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Influence of cranial deformation on facial morphology among prehistoric South Central Andean populations.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 130:462–470 (2006)
Influence of Cranial Deformation on Facial Morphology
Among Prehistoric South Central Andean Populations
Matthew P. Rhode1* and Bernardo T. Arriaza2
1
Department of Anthropology, University of Missouri-Columbia, Columbia, Missouri 65201
Centro de Investigaciones del Hombre en el Desierto, Departamento de Arqueologı́a y Museologı́a,
Universidad de Tarapacá, Arica, Chile
2
KEY WORDS
artificial; intentional; South America; face; craniofacial; biodistance
ABSTRACT
Calculating biodistances among South
American populations using cranial measurements is
often hindered, as many available skeletal collections
exhibit deformation. Acknowledging vault modifications,
researchers have sought measurements in other regions
which are unaffected by deformation. In the 1970s, a set
of 10 ‘‘relatively’’ unaffected facial measurements was
identified in Argentinean crania that later became the
basis of numerous South American biodistance studies.
These measurements include: minimum frontal breadth,
bizygomatic breadth, orbit height, orbit breadth, palate
breath, palate length, upper facial height, basion-prosthion length, nasal height, and nasal breadth. Palate
length was excluded from the present analysis due to
considerable measurement error. The suitability of these
measurements in populations other than Argentineans
has not been rigorously tested. Using a sample of 350
prehistoric crania from the Museo Arqueológico San
Miguel de Azapa (MASMA, Arica, Chile), this project
tested the hypothesis that these measurements are unaffected by either annular or tabular deformation. Results
obtained from MANOVA analysis indicate this hypothesis
cannot be fully supported. Among males, only 3 of the 9
measurements are unaffected by either form of deformation (palate breadth, basion-prosthion length, and nasal
breadth), while analysis of females indicates that 4 of the
9 measurements remain unaltered (minimum frontal
breadth, orbit breadth, basion-prosthion length, and nasal
breadth). Additionally, analogous to the vault, facial
measurements display patterns consistent with the deformation applied. Two implications can be drawn from this
research: 1) previous studies using these measurements
must be interpreted cautiously, and 2) researchers using
these measurements must explicitly test their suitability
in each population. Am J Phys Anthropol 130:462–470,
2006. V 2006 Wiley-Liss, Inc.
Deciphering biocultural relationships among past populations continues to be a topic of interest to physical anthropologists, and studies have spanned the gamut using
genetic (blood groups and DNA), linguistic, archaeological,
and osteometric data. Of these sources, cranial measurements, both conventional linear (two-dimensional; 2D) and
coordinate (three-dimensional; 3D) landmark or morphometric data, comprise a majority of these studies. Such
research has as its goal the measurement and interpretation of the phenotypic/genetic relatedness or divergence
among populations or subgroups within a population, using
sets of quantifiable polygenic morphometric traits (Buikstra
et al., 1990; Larsen, 1997). However, influences from confounding factors limit the application of these methods in
some regions. One such factor is cranial deformation, given
the likelihood that deformation skews or alters cranial
measurements. Interpretations derived from such data may
inaccurately reflect underlying genetic relationships, being
spurious associations created by deformation, which may
mirror patterns created by ethnic variation and/or reproductive isolation. This is especially true of South American
materials, where more than 50% of available collections
often exhibit deformation (Allison et al., 1981; Dingwall,
1931; Gerszten, 1993; Gerszten and Gerszten, 1995).
Two types of deformation are recognized: intentional
and unintentional. Intentional deformation is the culturally prescribed practice of artificially modifying ‘‘natural’’
head shape to a more desired form (Anton, 1989a,b;
Dingwall, 1931; Flowers, 1881; Gerszten, 1993; Gerszten
and Gerszten, 1995; Rogers, 1975). Desired head form is
informed by cultural aesthetics, parental desires, and
parental willingness to submit their children to procedures involving the application of boards, pads, bands,
stones, or a combination of elements to the skull during
the first year of life or longer (Dingwall, 1931; Blackwood and Danby, 1955; Rogers, 1975). Unintentional cranial deformation results from a variety of factors, including genetics, hormones, individual nutrition and health,
and preferred sleeping posture (Anton, 1989a,b; Dingwall, 1931; Flowers, 1881; Rogers, 1975).
