effects of different kinds of cranial deformation on theincidence of wormian bones.pdf

8/12/2019 Effects of Different Kinds of Cranial Deformation on theIncidence of Wormian Bones.pdf

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Effects of Different Kinds of Cranial Deformation on the

Incidence of Wormian Bones

Valerie Dean OLoughlin*

Medical Sciences Program, Indiana University, Bloomington, Indiana 47405

KEY WORDS cultural deformation; ossicles; supernumerary bone; sutural bone;craniosynostosis

ABSTRACT Researchers have debated whether thepresence and frequency of wormian bones (sutural bones,supernumerary bones, and ossicles) are attributable togenetic factors, environmental factors, or both. This re-search examines the effects of many different kinds ofcranial deformation on the incidence of wormian bones. A

sample of 127 deformed and undeformed crania from NewWorld archaeological sites was examined. An undeformedcranial sample (n 35) was compared to the followingcranially deformed groups: 1) occipital, 2) lambdoid, 3)annular, 4) fronto-vertico-occipital, 5) parallelo-fronto-oc-cipital, and 6) sagittal synostosis. Three levels of degree ofcultural cranial deformation were qualitatively deter-mined. Type and number of wormian bones along eachmajor suture were recorded for each cranium. Groupmeans were analyzed using Kruskal-Wallis one-way

ANOVA statistical tests to test the null hypothesis thatcranial deformation does not have an effect on wormianbone incidence. Results indicate that all forms of cranialdeformation affect the frequency of some types of wormianbones. In particular, all cranially deformed groups exhib-ited significantly greater frequencies of lambdoid ossicles.

Apical, parieto-mastoid, and occipito-mastoid wormianbones also appeared with greater frequency in somegroups of culturally deformed crania. Further, varyingdegrees of cultural deformation all had more lambdoidwormian bones than the undeformed group. These resultssuggest that wormian bone development in posteriorlyplaced sutures may be affected more by environmentalforces than are their anteriorly placed counterparts. Am JPhys Anthropol 123:146155, 2004. 2004 Wiley-Liss, Inc.

Wormian bones (sutural bones, supernumerarybones, and ossicles) are irregularly shaped bonesformed from independent ossification centers foundalong cranial suture lines and fontanelles (Hauserand De Stefano, 1989). Dorsey (1897) was among thefirst to suggest that pressure on the cranium fromcultural cranial deformation may influence the inci-dence of wormian bones. Many researchers exam-ined this question and presented hypotheses con-cerning wormian bone etiology. The first is that theformation and incidence of wormian bones are pri-marily under genetic influence, and external factorssuch as cultural cranial deformation do not play amajor role in wormian bone formation (Berry andBerry, 1967; Finkel, 1976). Berry and Berry (1967)

examined the presence (but not frequency) ofwormian bones in several skeletal populations. Theysuggested that the presence of wormian bones wasgenetically influenced and had minimal epigeneticinfluence. Finkel (1976) even suggested thatwormian bone formation was the result of a singlegene.

A second hypothesis maintains that environmen-tal stressors (e.g., cultural cranial deformation orexperimentally created craniosynostosis) affect theincidence of wormian bones (e.g., Dorsey, 1897; Os-senberg, 1970). Schultz (1923) postulated that theformation of bregmatic bones is due to delayed clo-

sure of the anterior fontanelle. Pucciarelli (1974)stated that experimental immobilization of rat cra-nia could positively affect the frequency of wormianbones. Bennett (1965) examined Euro-American,Black, and Native American crania for the presenceof lambdoid wormian bones, and hypothesized thatthese bones were the result of a stressor along thelambdoid suture. White (1996) found that fronto-occipital modification was positively associated withthe presence of lambdoid ossicles.

Craniosynostosis is the premature fusion of one ormore of the calvarial sutures (Bixler and Ward,1987). Craniosynostosis may be considered an envi-ronmental stressor if, by altering skull-growth vec-tors, it affects the presence and frequency of

wormian bones. Burrows et al. (1997) examined the

Preliminary findings were presented at the 69th Annual Meeting ofthe American Association of Physical Anthropologists.

*Correspondence to: Valerie OLoughlin, Medical Sciences Pro-gram, Jordan Hall 104, Indiana University, Bloomington, IN 47405.E-mail: [email protected]

Received 9 April 2001; accepted 28 February 2003.

DOI 10.1002/ajpa.10304Published online 10 June 2003 in Wiley InterScience (www.

interscience.wiley.com).

