, and the hypcone
facets are relatively large. Bailey (2002, 2004) found the
460
FIORENZA ET AL.
area (Bailey, 2002, 2004; Gómez-Robles et al., 2007;
Quam et al., 2009). Similar to the NEA group, the MHS
sample also shows great variability in cusp wear areas.
However, the between-group comparisons in relative
cusp wear areas show rather different results from
previous morphometric analyses (Bailey, 2002, 2004;
Gómez-Robles et al., 2007; Quam et al., 2009). Although
these studies highlighted that cusp pattern differences
among Pleistocene hominins and modern groups can
largely be attributed to differences in the relative size of
the distal portion of the tooth (Bailey, 2004), our analysis
shows that differences in the wear facet development can
be attributed to the protocone and metacone wear areas.
No differences could be found in the hypocone wear areas.
More importantly, the weak relationship between
wear facet development and cusp size is corroborated by
the absence of correlations found in all the Pleistocene
hominins with the exception of the modern sample.
These results suggest that wear facet development is not
distinctively related to cusp size, agreeing with Janis’s
work (1990), who stated that differences in dental
morphology do not generate differences in occlusal wear
patterns if two taxa have similar diets.
Many studies have shown that differences in tooth
wear in Homo are related to the physical properties of
the ingested food, food preparation techniques, abrasiveness of the environment, and to cultural and nondietary
habits (Molnar, 1972; Kay, 1977; Hinton, 1981; Smith,
1984; Teaford and Walker, 1984; Frayer and Russel,
1987; Janis, 1990; Lucas, 2004; Ungar et al., 2008).
Therefore, the strong correlation found between cusp
size and wear patterns in the modern sample, is probably due to the fact that all the modern specimens studied belong to Khoe-san populations, characterized
by similar dietary and cultural habits. The absence of
major discriminatory factors, such as diet and food preparation methods, leads to similar occlusal wear patterns, which are also reflected through a close
relationship with cusp size.
On the contrary, the Pleistocene groups consist of
specimens characterized by a large geographical, chronological, ecological, and climatic variation, which also
allowed (and necessitated) the exploitation of a greater
variety of food sources. These factors result to be more
important than dental morphological variations in determining the development of the wear facets.
The absence of correlation (with the exception of the
paracone in Neanderthal and UPHS groups) between
cusp heights and cusp wear areas indicates that the
articulation with the lower molars at these wear stages
does not create wear pattern differences. This result
may be due to the fact that only M1s in full occlusion
were selected for this analysis. Moreover, maxillary
first molars exhibit the most stable morphology within
the molar series (Scott and Turner, 1997). The cusp
height-cusp wear area relationship may be stronger in
molars characterized by a great cusp reduction. For
example, the strong distal cusp reduction, often characterizing second and third maxillary molars, may prevent the occlusal contact with the opposing lower
molars. Thus, wear patterns could be strongly influenced by the degree of cusp development, because a
full occlusion would be reached only in more advanced
wear stages.
CONCLUSIONS
The study on the occlusal wear pattern of maxillary
first molars in Late Pleistocene and modern humans has
shown that the cusp size is only of secondary importance
to the development of occlusal wear facets. No wear
pattern differences have been found on the distal portion
of the tooth, and no correlations have been found
between cusp sizes and wear facet areas in the Pleistocene groups. Other factors, such as diet and food preparation methods, are probably more important for the
wear pattern formation, as suggested by previous analyses (Butler, 1952, 1973; Kay, 1977; Janis, 1990).
However, to better interpret the importance of
the ingested food on the formation of tooth wear, this
type of study should be extended to other recent huntergatherer populations characterized by different subsistence strategies, where detailed information on dietary
habits are available.
Finally, a larger sample, including individuals with a
complete dentition, could be used to better understand
the contact relationship between maxillary and mandibular teeth regarding the dynamics of jaw movements,
and their influence on the position and development of
the occlusal wear facets.
ACKNOWLEDGMENTS
The authors thank the following curators and institutions for access to comparative and fossil specimens: Tatiana Baluyeva and Elizavieta Veselovskaya (Institute of
Ethnology and Anthropology, Russian Academy of
Sciences, Moscow), Angiolo Del Lucchese (Museo Preistorico dei Balzi Rossi, Ventimiglia, Italy), Marta Dočkalová
(Moravské Zemské Muzeum, Brno, Czech Republic),
Almut Hoffmann (Museum für Vor- und Frühgeschichte,
Berlin, Germany), Fabio Parenti (Istituto Italiano di Paleontologia Umana, Rome, Italy), Yoel Rak (University
of Tel Aviv, Israel), Chris Stringer and Rob Kruszynski
(Natural History Museum, London, UK), National
Museum of Wales (Cardiff, Wales), Maria Teschler-Nicola
(Naturhistorisches Museum, Vienna, Austria), and Erik
Trinkaus (Washington University, Saint Louis, MO) and
also thank Christine Hemm for technical assistance and
Matt Westwood for copy-editing the manuscript.
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