AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 134:251–262 (2007)

The Influence of Artificial Cranial Vault Deformation on the Expression of Cranial Nonmetric Traits: Its Importance in the Study of Evolutionary Relationships Mariano C. Del Papa* and S. Ivan Perez Divisio´n Antropologı´a, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata (1900), Argentina KEY WORDS

biological distances; genealogical analysis; geometric morphometrics

ABSTRACT Nonmetric cranial traits have been commonly used in evolutionary relationship studies. They develop during the growth and development of an individual, and for this reason its expression presents different sources of genetic and nongenetic variation. However, the use of these features in evolutionary relationship studies carries the implicit assumption that much of the nonmetric trait variation is essentially genetic. Among the nonheritable factors, cranial vault deformation has been the most studied in human populations. Because of the widespread distribution and elevated rate of artificial cranial vault deformation found in America, and the importance of nonmetric traits in evolutionary relationship studies in this area, the objectives of this paper are as follows: (a) to study the influence of artificial cranial vault deformation on the presence of nonmetric

traits within samples of human craniofacial remains; and (b) to establish artificial cranial vault deformation influence on evolutionary relationships between local populations on a regional scale. Our results indicate that artificial cranial vault deformations alter the variation and covariation of metric and nonmetric traits in some samples. Wormian bones, placed in cranial vault sutures, are the most influenced by this factor. However, our results suggest that when all nonmetric traits were used the artificial cranial vault deformation did not influence the basic pattern of variation among samples. The exclusion or inclusion of wormians bones in evolutionary relationships analysis did not modify the results, but using only wormians bones lead to inconsistent results indicating that these traits have little value on these kind of studies. Am J Phys Anthropol 134:251–262, 2007. V 2007 Wiley-Liss, Inc.

Nonmetric cranial traits have been commonly used in biological analyses, especially on evolutionary relationship studies, since the end of the 1950 decade (Laughlin and Jørgensen, 1956; Brothwell, 1958; Berry, 1963; Berry and Berry, 1967; Sjøvold, 1973; Green and Suchey, 1976; Hauser and De Stefano, 1989; Saunders, 1989; Pardoe, 1991; Hanken and Hall, 1993; Ishida and Dodo, 1993; Hanihara et al., 2004; Sutter and Mertz, 2004; among others). These traits have been found in most mammal skeletons (and they might be present in all vertebrates’ skeleton probably; Sjøvold, 1973; Saunders, 1989; Hanken and Hall, 1993) and have been intensely studied on human populations (Hauser and De Stefano, 1989; Saunders, 1989). They develop during the growth and development of an individual (on humans this happens particularly between the second month of embryonic life and the early postnatal period) (Berry and Seable, 1963; Pucciarelli, 1974; Cheverud and Buikstra, 1981; Richtsmeier and McGrath, 1986; Barnes, 1994; Lieberman et al., 2000a), and for this reason, its expression presents different sources of variation (i.e. genetic, epigenetic, maternal, and environmental; Atchley and Hall, 1991). Thus, these traits do not ensue a simple Mendelian pattern of inheritance, and to describe the nature of its genetic control, Gru¨neberg (1951, 1963) has argued that skeletal nonmetric traits are quasi-continuous. Multiple genes with small and additive effects are generally involved in the development of these traits, and the presence of a trait in the phenotype is determined by physiological—or other developmental—thresholds (Sjøvold, 1973; Saunders, 1989). However, the use of

these features in evolutionary relationship studies carries the implicit assumption that much of the nonmetric trait variation is essentially genetic (Berry and Berry, 1967; Sjøvold, 1973; Saunders, 1989). In this sense, different studies (Self and Leamy, 1978; Cheverud and Buikstra, 1981; Richtsmeier and McGrath, 1986; among others) have shown that there is considerable genetic variation (i.e. high heritability values) in cranial nonmetric traits, although these values vary markedly from one population to another (Richtsmeier and McGrath, 1986). Beyond a considerable genetic variation, various environmental and maternal factors can also affect the expression of nonmetric traits (e.g. nutrition; Saunders, 1989) in an extremely variable way among populations. Regarding the nonheritable factors, cranial vault deformation has been the most studied on human populations

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WILEY-LISS, INC.