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 123:146155 (2004)

2004 WILEY-LISS, INC.


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frequency of coronal and sagittal wormian bones inrabbits which had either delayed onset or experi-mentally created coronal suture synostosis. Theydiscovered that the experimentally created synos-totic group had wormian bones that appeared after(not prior to) the onset of cranial growth alteration,

suggesting wormian bone formation was affected byexternal factors.A third hypothesis states that while the presence

of wormian bones may be genetically determined,external factors may influence the number of suchbones (e.g., El-Najjar and Dawson, 1977; Gottlieb,1978; Anton et al., 1992). El-Najjar and Dawson(1977) stated that the presence of lambdoid wormianbones is under strong genetic control, but the num-ber of wormian bones can be influenced by culturalcranial deformation. Gottlieb (1978) discovered thatcultural cranial deformation had a direct effect onincreased sutural complexity in the lambdoid su-ture, and an indirect effect on increased numbers of

lambdoid wormian bones. Anton et al. (1992) notedthat undeformed crania displayed more ossiclesthan circumferentially deformed crania, but the un-deformed group had fewer ossicles than anteropos-teriorly deformed crania. Anton et al. (1992) hypoth-esized that since circumferential deformation willplace compressional forces on the sutures, this com-pression will result in fewer sutural bones. In con-trast, anteroposterior deformation places tension(not compression) on the lateral aspect of the cra-nium, and the increase in tension at the sutures mayresult in an increase of sutural bones.

Previous studies typically examined only a fewkinds of cultural cranial deformation (e.g., El-Najjarand Dawson, 1977; Anton et al., 1992) or examinedeffects of craniosynostosis only on sutural bone fre-quency (Burrows et al., 1997). Other studiesgrouped different types and degrees of cultural de-formation together (El-Najjar and Dawson, 1977),without examining the possible effects these vari-ables could have on the incidence of wormian bones.Some studies only examined the presence ofwormian bones along a single suture (e.g., Berry andBerry, 1967; White, 1996), without studying the fre-quency of these ossicles.

The present study examines the effects of manydifferent kinds and degrees of cranial deformation

on the incidence of different kinds of wormian bones.The cranially deformed groups include both cultur-ally modified crania and a craniosynostosis sample.Comparisons are made among culturally deformed,craniosynostotic, and undeformed groups in an at-tempt to reach a better understanding of wormianbone development. The research hypothesis is thatcranially deformed and craniosynostotic groups willhave different frequencies of wormian bones com-pared to an undeformed group. In particular, it ishypothesized that cranial deformation and cranio-synostosis will positively influence the numbers of atleast some kinds of wormian bones. Before results

are presented, a brief ethnographic survey of cul-tural cranial deformation is warranted.

ETHNOGRAPHIC INTRODUCTION TO

CULTURAL CRANIAL DEFORMATION

The term cultural cranial deformation is used to

describe practices that alter the shape of the cra-nium in infancy and early childhood. Since the cra-nium is malleable in the first years of life (Dean,1995a), it is easy to modify head shape. Evidence ofcultural cranial deformation has existed worldwidefor several thousand years (Dingwall, 1931; Dean,1995a). Most cultural deformational procedures be-gin within the first few days of life, and the deform-ing apparatus is used for approximately 6 months to1 year. Populations in Ecuador and Peru sometimesused the deforming apparatus for as long as 35years (Dingwall, 1931; Topinard, 1879). Both maleand female children had their skull shape modified.

Cultural cranial deformation could be intention-

ally induced in a variety of ways (Dingwall, 1931;Dean, 1995a). The vault could be tightly encircled bybandages, producing a cylindrical or conical headshape (e.g., in South America). Securing the skullbetween two boards flattened those portions of thehead in direct contact with the boards (e.g., on theNorthwest Coast of North America). In some cul-tures, the deformation may have been uninten-tional, as when an infant was secured on a cradle-board for a long period of time, consequentlyflattening the back of the head (e.g., the SouthwestUS).

Reasons for modifying cranium shape were variedand sometimes culture-specific (Dingwall, 1931;Topinard, 1879; Dean, 1995a). Northwest Coast, Co-lumbian, and Peruvian cultures viewed males whohad deformed skulls as more brave and powerful.Most cultures that practiced intentional moldingviewed a molded head as a sign of high status.Often, slaves were not allowed to practice culturalcranial deformation, and so their head shape was aphysical sign of their social status (e.g., NorthwestCoast). In addition, culturally modified skulls wereviewed as a sign of beauty, and the more marked thedeformation, the more beautiful the person was re-garded as being.