Two general types of deformed crania are recognized in
South America: 1) annular, circumferential, circular, or
Aymara; and 2) tabular, fronto-occipital, or antero-posterior
(Allison et al., 1981; Dembo and Imbelloni, 1938; Dingwall,
1931; Gerszten, 1993; Gerszten and Gerszten, 1995; Imbelloni, 1924–1925, 1933; Munizaga, 1976; Neumann, 1942;
Rogers, 1975; Romano, 1965; Weiss, 1962). These two forms
can be further subdivided into oblique and erect variants,
C 2006
V
WILEY-LISS, INC.
C
Grant sponsor: University of Nevada, Las Vegas Study Abroad
Grants; Grant sponsor: National Geographic; Grant number: 571296; Grant sponsor: Fondecyt; Grant number: 1950035/1970525.
*Correspondence to: Matthew P. Rhode, Department of Anthropology, University of Missouri-Columbia, 107 Swallow Hall, Columbia,
MO 65201. E-mail: mprgd8@mizzou.edu
Received 24 September 2004; accepted 9 May 2005.
DOI 10.1002/ajpa.20333
Published online 27 January 2006 in Wiley InterScience
(www.interscience.wiley.com).
463
CRANIAL DEFORMATION AND FACIAL MORPHOLOGY
TABLE 1. Nine measurements under analysis
Basion-prosthion length
Maxillo-alveolar length (dropped)
Maxillo-alveolar breadth
Upper facial height
Minimum frontal breadth
Nasal height
Nasal breadth
Orbital breadth
Orbital height
Bizygomatic breadth
Fig. 1. Common MASMA cranial types.
which can be further subdivided into a myriad of subtypes
(Allison et al., 1981; Espoueys, 2004; Gerszten, 1993). For
this paper, a simple classification system delimiting three
cranial types was used (Fig. 1): annular (ANN), tabular (T),
and normal/nondeformed (N), following Anton (1989a,b),
Cheverud et al. (1992), Cheverud and Midkiff (1992), Kohn
et al. (1993), and Rogers (1975).
Common data used in biodistance analysis include linear
and 3D cranial measurements (Howells, 1973, 1989, 1995;
Larsen, 1997; McKeown and Jantz, 2002). Observed variation in such data is assumed to reflect primary genetic relationships between sample populations, ‘‘undiluted’’ by
external factors. Yet, as noted, populations like those from
South America often possess a greater percentage of
deformed than nondeformed crania. When confronted with
collections possessing deformed crania, researchers have
two alternatives: 1) not to perform biodistance analysis
using deformed crania, proceeding with a reduced but
potentially biased sample of nondeformed crania; or 2) to
discover a way to use the deformed crania, which will permit the biodistance analysis to proceed. Given that the first
alternative is often not appealing, researchers have attempted to find ways to make deformed crania usable.
One method used to make deformed crania usable is
to identify regions which are only ‘‘slightly’’ (nonsignificantly) affected by deformation. A review of the literature reveals numerous attempts to define the impacts of
deformation on cranial measurements (Anton, 1989a,b;
Blackwood and Danby, 1955; Bjork and Bjork, 1964;
Cheverud et al., 1992; Cheverud and Midkiff, 1992;
Friess and Baylac, 2003; Kohn et al., 1993; McGibbon,
1965; McNeill and Newton, 1965; Mizoguchi, 1991; Oetteking, 1924; Schendel et al., 1980; Suzuki et al., 1993).
Overall results suggest that most common cranial measurements are altered by deformation to some degree.