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Grant sponsors: Doctoral Fellowship Argentine Government (CONICET), Universidad Nacional de La Plata. *Correspondence to: Mariano C. Del Papa, Divisio´n Antropologı´a, Museo de La Plata, Paseo del Bosque s/n, La Plata (1900) Argentina, 0054-221 4534908. E-mail: [email protected] Received 16 May 2006; accepted 29 April 2007 DOI 10.1002/ajpa.20665 Published online 27 June 2007 in Wiley InterScience (www.interscience.wiley.com).

Lehmann-Nitsche (1910); Catalog of MLP and ME Later late Holocene

Catalog of ME Later late Holocene

Later late Holocene

Lehmann-Nitsche (1910); Catalog of MLP and ME Lehmann-Nitsche (1910) Later late Holocene

Lehmann-Nitsche (1910); Catalog of ME Early late Holocene

Later late Holocene

ND5 non-deformed; D5 deformed. a See Perez (2007).

ND: 9; D: 7 ND: 11; D: 8 SJ

ND: 4; D: 16 ND: 10; D: 7 CV

Calchaqui Valley (North-West Argentina) San Juan (North Cuyo)

ND: 8; D: 9 ND: 9; D: 8 LP

ND: 6; D: 15 ND: 5; D: 14 SB-IG

San Blas and Isla Gama (North-East Patagonia) La Pampa (South-West Pampa)

ND: 18; D: 17 NR

ND: 17; D: 18

Slight compression in the lambda area Compression in both occipital and frontal regions, as well as slight expansion in the posterior area of parietal bones Slight compression in the lambda area Slight compression in the lambda area Slight compression in both the occipital and frontal regions Slight compression in both the occipital and frontal regions ND: 21; D: 8 ND: 25; D: 18 ChR

Chubut River Valley (Central-East Patagonia) Negro River Valley (North-East Patagonia)

Deformationa Females Males

TABLE 1. Studied samples

Period

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Abbr.

(Ossemberg, 1970; Sjøvold, 1973; Konigsberg et al., 1993; O’Loughlin, 2004). Although it has been proved that the artificial cranial vault deformation may modify the genetic expression of some nonmetric traits (e.g. ossicles or wormians bones; Ossemberg, 1970; Pucciarelli, 1974; O’Loughlin, 2004), most of these investigations have given contradictory results when establishing the importance of this influence in genealogical analyses. These contradictions are probably due to the fact that in most studies the variation between deformations and between populations were not discriminated correctly (Konigsberg et al., 1993), and also because the degree of the deformation influence can be variable among populations. Artificial cranial vault deformation was a widespread cultural phenomenon in several regions of the world, and particularly in America during prehistoric times (Hrdlicka, 1912; Imbelloni, 1933; Dembo and Imbelloni, 1938). On the late XIX and early XX centuries numerous studies were performed to classify cranial deformation (e.g. Gosse, 1855, 1861; Broca, 1878, 1879; Topinard, 1879; Hrdlicka, 1912; Imbelloni, 1925; Dembo and Imbelloni, 1938; Neuman, 1942). These traditional classifications were mainly generated by pooling crania that presented similarities in the morphology of its external

Sample

Fig. 1. Map showing the geographic localization of the samples of crania analyzed.