It is common to see ranges of cranial deforma-tion within and among cultures. Some individualsmay have had slight cranial deformation, whereasothers had more marked deformation. The length oftime the deforming apparatus was used, how tightlythe apparatus fit, and the reasons for modifyingskull shape created these ranges of deformation(Dingwall, 1931; Dean, 1995a). Cranial deformationresearch must not ignore these ranges, and incorpo-rate them into the research design where possible.

MATERIALS AND METHODS

One hundred twenty-seven adult crania from theNational Museum of Natural History, the Thomas

CRANIAL DEFORMATION AND WORMIAN BONES 147


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Gilcrease Institute of American History and Art(Tulsa, OK), and the Indiana University collections,representing many geographically distinct NewWorld archaeological populations, were analyzed. Alist of deformational groups, geographic locationsand archaeological sites of crania, and cultural/tem-

poral information is given in Table 1. Those craniawith provenience information were historic, or dat-ing from no later than the 1800s. There was limitedprovenience information for most crania, but severalfactors (e.g., condition of remains, anecdotal infor-mation) indicated that crania were of more recentorigin. The wide range of populations was selectedbecause: 1) wide sampling maximizes cranial diver-sity and minimizes the risk of unintentionally se-lecting for population-specific traits, and 2) no singlearchaeological population examined contains a suf-ficient number of undeformed, culturally deformed,and craniosynostotic crania. All cranial groups (ex-cept the lambdoid deformed group) contain speci-

mens from multiple, geographically distinct regions.Lamboid deformed specimens came from multiplearchaeological sites but were limited to the South-west US. Detailed ethnographic information aboutthe deformational practices of these regions is inDingwall (1931) and Dean (1995a).

Age was estimated by endocranial and ectocranialsuture closure and dental wear. This study did notneed the exact age of each cranium, but needed anestimate as to whether the cranium belonged to ayounger (1840 years) or older (4055 years) in-dividual. Meindl and Lovejoy (1985) noted that al-though ectocranial suture closure scoring can haveoverlap and variability, this method is still able to

provide a good general age-range estimate. As withsuture closure, dental wear evaluation was usedonly as a relative measure of age, to separateyounger from older individuals. As others noted(Hillson, 2000), dental wear varies considerablyamong populations, and may not be a reliable exactage indicator for crania from different populations.

Younger male individuals (ages 18 40) were se-lected to decrease the possibility of age-related su-ture closure and to avoid overlooking obscuredwormian bones. Ages ranged from 1840 years forall but two craniosynostotic crania (age range,4055 years). Population frequencies of craniosyn-ostosis range from 315 per 10,000 individuals (Co-

hen, 1986b; French et al., 1990), so control on ageand sex in the craniosynostotic group was relaxed tomaximize sample size. As a result, some female cra-nia were included in the undeformed and occipitaldeformed samples for comparative purposes. Berryand Berry (1967) showed that sutural bones appearin equal frequency between the sexes, so the benefitof having a larger craniosynostotic sample size out-weighed the risk of having a mixture of male andfemale crania in three of the samples.

Type and degree of cultural cranial deformationwere qualitatively determined by visual inspection.Deformational types included those described by

Neumann (1942) and Hrdlicka (1910): 1) occipitaldeformation (n 30), 2) lambdoid (n 9), 3) fronto-vertico-occipital (n 13), 4) parallelo-fronto-occipi-tal (n 18), and 5) annular (n 14) (see Fig. 1).Occipital deformation is a vertical flattening of thenuchal portion of the occipital bone. Lambdoid de-

formation is a flattening of the cranium around theregion of lambda. Fronto-vertico-occipital deforma-tion is a vertical flattening of the upper portion ofthe occipital, as well as an oblique flattening of thefrontal bone. Parallelo-fronto-occipital deformationflattens the frontal region and the occipital boneproper. The occipital bone is flattened obliquely,whereby the frontal and occipital bones are approx-imately parallel to each another. Annular deforma-tion compresses the cranium cylindrically, so thatthe cranium becomes ovoid.

Degree of deformation was classified as none,slight, moderate, or marked. No cranial deforma-tion was defined as no evidence of cultural cranial

deformation. Slight deformation was some evi-dence of altered cranium shape, but which couldbe overlooked in more casual observation. Mod-erate deformation was noticeable alteration ofcranium shape. Marked deformation was clearindication of drastically altered cranium shape.Degree was determined by two or more visualinspections by the author, using multiple compar-ative crania from the same area. Detailed methodsof analysis for type and degree of cultural cranialdeformation were previously described (Dean,1995a,b; OLoughlin, 1996).

