Intertrait Correlations by Trait Type and Trait Region Both trait type and trait region were analyzed for intertrait correlation in order to

to levels of correlation. Trait type analyses will be discussed first, followed by the discussion of the regional analysis.

For hypostotic traits and traits relating to foramina or canals in both the male and female populations, intertrait correlation occurred at a level either equal to or below that expected by chance. This low level of intertrait correlation implies that the hypostotic traits and the foraminal traits in this study are independent of one another, and can be used in genetic distance analysis without problem.

Intertrait correlation in the hyperostotic class of traits occurred at approximately four times the level expected by chance at the 0.01 significance level. This high level of intertrait correlation suggests that not all of the hyperostotic traits are independent of one another. In the male population, the four significant

correlations at the 0.01 significance level are Ps/Mh, Cl/Ca, Ca/Dj, and Ca/Mh. In the female population, the four significant correlations at the 0.01 level are

Ps/Mh, Cl/Ca, Ts/Mh, and Pt/Oa.

Because the mylohyoid groove (Mh) is located on the mandible, correlations with that trait do not have a regional explanation, and are more likely to be explained, as in this case, by trait type. The pterygospinous spur (Ps), clino-clinoid bridge (Cl), and carotico-clinoid bridge (Ca) are all located on the sphenoid bone, meaning that in addition to being hyperostotic traits, there may be a regional explanation for the correlation between the three traits. The precondylar tubercle (Pt) and ossified apical ligament (Oa) are both located at the anterior aspect of the foramen magnum, indicating a possible regional explanation for this

correlation as well. In this case, it is important to eliminate the most highly correlated traits for genetic distance analysis in order to avoid overstatement of the significance of the mean measure of divergence calculation. In this particular case, it is suggested that the carotico-clinoid bridge (Ca), and mylohyoid groove (Mh) be eliminated from any distance analyses conducted on the Dakhleh population.

For the ossicles, intertrait correlation occurred at a much higher level than would be expected by chance – greater than six times what would be expected by chance for the male population at the 0.01 significance level and greater than seven times what would be expected by chance for the female population at the 0.01 significance level. In the male population, the significant correlations at the 0.01 level are So/Po, Lo/Pn, Lo/Sq, As/Pn, Om/Pn, and Pn/Sq. In the female population, the correlations significant at the 0.01 level are Co/As, So/Lb, So/As, Lo/Pn, As/Om, Pn/Sq, and Sq/Po. Overall, there is a very high level of correlation between the ossicles.

In some cases, it has been suggested that ossicles should be grouped together as one nonmetric trait for the purposes of genetic distance analyses because of their high degree of correlation (Ossenberg 1976). In other cases, the ossicles correlated the least with other ossicles have been kept in the analysis. For example, Molto (1983) retained the pterionic ossicle in his study of Ontario Iroquoian crania because he found it to be virtually independent of all other accessory sutural ossicles. The lambdic bone was also included in the study because it was found to be associated with all of the other ossicles, and it is the least ambiguous ossicle to score, thus reducing observer error (Molto 1983). In this case, however, the lambdic ossicle (Lb) was not highly correlated with all other ossicles – in the males it was uncorrelated with any other ossicle at the 0.01 level, and in females only one significant correlation was present, that with the sagittal ossicle (So).

The different methods used for the handling of ossicles in nonmetric trait analysis owes to the large amount of between-population variability. It is therefore

important to test for intertrait correlation in any population being studied in order to appropriately eliminate the most highly correlated traits from further analysis. In this case, the most highly correlated ossicles that would be removed if the mean measure of divergence were to be calculated are the parietal notch ossicle (Pn),

squamosal ossicle (Sq), asterionic ossicle (As), sagittal ossicle (So), and lambdoidal ossicle (Lo). The accessory ossicles in the analysis that have no significant correlations amongst one another are: the coronal ossicle (Co), bregmatic ossicle (Bo), lambdic ossicle (Lb), occipito-mastoid ossicle (Om), and the pterionic ossicle (Po).

Regional correlations in the basiocciput region of the skull were analyzed in order to investigate Barnes’ (1994) hypothesis of cranial shifting as a developmental field defect. Barnes states that there is a strong tendency for shifts to occur at the craniovertebral border, and that these shifts are genetically linked. If this cranial shift has an influence on the presence of nonmetric traits, it would be expected that the nonmetric traits of the basiocciput region (a number of which have been posited by Barnes to be expressions of a cranial shift) should occur together and at significant levels of correlation. Regional analysis was conducted for the traits of the basiocciput – the divided hypoglossal canal (Dh), precondylar tubercle (Pt), ossified apical ligament (Oa), intermediate condylar canal (Ic), pharyngeal fossa (Ph), and notochord remnant (Nr). In the male population subset, there were no significant correlations between these six traits at the 0.01 significance level, which is what would be expected by chance. In the female population subset, there was one significant correlation at the 0.01 significance level (Pt/Oa), which is slightly higher than what would be expected by chance. Additionally, a previous study found complete independence of the six nonmetric traits located on the atlas bone (which would also be affected by a shift at the craniovertebral border) (Edwards 2005). The lack of correlation between the traits of the basiocciput and also between the traits on the atlas suggests that cranial shifting is not a factor contributing to the expression of nonmetric traits at the craniovertebral border. Thus, the Barnes hypothesis is rejected for this population.