Lehmann-Nitsche (1910)

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References

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253

Fig. 2. No-metric traits and allocated landmarks (n) and semilandmarks (l) registered on craniofacial structures. Abbreviators in Table 2. Drawing by Marina Perez.

vault (Imbelloni, 1925). Because of the morphoscopic techniques applied and the typological approach (Hull, 1992; Sober, 1992) that characterized this early investi-

gative phase in anthropology, significant bias was introduced when analyzing variation in artificial cranial vault deformation. Besides building classifications, the early

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M.C. DEL PAPA AND S.I. PEREZ TABLE 2. Twenty-two nonmetric cranial traits examined in this study

Nonmetric cranial traits name c

Metopic Suture Epipteric Bonec Coronal Ossiclec Sagittal Ossiclec Apical Bonec Lambdoid Ossiclec Asterionic Bonec Parietal Notch Bonec Mastoid Foramenc Inca Bonec Foramen Ovale Incompletec Foramen Spinosum Incompletec Condylar Canalc Divided Hypoglossal Canalc Pterygo-spinossum Bridge or Spurc Pterygo-alar or Bridge or Spurc Maxillary torusc Infraorbital Suturec Foramen at the supraorbital marginc Multiple Infraorbital Foraminac Notches at the supraorbital marginc Trochlear Spurd

Regiona

Abbr. MT EB CO SO AB LO AsB PNB MF IB FOI FSI CC DHC PsBS PaBS MTo IS FSM MIF NSM TS

Cranial Cranial Cranial Cranial Cranial Cranial Cranial Cranial Cranial Cranial Base Base Base Base Base Base Face Face Face Face Face Face

vault vault vault vault vault vault vault vault vault vault

Originb Hypostotic Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Vessel and nerve – Hypostotic Hypostotic Vessel and nerve Hyperostotic Hyperostotic Hyperostotic Hyperostotic Hypostotic Vessel and nerve Vessel and nerve Vessel and nerve Hyperostotic

a

Corruccini (1976). Hanihara and Ishida (2001a–e). Buikstra and Ubelaker (1994). d Ossenberg (1970). b c

studies were also interested in the influence of cranial vault deformation on human craniofacial variation analysis (Imbelloni, 1925; Dembo and Imbelloni, 1938). Likewise, more recent studies (second half of XX century) have been primarily interested in the effects of cranial vault deformation over craniofacial growth and development (e.g. Corruccini, 1976; Richtsmeier et al., 1984; Anto´n, 1989; Cheverud et al., 1979, 1992; Kohn et al., 1993; Konigsberg et al., 1993; Anto´n and Weinstein, 1999; Frieß and Baylac, 2003), centering their analyses upon the traditional classification, without focusing on the overall variation of cranial vault deformation. Because of the widespread distribution and elevated number of artificial cranial vault deformation in America, and the importance of nonmetric traits in genealogical studies for this area, the objectives of this paper are as follows: (a) to study the influence of artificial cranial vault deformation over the presence of nonmetric traits within samples of human craniofacial remains (Fig. 1); and (b) to establish the artificial cranial vault deformation influence on evolutionary relationships between local populations over a regional scale (Fig. 1). The cranial variation related to artificial deformation of human craniofacial remains will be analyzed by means of geometric morphometric methods (Marcus, 1990; Rohlf, 1990a; Rohlf and Marcus, 1993). The main advances of geometric morphometrics over traditional approaches (Reyment et al., 1984; Marcus, 1990) lies on the development of powerful statistical methods based on models for shape variation of an entire configuration of points corresponding to the locations of morphological landmarks (Bookstein, 1991; Rohlf, 1999, 2000) and semilandmarks (Bookstein, 1997). This allows us to contrast previous studies dealing with cranial deformations and nonmetric traits using a new, and more objective and powerful procedure.

MATERIALS AND METHODS Samples The six samples of adult human remains included in this study correspond to male and female individuals of Patagonia, Pampa, Cuyo, and Northwest regions of Argentina (Fig. 1; Table 1). Two samples from Patagonia (Negro and Chubut River Valley) were used in all analyses, while the other four samples were only used to evaluate our second objective (Table 1). The skulls analyzed are complete and they were pooled into samples according to geographical location and sex (Table 1). These samples are housed at the Divisio´n Antropologı´a of the Facultad de Ciencias Natural y Museo UNLP (MLP) and Museo Etnogra´fico ‘‘Juan B. Ambrossetti’’ of the Facultad de Filosofı´a y Letras UBA (ME), Argentina.