Isolated (as opposed to syndromic) craniosynosto-ses were selected for, to minimize the possibilitythat a syndrome itself caused the wormian boneincidence, as opposed to the resulting prematuresuture closure. Syndromic craniosynostosis also hasa strong genetic component, whereas isolated cra-niosynostosis may be the result of environmentalfactors, such as in utero constraint (Cohen, 1986a,1988; Bixler and Ward, 1987). Isolated craniosynos-toses were determined by inspecting for prematureendocranial and ectocranial sutural fusion, and not-ing that the crania lacked certain facial anomaliescharacteristic of syndromic craniosynostoses (Cohen1986a, 1988; Bixler and Ward, 1987). All crania (n 7) displayed sagittal synostosis; two crania also had

either lambdoid synostosis or unilateral occipito-mastoid synostosis.An undeformed cranial sample (n 35) from mul-

tiple New World archaeological populations wasused for comparative purposes. These populationswere different from the deformed populations, be-cause according to the ethnographic literature (re-viewed in Dingwall, 1931; Dean, 1995a), culturallymodifying the cranium was a practice often limitedto individuals of higher classes. Thus, undeformedcrania in culturally deformed populations were morelikely to be individuals of a different socioeconomicsetting (and perhaps a different genetic and/or nu-

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TABLE 1. Geographic, site, and cultural affiliation and temporal distribution of cranial samples

Cranial groupGeographic location

(number of individuals) SexArchaeological site(s)

(if known)1Cultural affiliation

(if known)Temporal information

(if known)2

Undeformed (n 35)Montana (5) M Benton City Spokane Historic

M Tongue River Sioux HistoricM Fort Ellis Unknown HistoricM Fort Shaw Unknown HistoricM unknown Unknown Unknown

Kansas (2) M Doniphan site Unknown UnknownM near Fort Harker Kaw Unknown

California (1) M Nicolaus Mound Unknown UnknownOregon (1) M Emigrant Springs Pah Ute UnknownNew Mexico (2) M Fort Wingate Navaho Late 1800s

M Fort McRae Navaho HistoricUtah (1) M Rock Grave Pah Vant UnknownCanada (1) M Fort Good Hope Hare Historic

Arkansas (2) F Unknown Unknown UnknownM Dickson Farm Unknown Unknown

Texas (4) M Columbia Comanche HistoricM P ecos River Comanche HistoricM Fort Concho Comanche HistoricM Fort McKarth Comanche Historic

South Dakota (5) M (3) Swan Creek site Arikara HistoricM (2) Mobridge site Possibly Arikara 1700s1800s

Illinois (7) F Greene County Unknown UnknownF Snyders site Woodland WoodlandM (3) Jersey County Woodland Woodland

M (2) Barry Farm Hopewell HistoricMD (1) M Ossuary 4, Ferguson Farm Mid-Atlantic seaboard HistoricUnknown location (3) F Unknown Arikara Unknown

F Unknown Chickasaw UnknownM Unknown Unknown Unknown

Occipital deformation(n 30)

Peru (18) M (15) Pachacamac Pachacamac 01500 ADM Chilca Unknown UnknownM (2) Near fortress of Paramonga Unknown Middle/Late period

New Mexico (5) M (2) Guisiwa, Jemez Valley Pueblo 17th centuryM Puye Tewa UnknownM Hawikuh Zuni UnknownM Pueblo Bonito Zuni Unknown

Arizona (4) F Unknown Unknown UnknownM (2) McDonalds Canyon Ancient Pueblo UnknownM Crescent Cliff Ancient Pueblo Unknown

Arkansas (2) F Unknown Unknown UnknownF Unknown Arikara (possibly) Unknown

Northwest Coast (1) F Shell Mound Unknown Unknown

Lambdoid deformation(n 9)New Mexico (6) M Pajarito plateau Tewa Unknown

M Kwasteyukwa Pueblo UnknownM (2) Hawikuh Pueblo Zuni UnknownM (2) Pueblo Bonito Ruin Pueblo Unknown

Arizona (2) M Canyon del Muerto Navaho UnknownM Near Allantown Pueblo Unknown

Utah (1) M Alkali Ridge Unknown UnknownFronto-vertico-occipital

(n 13)Washington (6) M (2) Neah Bay Makah Historic

M (3) Ft. Townsend Cowichan HistoricM Vantage Ferry Unknown Unknown

Peru (6) M Lima Unknown UnknownM (3) Pachacamac Pachacamac 01500 ADM (2) Chicama Unknown Unknown

Bolivia (1) M Cachilaya Unknown UnknownParallelo-fronto-occipital

(n 18)Washington (5) M Pacific Country Salish Historic

M (2) Puget Sound Nisqually HistoricM (2) Pacific Country, Columbia River Chinook Historic

Oregon (4) M (2) Unknown Chinook HistoricM (2) Memaloose Island Unknown Historic

Arkansas (1) M Newport Unknown HistoricPeru (4) M (2) Lima Unknown Unknown

M Candivilla Unknown UnknownM Pachacamac Pachacamac 01500 AD

Dominican Republic (3) M (3) Countanza Arawak HistoricVenezuela (1) M Lake Tacarigua Unknown Unknown

(Continued)



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tritional setting) than culturally deformed individu-als.