The degree and severity of modification vary by population, deformation type, and measurements under study.
BAPR
PRALV
ECMECM
NPR
FTFT
NNS
ALAL
DEC
ORBHGHT
ZYZY
Annular deformation is characterized by lengthening
of the cranial vault and narrowing of medial-lateral
dimensions, leading to increased height and decreased
width measurements (Anton, 1989a,b; Kohn et al., 1993).
Tabular deformation is characterized by vault compression along the sagittal plane, with expansion of mediallateral dimensions. This causes width measurements to
increase, while height measurements are variably affected (Anton, 1989a,b; Cheverud et al., 1992; Cheverud
and Midkiff, 1992).
As the vault is the most significantly altered portion
of the cranium, other regions have received increased
attention in the search for measurements unaffected by
deformation. Of the remaining regions, the facial skeleton
has generated the most research. This attention is tied to
the assumption that facial features are more directly
under genetic (population-specific) and cultural (health,
diet, and subsistence) control (Devor, 1987; Kohn, 1991;
Vandenberg, 1962), and thus are useful in establishing biological relatedness among populations. In South America,
a series of influential publications by Cocilovo (1973, 1975,
1978) profoundly impacted the direction of future biodistance studies in the region. Cocilovo (1975) identified a
set of 10 facial measurements among Argentinean crania
that were shown to be unaffected or ‘‘slightly’’ affected by
deformation (Table 1). This set of 10 facial measurements
was subsequently adopted by researchers, and has been
the basis for numerous South American biodistance studies
over the past 20 years (Cocilovo et al., 1982, 1990, 1995;
Dittmar, 1996; Guillén, 1992; Rivera, 1984, 1991; Rivera
and Rothhammer, 1986, 1991; Rothhammer, 1994; Rothhammer and Silva, 1989, 1990, 1992; Rothhammer et al.,
1981, 1982, 1983, 1984a,b, 1986; Rothhammer and Santoro,
2001).
Upon review of this research, concerns arise over the
use of measurement sets, which differ from study to study.
This may by an artifact of data limitations, but there is an
expectation that researchers would maintain consistency
across publications that often used the same populations.
This discrepancy makes evaluating published results complicated (Sutter, 1997, 2000; Rhode, 2001, 2002). More significantly, there is doubt as to whether the reliability of
these measurements has been fully tested. Specifically, no
published study shows whether the measurements remain
stable in deformed crania other than the Argentineans
originally examined by Cocilovo (1973, 1975, 1978; see
Rhode, 2001, 2002). The present research seeks to address
this concern by testing the hypothesis that 9 of the 10
measurements identified by Cocilovo (1973, 1975, 1978)
are unaffected or are only slightly affected (nonsignificantly) by deformation (annular or tabular) in a prehistoric
Chilean population, and therefore can be used by researchers in biodistance studies of these populations.
464
M.P. RHODE AND B.T. ARRIAZA
TABLE 2. Cranial types studied
Cranial type
Normal
Annular
Tabular
Total
Males
Females
Total
66
45
40
151
54
62
83
199
120
107
123
350
0.46 mm. Further information on the procedures used to
test measurement replicability can be found in Rhode
(2001). Combined, these results indicate random, nondirectional error, reflecting a consistent measurement technique. Interobserver error could not be examined due to
time constraints in the field.
Missing data
MATERIALS AND METHODS
Sample
The sample used to test the hypothesis of measurement
stability under deformation included several collections from
the Museo Arqueológico San Miguel de Azapa (Arica, Chile).
This is the same collection used by Rothhammer and
Santoro (2001) in a biodistance study of Azapa Valley
populations. The sample consisted of 350 crania representing 18 archaeological sites (8 coastal and 10 inland)
and several cultural groups spanning a period of roughly
7,000–8,000 years. Additional background information
on these sites can be obtained in Rhode (2001). Cases
were selected for analysis based on the following criteria.