Nonmetric traits Twenty-two nonmetric traits (Fig. 2a–e; Table 2; Ossenberg, 1970; Buikstra and Ubelaker, 1994) were recorded (scored as being either ‘‘present’’ or ‘‘absent’’) for all samples by one of us (MCD). While observations were made for each side when dealing with bilateral traits, the ‘‘individual count’’ method was used; if a trait was present on either of both sides, it was scored as present (Dodo, 1974; Turner and Scott, 1977; Sutter and Mertz, 2004). An aspect of this scoring procedure is that trait frequencies may be biased by poor preservation (Konigsberg, 1987; Sutter and Mertz, 2004), however given the excellent preservation of the skull sample examined in this study, such biases are negligible. For analytic purposes we pooled the nonmetric cranial traits using two criteria: first we divided them with a regionbased criterion as face, cranial vault and basicranium— or base—traits (Corruccini, 1976) and second, according to origin-based criterion (Ossemberg, 1970; Dodo, 1974;

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TABLE 3. Variation values to metric cranial vault and nonmetric traits. The individuals nondeformed (ND) and deformed were determined in base to the first RW of lateral morphology (see below)

ChR male all ChR male ND ChR female all ChR female ND NR male all NR male ND NR female all NR female ND

Foote cranial vault distance procrustes

Variance of nonmetric traits proportions

0.0008 0.0008 0.0007 0.0006 0.0017 0.0006 0.0015 0.0008

0.111 0.100 0.090 0.089 0.093 0.082 0.093 0.084

Hauser and De Stefano, 1989; Hanihara and Ishida, 2001a–e), most of nonmetric traits were classified as hipostotic, hiperostotic, vessel, and nerve and wormians (or ossicles).

Geometric morphometrics For morphometric analyses the individuals were positioned in the Frankfurt plane and the digital images were obtained from the crania in lateral (left side) norm with an Olympus Camedia C-3030 digital camera. Coordinates for two landmarks n [nasion (Buikstra and Ubelaker, 1994) and postmastoid (intersection of occipital bone contour and mastoid process)] and 78 semilandmarks (l) were recorded (Fig. 2f) by one of us (SIP). The digital images of the specimens were processed with the MakeFan6 software (Sheets, 2003). MakeFan6 is a tool that places alignment ‘‘fans’’ at equal angular displacements along a curve, to permit a more regular placement of semilandmarks coordinates. The landmarks and semilandmarks coordinates were registered by means of the tpsDIG 1.40 software (Rohlf, 2006). Cranial semilandmarks in lateral norm were aligned using the sliding semilandmark method proposed by Bookstein and Green (Green, 1996; Bookstein, 1997). This operation extends the generalized procrustes analysis (GPA) (Gower, 1975; Rohlf and Slice, 1990; Rohlf, 1990b): in addition to optimally translating, scaling, and rotating landmarks, the semilandmark points are slid along the outline curve until they match as well as possible the positions of corresponding points along an outline in a reference specimen (Adams et al., 2004). This is done because individual points in the curves are not claimed to be homologous from subject to subject. Consequently the variation along tangent directions is not informative and only the coordinate perpendicular to the outline carries information about differences between specimens or groups (Bookstein, 1997; Bookstein et al., 2002). In this study semilandmarks were slid along their respective curves to minimize the Procrustes distance between the subject and a reference (Sampson et al., 1996; Bookstein et al., 2002; Sheets et al., 2004; Perez et al., 2006), using Semiland6 software (Sheets, 2003).

