Wormian bones in Finnish samples : morphology, morphogenesis, and the influence of cranial shape, sex, and regional variations

Abstract

This master’s thesis examines the occurrence of wormian bones in Finnish samples, focusing on their morphology, morphogenesis and the potential influences of cranial shape, sex, and regional variations. Wormian bones are small accessory bones that occasionally form in the sutures of the cranium. Although they are a common occurrence with no direct pathological implications according to contemporary knowledge, their occurrence varies largely between populations. The mechanisms behind their formation also remain unclear.

Data was collected from 104 crania from three regions of Finland: Northern Ostrobothnia, Ostrobothnia, and Uusimaa. The samples belong to the archeological collections of the University of Oulu and the osteological collections of the Finnish Museum of Natural History (Luomus). Methods included osteometric and morphological assessments and later statistical analyses on the data. Assessments included cranial measurements, sex estimation, and the measuring and classification of wormian bones.

Wormian bones were present in 80% of the individuals, which can be considered a remarkably high frequency. Predominant locations were the lambdoidal suture as well as other posterior parts of the crania, with no statistical differences found between sexes or regional groups. Cranial shape was however found to potentially influence the presence of wormian bones, with longer crania having a slightly higher frequency of wormian bones occurrence. Additionally, it was discovered that crania with abnormally high counts of wormian bones tended to be relatively broad in shape.

A high level of consistency in the occurrence of wormian bones was discovered both between sexes and regions, suggesting environmental or biomechanical factors over solely genetic or biological predisposition. This idea was also supported by the inclusion of a Finland-Swedish sample, which showed consistent results with the general Finnish population, while potentially being more genetically distant from them. A potential connection to vitamin D deficiency was proposed, given its known effects if softening the bones which could in turn cause wormian bones to form in the cranium due to the added pressure to the sutures. While genetic influence cannot be ruled out, it is more likely other factors influenced the high occurrence of wormian bones in the Finnish samples. Further research on the topic would be vital in discovering the true causes for the formation of these ossicles.