1) Only complete or nearly complete crania were used. 2)
Crania were from individuals over 17 years old. 3) Crania with obvious pathologies or trauma were excluded.
4) Approximately equal numbers of males and females
(151 males and 199 females) were used to permit analysis of sexual dimorphism. Each individual was coded for
sex and deformation type prior to collecting measurements. Sex determinations were aided by the fact that
many skeletons were formerly mummified and had been
sexed using preserved external genitalia.
Cranial deformation was scored visually, following the
system of Dembo and Imbelloni (1938). Following Rogers
(1975) and Anton (1989a,b), only three cranial types
were recognized: normal (N), annular (ANN), and tabular (T) deformation (Fig. 1). Of the 350 crania studied,
230 (65.6%) exhibited deformation. One hundred and
twenty crania were classified as normal/none, 107 displayed annular deformation, and 123 were classified as
exhibiting tabular deformation. Table 2 provides a
detailed breakdown of cranial types used.
Measurements
Table 1 lists the 10 linear measurements collected
from each cranium, which were identified as unaffected
by Cocilovo (1973, 1975, 1978). Initially, all 10 of Cocilovo’s measurements were to be examined, but palate
length (pr-alv) was excluded from analysis early during
data collection because it was found to be an inherently
difficult measurement to replicate, as noted by Heathcote (1981). Specifically, determining the location of
alveolon (alv) is problematic, as it lacks a defined anatomical landmark.
After each of the 350 crania had been measured by
M.P.R., a subset of 51 (25 males and 26 females), or
14.6%, of the sample was randomly selected and remeasured to conduct intraobserver error analysis, as recommended by Buikstra and Ubelaker (1994). The time
lapse between initial and secondary measurement periods varied from 1 week to 1 month. Comparisons between the first and second measurement sessions across
all measurements produced Pearson correlations averaging r ¼ 0.96, an average mean difference of measurement of 6 0.02 mm, and an average method error of
Missing data accounted for approximately 5% of the
sample, indicating that data replacement was possible
(Allison, 2002; Little and Rubin, 1987). Factor analysis
of the missing values did not show patterning with age,
sex, or health indicators, suggesting the pattern of missing data could be considered missing at random (MAR)
(Allison, 2002; Little and Rubin, 1987, 1989; Little and
Schenker, 1995; Schafer, 1997, 1999a,b; Schafer and
Olsen, 1998). Missing data patterns by deformation type
were not investigated, and therefore it was not possible
to establish whether the data were MAR with respect to
the variables of interest (Holt and Benfer, 2000). Several
approaches are available for analyzing and imputing
missing data (e.g., Allison, 2002; Little and Rubin, 1987).
One common method is complete case analysis. If used,
this method would have reduced the data set by 50%,
possibly creating a substantially biased sample. Other
common methods include mean replacement or linear
regression, which may have created an overly homogenous data set, obscuring integral relationships. The
method selected to address missing data in this project
was the multiple imputation procedure of Schafer (1997),
performed using the NORM 2.3 program (Schafer,
1999a,b). The NORM program is designed to analyze
normally distributed continuous data. For this data set,
the only non-normal data were sex and deformation
type, which were determined for all crania. The only
missing data were measurements from individuals who
exhibited damaged crania. Given these conditions, it is
acceptable to use the NORM program for missing data
analysis. Multiple imputation uses an expected maximization procedure as the first approximation of the missing data, and then performs data augmentation using a
Monte Carlo Markov chain procedure, which creates
multiple complete data sets that progressively (iteratively) converge towards a point of unity, where the variation between imputed data sets becomes negligible.
Diverging from the procedures of Schafer (1999a,b), the
final imputed data matrix, exhibiting the least variation,
was chosen as the data set to be studied, instead of
using 4 or 5 selected during imputation. Males and
females were not separated during this procedure, meaning that the imputed data set may exhibit slight homogenization, but less than could occur using mean replacement or linear regression.