Analyses Shape variation related to deformation within Negro and Chubut River Valley samples was evaluated using Foote’s (1993) disparity measurement, which is defined as morphometrics variance or disparity D 5 S (di2)/(n 2 1) where di represents the specimens’ distance to the group centroid. Disparity was measured using DisparityBox6

Fig. 3. Relative warps analysis of lateral norm for the male (a) and female (b) Chubut River Valley samples.

software (Sheets, 2003), which uses the Partial Procrustes distance as di measure (Zelditch et al., 2004). The difference amidst proportions of nonmetric cranial traits within these samples was established by calculating the variance. Thin-plate spline analysis (Bookstein, 1989) was used to quantify cranial shape differences among specimens and the consensus configurations. The relative warps method (RW) was employed to compare the configurations of landmarks and semilandmarks (Bookstein, 1991; Rohlf, 1993). The RWs are principal component vectors of the partial warps, which are variables generated for thin-plate spline transformations (Bookstein, 1989), plus component uniform vectors (Rohlf and Bookstein, 2003). These were used to describe the major trends in shape variation among specimens within the sample and between the consensus configurations of deformed and nondeformed samples (for a review on this subject see Rohlf, 1993, 1996). The RWs analyses were performed by

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Fig. 4. Deformation grids representing the variation along the first relative warps axis for male (a and b) and female (c and d) Chubut River Valley samples.

means of the tpsRelw 1.44 software (Rohlf, 2006). An important aspect of these analyses is that one can express the results of the statistical analysis as a deformation of each case over the mean form or reference (Bookstein, 1989, 1991; Rohlf, 1993, 1996). The alpha parameter was used with a zero value, including all scales of variation (Rohlf, 1993, 1996). To establish the relationship between cranial deformation and the presence of nonmetric traits within a sample (objective a), the first RW (in an Euclidean space) calculated from the individuals of Negro and Chubut River Valley samples was compared with the first principal coordinate (PCO; Gower, 1971) based on the Manhattan distance computed on different set of nonmetric traits (by regions and by origin; see Table 2). A Pearson correlation analysis with permutations (10,000) was used to find the association between them (Digby and Kempton, 1987). Finally, the influence of cranial deformation on the evolutionary relatedness among the studied samples based on nonmetric traits (objective b) was evaluated by using Euclidean distances (Sokal, 1961) calculated over the frequency of different set of traits (by regions; see Table 2). The Euclidean matrices were then employed to perform a principal coordinate analysis (Gower, 1971) which allows us to acquire the genealogical pattern among samples. Although other distances are used in nonmetric traits analysis (e.g. sMMD, see Sjøvold, 1973) they result in a similar cluster pattern (Gonza´lez Jose´ et al., 2001). As RW and PCO—both in an Euclidean space—are often used as an exploratory analysis of the variation patterns in a data set, we used Procrustes analysis to compare the ordination patterns produced by morphometric and nonmetric traits data (i.e. frequency), for deformed and

nondeformed samples (Gower, 1971; Digby and Kempton, 1987; Peres-Neto and Jackson, 2001). The two-dimensional ordinations were scaled and rotated to find an optimal superimposition to maximize fit (Gower, 1971). The sum of the squared residuals between configurations in their optimal superimposition can be then used as a measure of association (m12; Gower, 1971). A permutation procedure (PROTEST) implemented by Jackson (1995) was used afterwards to assess the statistical significance of the Procrustean fit (Permutation 5 10,000; Peres-Neto and Jackson, 2001). Procrustes analysis was made using Vegan 1.4.4 package for R 1.9.1 (Ihaka and Gentleman, 1996).

RESULTS The shape variation within the groups of nondeformed individuals and all individuals (deformed and nondeformed) showed important differences for females and males from Negro River Valley, while differences were not found on samples from Chubut River Valley (Table 3). Similar results were observed in the variation of the proportion of nonmetric traits (Table 3). The effect however is less important that in metric traits. The results for the RW analysis of the cranial vault in lateral norm for Chubut River Valley are graphed in Figures 3 and 4. The Figure 3a shows the two first RW scores for Chubut River Valley male sample, where a continuous distribution of cranial vault morphologies around the mean shape is observed. The Figure 3b, on the other hand, shows the two first RW scores for Chubut River Valley female sample, where two little differentiated groups along the first RW can be observed (the dividing point for the two groups can be established at

