The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Modularity and integration in the human cranial vault


Applied Forensic Sciences, Mercyhurst University

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Previous research on morphological integration and modularity of the cranium has focused on larger functional units of the vault, base, and face. However, comparatively few studies have explored patterns of modularity and integration within these divisions, in particular the vault. The present study analyzes variation along the midsagittal outline of the human cranial vault for interactions among the frontal, parietal, and occipital bones. Arc lengths and measurements including chords, subtenses, and fractions in the midsagittal plane were collected from 130 crania of known sex and ancestry from the Hamann-Todd Collection at the Cleveland Museum of Natural History, and were compared using correlation matrices and principal components analysis (PCA).

In contrast to most PCA results using craniometric data, our results show a much lower proportion of total variation in PC1 (38%), indicating that integration is relatively lower in the vault module in terms of allometric size. PC2 and PC3 represent a combined 41% of the total variation and display modularity of bones through high magnitude loadings with distinct variation vectors corresponding to each bone’s measurements, specifically in the parietal (PC2) and the frontal (PC3) bones. The PCA results indicate that the three bones vary largely independently from each other in terms of shape. Therefore, modularity appears to influence patterns of phenotypic variation within the vault at least as much as integration.

This study suggests that bones in the midsagittal plane behave as modular units, and that studying the cranial vault as a single module masks important variation patterns within each subunit.

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