Statistical analyses
Exploratory data analysis performed using SPSS 8.0
and 12.0 indicated that the nine measurements did not
violate normality assumptions individually, by sex, or by
deformation based on analysis of box plots, spread vs.
level plots, and Q-Q plots (Norušis, 1988). Though several values for individual measurements could be classified as outliers, none were extreme outliers, and all 350
individuals were used in subsequent analyses. Table 3
presents summary statistics created during this analysis
for the nine measurements by sex and deformation type.
465
CRANIAL DEFORMATION AND FACIAL MORPHOLOGY
TABLE 3. Summary statistics of nine measurements under analysis
Male
Measurement
Deformation
type
Mean
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
98.6
100.3
99.1
61.6
62
62.6
69.4
71.4
70.8
91
88.3
88.7
50.4
51.7
50.2
24.4
24.7
24.7
38.6
39.5
38.8
34.7
36.3
35.9
136.9
135.4
138.4
BAPR
ECMECM
NPR
FTFT
NNS
ALAL
DEC
ORBHGHT
ZYZY
Female
SD
Deformation
type
Mean
SD
5.2
5.1
4.2
3.3
3.4
3.7
4.4
4.2
4.2
4.8
5.3
5.6
3.4
2.5
2.9
1.6
1.9
1.6
1.7
1.7
1.7
1.9
1.9
2.1
5.6
5.7
4.9
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
Normal
Annular
Tabular
95.4
96.9
95.9
59.4
59.8
60.9
66.2
68.3
68.5
87.3
86
87.5
47.1
49.4
48.6
23.8
24.3
24.2
38.1
38
38.2
34.3
36.1
35.8
127.9
127.6
131.5
4.7
3.9
4.4
3.3
2.8
2.9
4.3
3.3
4.4
3.8
5.3
4.3
2.6
2.5
2.8
1.8
1.6
1.6
1.5
1.6
1.7
1.8
1.8
2
4.5
4.7
4.7
TABLE 4. Male and female multivariate MANOVA1
Male
Deformation type
Female
Deformation type
1
Test
Value
F-value
Hypothesized df
Error df
Significance
Pillai’s trace
Wilks’ lambda
0.41
0.63
4.00
4.05
18
18
282
280
0.00
0.00
Pillai’s trace
Wilks’ lambda
0.43
0.61
5.81
5.80
18
18
378
376
0.00
0.00
Significant results in bold.
The statistical method chosen to test the effect of
deformation on the nine facial measurements was multivariate analysis of variance (MANOVA) under the general linear model (GLM) multivariate procedures module
of SPSS 8.0 and 12.0. This procedure is an extension of
the general ANOVA, for questions with several dependent variables measured in two or more samples (Norman
and Striener, 2000; Norušis, 1998; Sokal and Rohlf,
1995). This method avoids spurious results caused by
repeated testing, which would occur with multiple ttests, taking the correlation among dependent variables
into consideration (Norman and Striener, 2000). In this
study, the nine facial measurements were the dependent
variables, and the independent variables were deformation types (normal, annular, and tabular). During preliminary analyses (not presented), sexual dimorphism
was found to be a significant influencing factor on all
variables, and male and female data sets were subsequently separated during the MANOVA analysis.
RESULTS
Before running the MANOVA, a Box’s M test of covariance matrix equality was performed. Results did not
reach significance, with F ¼ 1.13 and P ¼ 0.09, indicating that the assumption of covariance matrix equality
can be supported. These results also indicate that the
MANOVA model was not suspect, meaning the analysis
could reasonably proceed.
The first MANOVA analysis examined the overall relationship between measurements (dependent variables)
and cranial types (independent variables). The results of
this test, presented in Table 4, indicate that variation in
cranial type significantly altered measurements, with a
Pillai’s trace and Wilk’s lambda values of P ¼ 0.00 for
males and females. The low Pillai’s trace and high Wilk’s
lambda values from Table 4 signify the presence of
strong interactions among dependent and independent
variables. These results by themselves imply that the
hypothesis of measurement stability across deformation
types cannot be supported in this population. Yet additional tests were needed to identify whether all measurements were equally affected by deformation, or whether
effects varied by deformation type.