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Results of correlation analysis performed over the first RW of cranial vault shape and the first PCO of nonmetric traits are shown in Table 4. The association between the first axis of metric and nonmetric traits is high for cranial vault and wormian bones in Negro River sample. The Chubut River Valley sample (Table 4) does not shown significant association. On Table 5 nonmetric traits’ frequency for these two samples is shown. The anteriorly placed wormian bones of Negro River Valley sample have a zero frequency. Finally, Figure 7 show the ordination (principal coordinate scores) calculated from the Euclidean distance obtained for nondeformed (Fig. 7a) and deformed (Fig. 7b) male and female samples. The visual comparison of these ordinations shows that the relative distances between samples are similar for nondeformed and deformed samples (Fig. 7), and the Procrustes analysis (Table 6) establishes that this is a significant similarity. On the contrary, the Procrustes comparison of these ordinations with the PCO calculated for the cranial vault (principally wormians bones) on deformed and nondeformed individuals, does not show any significant similarity (Table 6). When the cranial vault traits are excluded from the analysis, the ordinations do no differ from the PCO calculated with all traits (Table 6). The Procrustes analyses made with RW and PCO did not display significant associations (and therefore the results are not shown).

DISCUSSION

Fig. 5. Relative warps analysis of lateral norm for the male (a) and female (b) Negro River Valley samples.

the 0 score of the RW1). Figure 4 displays the deformation grids for the negative and positive values of score 1 for males (Fig. 4a,b) and females (Fig. 4c,d), with variations concentrated on different areas of the outline. The grids corresponding to the positive value of score 1 for male individuals (Fig. 4b), and the negative value for female individuals (Fig. 4c) presents a slight compression on the lambda region. The results of the RWs analysis of the cranial vault in lateral norm for Negro River Valley are graphed in Figures 5 and 6. The Figure 5a,b shows the two first RW scores for Negro River Valley male and female samples, respectively, where two clearly differentiated groups along first RW can be observed. Figure 6 display the deformation grids for negative and positive values of score 1 for males (Fig. 6a,b) and females (Fig. 6c,d). The score 1 gids for positive values of male and female individuals (Fig. 6b,d) present variations concentrated on both occipital and frontal regions, as well as an expansion in the posterior area of parietal bones.

Traditionally, analyses of artificial cranial vault deformation were performed using discrete categories (i.e. presence–absence). However, to analyze it by means of geometric morphometrics methods allowed us to consider the totality of the cranial variation related to artificial deformation in a continuous manner, granting a new boarding of the relationship between deformation and cranial nonmetric traits expression. Our results indicate that, in some samples, artificial cranial vault deformations alter the variation and covariation of metric and nonmetric traits. Wormian bones of Negro River Valley sample in particular, placed on the cranial vault sutures, are the most influenced by this factor. The Chubut River Valley sample is the only one where the influence of artificial cranial vault deformation is not clear for nonmetric traits (Table 4). Moreover, the samples of Chubut and Negro River Valleys differ in two aspects. First of all, the artificial deformation presents different characteristics, with the Chubut River Valley sample showing a slight compression in the lambda region, while in the Negro River Valley we found both occipital and frontal regions as being the most influenced, plus an expansion in the posterior area of parietal bones. Second of all, the two samples differ on the nonmetric traits expression, in particular for the Negro River Valley samples, presenting a 0 frequency for some anteriorly placed wormians bones (Table 5). This suggests, in concordance with previous analyses (Pucciarelli, 1974) that the presence of nonmetric traits is independent from deformation, while its frequency does covary with it. This implies also that concerning the degree of cranial deformation influence over the frequency of nonmetric traits, the more marked the artificial cranial deformation is, the larger the influence will be (e.g. Negro River Valley; Table 3 and Figures 5 and 6).