Number and placement of wormian bones weredetermined by visual inspection. Only those boneswhich were clearly visible were counted. Wormianbones were grouped according to the suture or junc-tion of sutures where they were found (Figs. 2, 3): 1)coronal, 2) pterionic, 3) sagittal, 4) apical (junction ofsagittal and lambdoid sutures), 5) lambdoid, 6) as-terionic (junction of lambdoid, parieto-mastoid, andoccipio-mastoid sutures), 7) parieto-mastoid, 8) oc-cipito-mastoid, 9) squamosal, and 10) parietal notch(junction of the parieto-mastoid and squamosal su-

tures). (No bregmatic bones were found in this sam-ple.) Inca bones were excluded from this analysis,because their development and occurrence appear tobe the result of nonfusion of the squamous part ofthe occipital to the other components of the occipital,and are under great genetic influence (Hauser andDe Stefano, 1989).

Statistical analysis was performed using SPSS forWindows, release 10.0.0 (SPSS, Inc., 1999). Kruskal-Wallis one-way ANOVA tests were used to analyzewormian bone group means, since most ossicle fre-quency ranges were small (ranges typically werefrom 03). Kruskal-Wallis ANOVA is a nonparamet-ric test that determines a mean rank for each

group. A higher mean rank is indicative of a higherfrequency of wormian bones in a particular group.Probability values ofP 0.05 were considered sta-tistically significant. Undeformed crania were com-pared to both culturally deformed and craniosynos-totic crania, to determine if there were differences inthe number of wormian bones among the groups.Next, culturally deformed crania were regroupedaccording to posterior degree of deformation. Unde-formed crania then were compared to the differentdegree groups to determine if the degree of deforma-tion affected the number and placement of wormianbones.

RESULTS

Table 2 lists mean number of wormian bones percranial group. Means were rounded to the closestwhole number. Ranges were largest for coronalwormian bones (ranges of 0 11 wormian bones) andlambdoid wormian bones (ranges of 022). All cra-nially deformed groups exhibited higher mean num-bers of lambdoid wormian bones than the unde-formed group.

Table 3 lists Kruskal-Wallis ANOVA results com-paring number of wormian bones among each cra-nial group. One of the craniosynostotic specimens

(no. 276981) was eliminated from the lambdoidwormian bone analysis because the cranium had alambdoid synostosis as well, reducing the craniosyn-ostotic sample to 6. Since the craniosynostotic spec-imens had sagittal synostosis, this group was notused for the sagittal wormian bone analysis. Signif-icant results were obtained for lambdoid wormianbones and occipito-mastoid wormian bones (Table 3).All cranially deformed groups had significantlyhigher mean ranks for lambdoid wormian bones(and thus, a higher frequency of these bones) thanthe undeformed group. Two cranially deformedgroups (parallelo-fronto-occipital and annular) ex-hibited lower mean ranks for occipito-mastoid os-

sicles than the undeformed group, and the remain-ing groups had higher occipito-mastoid mean ranksthan the undeformed group. Culturally deformedcrania also had higher frequencies of apical bonesthan the undeformed group. Table 3 also shows thatthe craniosynostotic group had much higher meanranks for pterionic, lambdoid, occipito-mastoid, andsquamosal bones than the undeformed group. Incontrast, the undeformed group had higher frequen-cies of coronal wormian bones.

Lambdoid and occipital deformed groups weresimilar in that both had slightly greater frequenciesof coronal and apical ossicles, and much greater

TABLE 1. (Continued)

Cranial groupGeographic location

(number of individuals) SexArchaeological site(s)

(if known)1Cultural affiliation

(if known)Temporal information

(if known)2

Annular (n 14)Chile (1) M Aricara Unknown UnknownBolivia (3) M Lake Titicaca Aymara Unknown

M Sicasica Unknown UnknownM Cachilaya Unknown Unknown

Peru (10) M Coyungo Unknown UnknownM (8) Santa Lucia Unknown UnknownM Cabeza Larga cemetery Paracas Historic

Craniosynostosis (n 7)California (1) M Ponce Mound Unknown UnknownPeru (3) F San Damian Unknown Historic (estimate)

M Cincos Cerros Unknown Historic (estimate)M Cincos Cerros Unknown Historic (estimate)

Arkansas (1) M Drew County Unknown UnknownMaryland (1) M Ossuary #4, Accokeek Middle Atlantic seaboard Historic

Alaska (1) F Nunivak Island Eskimo Historic

1 Provenience information was limited for most of these crania. Most information included just general locality, skeletal remainsrecovered, and whether remains were Native American.2 While exact dates are not known for most specimens, other information (e.g., condition of crania, history about process of obtainingthese skeletal collections) indicate that crania are not ancient, but rather are from more recent populations.