Following the basic multivariate tests, a more detailed
analysis of between-subjects effects was carried out for
each measurement for each of the three cranial types.
The results of this test, presented in Table 5, indicate
466
M.P. RHODE AND B.T. ARRIAZA
TABLE 5. Male and female between-subjects
effects by deformation1
Dependent
variable
Type
III SS
df
Mean
square
F-value
Significance
Males
FTFT
ORBHGHT
ZYZY
DEC
ECMECM
NPR
BAPR
NNS
ALAL
236.79
76.62
191.96
270.03
25.35
118.20
83.93
60.43
4.38
2
2
2
2
2
2
2
2
2
118.39
38.31
95.98
13.51
12.67
59.10
41.97
30.21
2.19
4.48
9.80
3.20
4.71
10.09
3.22
1.71
3.31
0.74
0.01
0.00
0.04
0.01
0.34
0.04
0.18
0.04
0.48
Females
FTFT
ORBHGHT
ZYZY
DEC
ECMECM
NPR
BAPR
NNS
ALAL
84.27
114.20
693.69
0.68
83.25
182.80
68.58
1530.09
8.50
2
2
2
2
2
2
2
2
2
42.13
57.10
346.85
0.34
41.63
91.40
34.29
76.55
4.25
20.07
16.22
160.03
0.13
4.68
5.56
1.80
10.89
1.54
0.13
0.00
0.00
0.88
0.01
0.00
0.17
0.00
0.22
1
Fig. 3. Male measurements affected by deformation.
Significant results in bold.
Fig. 4. Female measurements not affected by deformation.
Fig. 2. Male measurements not affected by deformation.
that only 3 of 9 male measurements (palate breadth,
basion-prosthion length, and nasal breadth) could be
considered to remain stable under deformation. Figure 2
graphically displays the unaffected male measurements,
and Figure 3 the affected male measurements. For the
female data, only 4 of the 9 measurements (minimum
frontal breadth, orbit breadth, basion-prosthion length,
and nasal breadth) remain stable under deformation.
Figure 4 graphically presents the unaffected female
measurements, and Figure 5 the affected female measurements. Examining these tables and figures, it is clear
that fewer than half of the measurements of Cocilovo
(1973, 1975, 1978) may be considered unaffected by
deformation in this population.
Among the female significance values (Table 5), all
measurements were either strongly significant or nonsignificant. Yet among male values this was not the case,
as several measurements (bizygomatic breath, nasal
height, and upper facial height) can be considered marginally significant (P ¼ 0.04). These measurements may
possibly be more affected by one type of deformation
than the other, differences unable to be highlighted
though this analysis. Between-subjects effects reveal no
information concerning how a given measurement is
altered by deformation. Post hoc testing using multiple
comparisons can clarify these relationships.
Post hoc tests (similar to repeated t-tests) were performed on each cranial type combination (normal-annular, normal-tabular, and annular-tabular) across all nine
measurements for males and females, to determine the
direction and magnitude in which measurements were
altered by deformation, and to clarify male measurement
relationships. Repeated testing can be problematic, because increasing the number of comparisons reduces the
likelihood of at least one comparison being wrongly
declared significant, thus committing a type II error. Post
hoc tests account for this possibility by applying a correction factor to reduce the possibility of inflated probability
values (Legendre and Legendre, 1998; Sokal and Rohlf,
1995). Of several correction factors, Tukey’s honestly sig-
CRANIAL DEFORMATION AND FACIAL MORPHOLOGY
Fig. 5. Female measurements affected by deformation.
nificant difference (HSD) was selected for this study. This
is a more liberal test than the more commonly used but
conservative Bonferroni test (Norman and Striener, 2000).
Table 6 presents the results of the multiple comparisons
analysis.