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Fig. 6. Deformation grids representing the variation along the first relative warps axis for male (a and b) and female (c and d) Negro River Valley samples. TABLE 4. Correlations between the RW1 (shape axis) and the different PCO1 (nonmetric axis) calculated by region and origin Region

Origin

Samples

All traits

Cranial vault

Face

Base

Wormians

Vessel and nerve

Hypostotic and hyperostotic

NR female NR male ChR female ChR male

0.145 0.046 0.236 0.071

0.167 0.356* 0.087 0.021

0.087 0.040 0.169 0.131

0.035 0.254 0.286 0.023

0.165 0.340* 0.087 0.021

0.095 0.107 0.206 0.102

0.005 0.179 0.053 0.058

* P  0.05.

A consensus regarding the level of influence that artificial cranial vault deformation has over nonmetric trait frequencies among human populations has not been reached in previous works. Nearly a hundred years ago, Dorsey (1897) suggested that the high relative frequency of coronal ossicles in a sample of Kwakiutl crania was caused by the annular deformation practiced by this group. In contrast, Sullivan (1922) was not able to find a clear association between deformation and discrete trait frequencies for North American samples. A drawback for most of these studies is that they did not compare nonmetric trait frequencies between deformed crania within individual populations, and consequently it was impossible to tell whether trait frequency differences were due to deformation or to simple variation between populations (Konigsberg et al., 1993). More recently, Corruccini (1976), Cheverud et al. (1979), and Richtsmeier et al. (1984) have documented the interdependency of nonmetric and metric variation in the human crania. They pro-

posed that there are environmental correlations among morphological aspects of the crania and it is possible that deformation could act jointly over both nonmetric and metric variation, at least at a local level within the crania. In the same way, a major agreement has been reached over the fact that artificial cranial deformation modifies the expression of vault wormian bones (Ossemberg, 1970; Sjøvold, 1973; Pucciarelli, 1974; Konigsberg et al., 1993; White, 1996; O’Loughlin, 2004). The wormian bones are located on the fontanelles or ‘‘temporarily unossified area’’ of the cranial vault (Bregmatic bone in anterior fontanelle; Lambdoid ossicle in posterior fontanelle; Epipteric bone in anterolateral fontanelle; Asterionic bone in posterlateral fontanelle; and Sagittal ossicle in fetal sagittal fontanelle) (Pucciarelli, 1974; Barnes, 1994), and they end its development during postnatal life, when these fontanelles are ossified. According to Ossemberg (1970) artificial and pathological deformation

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TABLE 5. Frequency of nonmetric traits in negro and Chubut River Valley Nonmetric cranial traits name MT EB CO SO AB LO AsB PNB MF IB FOI FSI CC DHC PsBS PaBS MTo IS FSM MIF NSM TS

Region Cranial Cranial Cranial Cranial Cranial Cranial Cranial Cranial Cranial Cranial Base Base Base Base Base Base Face Face Face Face Face Face

vault vault vault vault vault vault vault vault vault vault

Origin

NR Female

NR Male

ChR Female

ChR Male

Hypostotic Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Hypostotic/wormian Vessel and nerve – Hypostotic Hypostotic Vessel and nerve Hyperostotic Hyperostotic Hyperostotic Hyperostotic Hypostotic Vessel and nerve Vessel and nerve Vessel and nerve Hyperostotic

