Effects of different kinds of cranial deformation on the incidence of wormian bones.

Researchers have debated whether the presence and frequency of wormian bones (sutural bones, supernumerary bones, and ossicles) are attributable to genetic factors, environmental factors, or both. This research examines the effects of many different kinds of cranial deformation on the incidence of wormian bones. A sample of 127 deformed and undeformed crania from New World archaeological sites was examined. An undeformed cranial sample (n=35) was compared to the following cranially deformed groups: 1) occipital, 2) lambdoid, 3) annular, 4) fronto-vertico-occipital, 5) parallelo-fronto-occipital, and 6) sagittal synostosis. Three levels of degree of cultural cranial deformation were qualitatively determined. Type and number of wormian bones along each major suture were recorded for each cranium. Group means were analyzed using Kruskal-Wallis one-way ANOVA statistical tests to test the null hypothesis that cranial deformation does not have an effect on wormian bone incidence. Results indicate that all forms of cranial deformation affect the frequency of some types of wormian bones. In particular, all cranially deformed groups exhibited significantly greater frequencies of lambdoid ossicles. Apical, parieto-mastoid, and occipito-mastoid wormian bones also appeared with greater frequency in some groups of culturally deformed crania. Further, varying degrees of cultural deformation all had more lambdoid wormian bones than the undeformed group. These results suggest that wormian bone development in posteriorly placed sutures may be affected more by environmental forces than are their anteriorly placed counterparts.