Reviewing the results in Table 6, the most obvious
aspect is that none of the nine measurements can be
considered significant across all cranial types for either
males or females. Focusing on the three male measurements considered marginally significant, this patterning
explains the observed marginal P-values. Only the annular-tabular comparison was significant for bizygomatic
breadth, while the annular-normal and tabular-normal
comparisons were nonsignificant. In other words, bizygomatic breadth can be used to differentiate annular from
tabular crania, but not normal from deformed crania.
For upper facial height, only the normal-annular comparison was significant, indicating that an increase in
upper facial height can be used to distinguish normal
and annular crania. Further, this suggests that in these
populations, tabular and annular deformation cause
upper facial height to be increased among males. The
third questionable male measurement, nasal height,
displayed a more interesting result, which illustrates
that none of the three comparisons performed was significant with adjusted P-values. The normal-annular (P
¼ 0.07) and annular-tabular (P ¼ 0.06) comparisons
nearly reach significance, yet given the combined unlikelihood of these three differences, it is acceptable to
include this measurement among those considered nonsignificant. However, for the purposes of this paper, it is
included among the measurements considered significantly affected.
DISCUSSION
The patterns obtained from the MANOVA analysis can
more easily be assessed by examining Figures 2–5. Overall, it appears that cranial deformation has a variable
but definitive impact on the facial skeleton. This impact
corresponds both to the type of deformation applied and
culturally prescribed factors (severity and/or apparatus)
related to the deformation procedure. Specifically, the
patterns noted in Table 6 and Figures 2–5 correspond
467
well with those noted by previous researchers regarding
the general consequences of deformation. Briefly, annularly deformed crania exhibit increased length measurements seen in the nasal and orbital heights, while reducing width measurements is evidenced in bizygomatic
breadth and minimum frontal breadth. Palate breadth
can be included in this list for females, but not males.
This result may reflect variation across the sexes in performing deformation within these Chilean groups, or it
may correspond to variation in deformation severity
(data collected but not included in this analysis). The
facial skeletons of tabularly deformed crania similarly
follow patterns described in the literature, with increased width measurements evidenced by bizygomatic
breadth. Minimum frontal breadth varies with tabular
deformation in males but not females, further suggesting cultural differences in deformation practices. Height
measurements in tabular crania are increased, paralleling the change noted with annular deformation.
Two of the measurements unaffected by deformation
were common to both sexes: basion-prosthion length and
nasal breadth. The centralized placement of these measurements suggests the presence of an underlying structure to the human skull oriented along the inferior sagittal plane. Many of the unaffected measurements, with
the exception of minimum frontal breadth (among
females), are located centrally in the cranium, suggesting that both types of deformation have a greater effect
on peripheral cranial structures, a finding which supports Anton (1989a,b). The differences observed between
males and females can be explained through either of
two hypotheses. The variation noted in measurements
between males and females may reflect some underlying
cultural aesthetics in deformation across the sexes. If
this were the case, it would explain why minimum frontal breadth was unaffected in women but not men. Further, if males preferentially had greater force applied
to the frontal portion of their skulls during tabular
deformation, the pattern observed would be expected.
Alternatively, given the infinite range of possible head
forms, these significance differences may simply reflect
the broad grouping methodology used, in which several
deformation types and severities were combined, obscuring sex-limited expression in deformation subtypes and
severity not addressed in the present research.
CONCLUSIONS
For this sample of several prehistoric Chilean populations, out of the original nine measurements of Cocilovo
(1973, 1975, 1978) under consideration, only three male
measurements (palate breadth, basion-prosthion length,
and nasal breadth) and four female measurements (minimum frontal breadth, orbit breadth, basion-prosthion
length, and nasal breadth) can be considered stable or
unaffected by either annular or tabular cranial deformation. This means that even if these measurements
exhibit some influence caused by the biomechanical
forces used to modify the shape of the cranium, effects
noted in these measurements are not significant with
the sample size used. The remaining six male and five
female measurements show significant effects by deformation, varying with cranial form.