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frequencies of lambdoid ossicles than the unde-formed group. The parallelo-fronto-occipital and an-nular deformed groups had greater frequencies ofcoronal, pterionic, apical, squamosal, and lambdoidossicles than the undeformed group. In contrast, thefronto-vertico-occipital group had lower frequenciesof coronal and pterionic wormian bones, but much

higher frequencies of almost all of the posteriorly-placed wormian bones.

Culturally deformed crania were resorted intosimple deformed (i.e., occipital and lambdoid de-formed) or complex deformed (i.e., fronto-vertico-oc-cipital, parallelo-fronto-occpital, and annular)groups for further analysis. Table 4 shows Kruskal-

Fig. 1. Cranial types used in this analysis. Crania shown are from National Museum of Natural History (Smithsonian Institution,Washington, DC).



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Wallis ANOVA results comparing the number ofwormian bones among the undeformed, simple de-formed, and complex deformed groups. Both de-formed groups had higher frequencies of apical andlambdoid wormian bones than the undeformedgroup. Crania in the simple deformed group had astatistically signifcant higher mean rank of sagittalwormian bones than the undeformed or complexdeformed groups. Since lambdoid deformed crania

(which make up part of the simple deformed group)came from one general region, this may play a role inthese findings.

Table 5 shows Kruskal-Wallis ANOVA resultscomparing posterior degree of cultural deformationwith number of wormian bones. Here, undeformed

and culturally deformed crania were regrouped ac-cording to the degree ofposterior cranial flattening(undeformed crania were recoded as none for pos-terior degree of deformation). All deformed groupshad greater frequencies of apical wormian bones,while slight posterior flattening also was associatedwith greater numbers of parieto-mastoid wormianbones. Slight, moderate, and marked deformed cra-nia had statistically significant higher frequencies oflambdoid wormian bones than their undeformedcounterparts.

DISCUSSION AND CONCLUSIONS

These results indicate that all kinds of cranialdeformation (whether cultural or the result of cra-niosynostosis) affect the frequency of certain types ofwormian bones. Wormian bone frequency may in-crease or decrease, depending on the type and de-gree of cranial deformation. All cranially deformedgroups had significantly greater frequencies oflambdoid ossicles, paralleling the results of Sullivan(1922). Apical and parieto-mastoid wormian boneshad greater frequencies in almost all deformedgroups, although these findings were not statisti-cally significant. Note that the lambdoid, apical, andparieto-mastoid wormian bones are in posteriorlyplaced cranial sutures. Anteriorly placed wormian

bone frequencies were more similar between unde-formed and deformed samples. In fact, two groups(fronto-vertico-occipital and craniosynostosis) hadfeweranteriorly-placed wormian bones than the un-deformed group.

Human wormian bone development appears to bedependent on the location of the ossicle. I hypothe-size that wormian bones in more posteriorly placedsutures may be affected more by environmental fac-tors than their anteriorly placed counterparts. Like-wise, wormian bones in the anterior sutures appearto be under stronger genetic control. If this hypoth-esis is correct, it is not surprising that studies onwormian bone incidence have yielded conflicting re-

sults.Why would posteriorly placed wormian bones be

more influenced by environmental factors? One pos-sibility is posteriorly placed wormian bones areformed as a result of posteriorly placed pressurefrom the cultural deforming apparatus. However,this explanation does not explain why crania withsagittal synostosis also have increased numbers ofposteriorly placed wormian bones. Further, Anton etal. (1992) noted that the constriction the deformingapparatus places on a particular suture tends todecrease the number of sutural bones in that samesuture.

Fig. 2. Lateral view of a cranium, illustrating kinds ofwormian bones examined in this study: 1, coronal; 2, pterionic; 3,sagittal; 4, apical; 5, lambdoid; 6, asterionic; 7, parieto-mastoid; 8,occipito-mastoid; 9, squamosal; 10, parietal notch.

Fig. 3. Posterior view of a lambdoid deformed cranium withmultiple wormian bones: 3, sagittal wormian bone; 4, apical

wormian bone; 5, lambdoid wormian bone; 6, asterionic wormianbone.