0 0 0 0 0 34 11 3 94 3 9 29 71 29 31 69 3 26 49 31 91 3

0 0 3 0 9 23 6 6 97 3 3 20 71 34 51 60 3 17 49 46 89 14

0 14 0 3 7 28 21 7 100 0 7 14 79 34 21 90 24 69 76 28 83 14

0 7 2 2 2 37 5 7 100 9 0 7 72 40 81 81 16 51 81 35 93 0

disturbs the formation of ossicles in the sutures. O’Loughlin (2004) also indicates that all kinds of cranial deformation (whether cultural or as the result of craniosynostosis) affect the frequency of certain types of wormians bones. Therefore, artificial deformation is a source of suture ossification retard and stimulates the formation of accidental ossification centers in the persisting membranous tissue, increasing the formation of neurocranial wormians bones (Ossemberg, 1970; Pucciarelli, 1974; Barnes, 1994). In this sense, Konigsberg et al. (1993) have pointed out that the traits whose development is known to occur specifically in the fetal period are unaffected by deformation, whereas this affect nonmetric traits frequencies that finish its development during postnatal life and that are near areas of maximum growth alteration (as some cranial vault ossicles). Likewise, other nonmetric traits like basicranial vessels and nerves, which are formed more rapidly during embryonic and fetal life and derive from the chondrocranium (Lieberman et al., 2000a,b; Sperber, 2001), will be less affected by the artificial cranial vault deformation in postnatal life. In another way, Konigsberg et al. (1993) suggests that, although artificial cranial vault deformation can influence the relative frequency pattern of a few nonmetric cranial traits, these effects are minimal and the influence over the resulting evolutionary relationships of human populations is insignificant. The results from this study partially support Konigsberg et al. (1993) suggestion, showing that the artificial cranial vault deformation did not highly influence the pattern of nonmetric traits variation between samples. However, the wormians bones are affected by the artificial deformation in samples with a strong cranial deformation (i.e. the Negro River Valley sample). The use of these traits in the analyses of evolutionary relationships disguises some relatedness (Table 6). The exclusion of these traits, or its use together with numerous other traits, permits to obtain results that are in agreement with spatial variation of the studied samples. The patterns obtained in these analyses agree with the spatial variation observed in the area, particularly for the San Juan and Calchaqui Valley sam-

Fig. 7. Principal coordinate analysis scores calculated in base to the Euclidean distance obtained for nondeformed (a) and deformed (b) male and female samples.

ples, which are spatially separated from the other samples analyzed (located in Patagonia). Likewise, these results are in global agreement with craniofacial morphometric analyses previously made in the area (Perez, 2006).

CONCLUSION The most affected nonmetric traits are those that develop during the postnatal period and are near areas of maximum growth alteration by deformation. Wormians bones are particularly influenced by environment (e.g.

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TABLE 6. Association (m12) between PCO ordinations for the analyzed samples, calculated over cranial vault, and face-cranial base traits from deformed (D) and nondeformed (ND) individuals D all traits

ND all traits

D cranial vault

ND cranial vault

D face and base

ND face and base

1 0.88* 0.73 0.76 0.93* 0.83**

1 0.56 0.62 0.78 0.98*

1 0.68 0.60 0.50

1 0.63 0.47

1 0.75

1

D all traits ND all traits D cranial vault ND cranial vault D face and base ND face and base * P  0.01, ** P  0.05.

cranial deformation practices) during the postnatal development and therefore they are not relevant in evolutionary relationships analysis. This supports the importance of carefully considering traits choice when performing evolutionary relationship studies, and most of all their relative constancy of expression under variable environmental conditions (Deol and Truslove, 1957; Berry, 1963; Ossemberg, 1970). It is remarkable that the evolutionary relationships established in base to the frequency of nonmetric traits can be more affected in geographic areas where populations practiced a marked artificial cranial deformation (e.g. Bolivian altiplano).

ACKNOWLEDGMENTS We are grateful to Hector M. Pucciarelli [Divisio´n Antropologı´a. Facultad de Ciencias Naturales y Museo of La Plata (Argentina)], Rafael Gon˜i, and to Ine´s Baffi and Leandro Luna [Museo Etnogra´fico ‘‘J. B. Ambrosetti’’ of Buenos Aires (Argentina)] for granting access to the human skeletal collection under their care. We thank Valeria Bernal, Paula Gonzalez, Leandro Monteiro and two anonymous reviewers for provide helpful comments. We also thank to Amelia Barreiro for helping with the English version of the manuscript. The drawings were created by Marina Perez.

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