The obtained results suggest that caution is warranted
in using these nine cranial measurements in biodistance
studies in any population that displays intentional deformation. Clearly the original hypothesis that all nine cra-
468
M.P. RHODE AND B.T. ARRIAZA
TABLE 6. Male and female Tukey’s HSD multiple comparisons
Male1
FTFT
ORBHGHT
ZYZY
DEC
ECMECM
NPR
BAPR
NNS
ALAL
1
2
3
Deformation
type2
Mean
difference
Standard
error
Significance3
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
62.71
62.28
60.43
61.59
61.20
60.39
61.47
61.54
63.01
60.98
60.21
60.78
60.47
61.00
60.54
62.00
61.42
60.59
61.76
60.52
61.24
61.28
60.23
61.51
60.31
60.37
60.06
0.99
10.03
0.99
0.38
0.40
0.43
10.06
1.10
1.19
0.33
0.34
0.37
0.66
0.68
0.74
0.83
0.86
0.93
0.96
0.99
10.07
0.58
0.61
0.66
0.33
0.34
0.37
0.02
0.07
0.02
0.00
0.01
0.63
0.35
0.34
0.03
0.01
0.81
0.09
0.76
0.31
0.75
0.04
0.23
0.80
0.16
0.86
0.48
0.07
0.92
0.06
0.62
0.52
0.98
Female1
FTFT
ORBHGHT
ZYZY
DEC
ECMECM
NPR
BAPR
NNS
ALAL
Deformation
type2
Mean
difference
Standard
error
Significance3
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
N vs. Ann
N vs. T
Ann vs. T
61.33
60.12
61.45
61.88
61.51
60.37
60.34
63.60
63.94
60.028
60.10
60.13
60.38
61.48
61.10
62.05
62.22
60.17
61.50
60.52
60.97
62.27
61.51
60.77
60.50
60.42
60.08
0.84
0.79
0.76
0.35
0.33
0.31
0.87
0.81
0.78
0.30
0.28
0.27
0.56
0.52
0.50
0.76
0.71
0.68
0.81
0.76
0.73
0.49
0.46
0.45
0.31
0.29
0.28
0.25
0.99
0.14
0.00
0.00
0.47
0.92
0.00
0.00
1.00
0.93
0.88
0.78
0.01
0.07
0.02
0.00
0.96
0.16
0.77
0.38
0.00
0.00
0.20
0.23
0.31
0.95
Unaffected measurements in bold.
N, normal; Ann, Anular; T, Tabular.
Significant comparisons in italic.
nial measurements could be used in Chilean populations
has been refuted. Moreover, these results cast serious
doubts on the conclusions presented in previous biodistance studies of Chilean populations. Ultimately, those
researchers wanting to use this set of measurements,
would be well advised to explicitly test their suitability
and stability in each population before proceeding with
data analysis.
These cranial measurements and others commonly collected are still of value, and can be used to obtain insights into individual or population-level research questions, but only when used in combination with other
sources such as geographic, chronological, and archaeological data, or health, subsistence, activity, and status
indicators. Biodistance studies seeking to assess genetic
differences between and among populations cannot use
craniometric variables when the populations in question
performed cultural modifications of the cranium. However, those measurements that are found to vary significantly with a given type of deformation may prove useful
in measuring the combined results of reproductive and
cultural isolation, which probably accounts for their
overall interpretability in characterizing biological populations, which are also ethnic groups.
ACKNOWLEDGMENTS
The authors thank the following individuals and organizations for their assistance during this project: the Museo
Arqueológico San Miguel de Azapa researchers Leticia
Latorre and Vivien Standen, University of Nevada at Las
Vegas Study Abroad Grants, and University of Nevada at
Las Vegas Summer Scholarships. The authors also thank
the anonymous reviewers who provided constructive
criticism and valuable suggestions.
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