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Another possibility relates to human brain andcranium development. Moss (1958) noted that theoccipital portion of the brain grows most rapidlyafter birth and positively affects the postnatalgrowth of the posterior part of the cranium. Thisfinding suggests that the posterior cranium couldbe influenced more by external (epigenetic) factorsthan the anterior cranium. Trinkaus and LeMay(1982) suggested that this posteriorly directed

growth of the brain and cranium places greaterintracranial pressure on the lambdoid suture.Greater pressure would create increased tensionalong the suture. How would this affect the cra-niosynostotic group, where the greatest compres-sion is along the fused sagittal suture? Moss(1959) stated that sagittal synostosis redirects thegrowth vectors of the neurocranium in a moreanterior-posterior fashion. The end result could be

TABLE 2. Mean number of wormian bones for each cranial group1

Cranial group

Mean number of Wormian bones

C oron al Pte rion ic Sagit tal A pical Lambdoid A st erio nic Parie to -masto id Occipit o-mast oid Squ amosalParietal

notch

Undeformed (n 35) 1 (011) 0 (02) 0 (0) 0 (01) 3 (010) 1 (02) 0 (02) 0 (02) 0 (01) 0 (02)Occipital (n 30) 3 (010) 0 (02) 0 (04) 0 (01) 6 (016) 1 (02) 0 (02) 1 (05) 0 (03) 0 (02)Lambdoid (n 9) 2 (010) 0 (01) 0 (01) 1 (01) 7 (111) 0 (01) 1 (06) 1 (02) 0 (02) 0 (01)Fronto-vertico-occipital

(n 13)

1 (07) 0 (01) 0 (0) 0 (01) 7 (022) 1 (02) 0 (01) 1 (03) 0 (01) 0 (01)

Parallelo-fronto-occipital(n 18)

2 (09) 0 (02) 0 (0) 0 (01) 6 (020) 1 (02) 0 (01) 0 (01) 1 (012) 1 (02)

Annular (n 14) 2 (06) 0 (01) 0 (0) 0 (01) 4 (012) 0 (02) 0 (03) 0 (0) 0 (02) 1 (02)Craniosynostosis (n 7) 0 (03) 1 (02) 0 (01) 6 (014)2 1 (02) 0 (01) 1 (02) 1 (04) 1 (02)

1 Wormian bone means were rounded to closest whole number. Ranges for each sample are included in parentheses.2 The only craniosynostotic specimen that did not have lambdoid ossicles was that which had lambdoid synostosis (number 276981).

TABLE 3. Kruskal-Wallis ANOVA results comparing cranial group with number of wormian bones1

Wormian bonetype

Mean rank values for cranial group ANOVA values

Undeformed Occipital Lambdoid F-V-O2 P-F-O3 Annular CraniosynostosisChi-square

statistic P-value

Coronal 59.4 72.8 64.9 52.1 66.7 66.5 49.36 6.85 0.335Pterionic 60.1 59.3 59.6 57.6 71.2 74.3 73.0 8.69 0.192Sagittal 58.5 62.5 65.0 58.5 58.5 58.5 6.75 0.240

Apical 57.4 64.0 78.0 72.1 64.0 65.5 52.0 5.86 0.439Lambdoid4 46.8 71.4 83.2 66.3 66.6 56.8 81.94 13.93 0.030*Asterionic 61.5 71.7 41.2 69.0 73.2 50.4 58.1 10.55 0.103Parieto-mastoid 59.9 62.2 72.3 72.0 61.4 62.8 66.6 7.45 0.281Occipito-mastoid 60.4 65.1 77.7 82.0 54.2 48.0 74.1 16.33 0.012*Squamosal 59.7 62.2 65.1 62.6 68.7 62.6 76.1 6.88 0.332Parietal notch 62.7 61.1 58.1 58.5 65.2 68.3 80.4 3.75 0.710

1 Craniosynostosis group was not included in sagittal wormian bone analysis.2 Fronto-vertico-occipital deformation.3 Parallelo-fronto-occipital deformation.4 Since one cranium (no. 276981) in craniosynostotic group also had lambdoid synostosis, only 6 of 7 craniosynostotic crania were usedto analyze lambdoid wormian bone frequency.* Significant at P 0.05.

TABLE 4. Kruskal-Wallis ANOVA results, comparing collapsed cranial groups with number of wormian bones1

Wormian bonetype

Mean rank values for cranial group ANOVA valuesUndeformed

(n 35)Simple deformation

(n 39)2Complex deformation

(n 45)3Chi-square

statistic P-value

Coronal 55.3 66.3 58.2 2.82 0.245Pterionic 57.3 56.6 65.1 3.87 0.144Sagittal 58.5 63.1 58.5 6.26 0.044*Apical 53.6 62.9 62.5 2.55 0.279Lambdoid 45.5 71.5 61.3 10.67 0.005**Asterionic 57.8 60.8 61.0 0.25 0.883Parieto-mastoid 56.7 61.2 61.5 1.91 0.384Occipito-mastoid 57.7 64.8 57.6 2.06 0.357Squamosal 57.1 60.1 62.1 1.98 0.372Parietal Notch 60.2 58.0 61.6 0.38 0.827

1 Craniosynostosis group was not included in this analysis.2 Simple deformation group includes occipital and lambdoid deformed crania.3 Complex deformation group includes fronto-vertico-occipital, parallelo-fronto-occipital, and annular deformed crania.* Significant at P 0.05.** Significant at P 0.01.



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an increased number of lambdoid wormian bones,as seen in this study. The craniosynostotic grouphad a slightly decreased frequency of coronal

wormian bones. Redirected cranial growth vectorswould not have a positive effect on coronal ossiclefrequency if these anteriorly placed ossicles areunder greater genetic control.

Per the hypothesis of Anton et al. (1992), in-creased compression at sutures could explain whysome deformational groups had lower frequencies ofsome wormian bones. For example, annular and par-allelo-fronto-occipital deformation both place com-pression at the occipito-mastoid sutures, and thesegroups also have fewer occipito-mastoid wormianbones. In contrast, occipital deformation does notdirectly compress the entire lambdoid suture, so itmay produce tension at parts of the lambdoid suture

and thereby produce greater frequencies of lambdoidossicles. Lambdoid deformation compresses thelambdoid suture directly, but since the lamboidgroup was small and necessarily restricted to theSouthwest US, another unknown factor may be re-sponsible for lambdoid ossicle formation in thisgroup.

Degree-of-deformation data (Table 5) show thatthe posteriorly-placed lambdoid, apical, and aste-rionic bones appear in greater frequencies in mod-erate and marked deformed crania. With few ex-ceptions, anteriorly placed ossicles are seen insimilar frequencies among all degree groups. Dueto sample-size limitations, the degree of deforma-

tion within a particular group (e.g., occipital)could not be examined. As a result, type-specificinformation about degree of deformation cannot bedetermined. It would be interesting to know if, forexample, crania with marked occipital deforma-tion exhibited greater frequencies of wormianbones than crania with slight occipital deforma-tion.

The data show that posteriorly placed wormianbones appear in greater numbers in deformed cra-nia. The data cannot answer whether cranial defor-mation affects the initial presence or absence ofthese ossicles. Previous animal studies yielded in-

consistent results. While Pucciarelli (1974) foundthat both anterior deformation and posterior defor-mation resulted in a similar increase of both ante-

rior and posterior sutural bones in 21 rats, 77 otherdeformed rat crania exhibited no sutural bones, sug-gesting that deformation did not affect sutural bonepresence. Burrows et al. (1997) noted in their rabbitstudy that coronal wormian bones appeared afterthe coronal suture was experimentally immobilized,but as they were unable to examine the sutures inutero, it is not clear whether wormian bones werepresent before or after synostotic changes occurred.Ultimately, the question about genetic vs. environ-mental influence on wormian bone formation maybest be answered in the future with fetal animalcrania studies.

This study provided preliminary data and hypoth-

eses to explain wormian bone formation. More re-search is necessary, using larger adult sample sizes,juvenile human crania samples (Dean, 1991), andanimal studies to further test these hypotheses.

ACKNOWLEDGMENTS

Crania were provided by Indiana University(Bloomington, IN), the Thomas Gilcrease Instituteof American History and Art (Tulsa, OK), and theNational Museum of Natural History, Smithso-nian Institution (Washington, DC). I thank theseinstitutions for granting me access to the skeletalcollections and for assisting me whenever possi-ble. I appreciate the helpful comments of the anon-

ymous reviewers of this manuscript. I thank PaulJamison of Indiana University for his assistancewith statistical analysis. Finally, I am indebted toDavid Hunt, Physical Anthropology CollectionsManager at the Smithsonian Institution, for hisguidance and assistance with my research duringmy 7-month stay.

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TABLE 5. Kruskal-Wallis ANOVA results, comparing posterior degree of cultural deformation with number of wormian bones1

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1 All culturally deformed groups were combined into one big group, and then resorted by degree of posterior flattening. Craniosyn-ostosis group was not included in this analysis.* Significant at P 0.05.

154 V.D. OLOUGHLIN


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