Figure 4

An example of intra-species (A, B) and inter-species (C, D) quantitative morphological comparison using CT scans of seven anthropoid and seven strepsirrhine skulls. Intra-species comparison. (A) Red circle encloses average anthropoid skull computed from the surrounding 7 individual skulls using SYMREG. Similarity values for individual skulls compared with the template is show as the red dot on the plot with scores on the vertical axis. (B) Blue circle encloses average strepsirrhine skull computed from the surrounding 7 individual skulls using SYMREG. Similarity values for individual skulls compared with the template is show as the blue dot on the plot with scores on the horizontal axis. Scores are high in all cases, as would be expected, and suggest each skull is from the same species. Variations provided by variations from the mean form a basis for quantitative comparision. Inter-species comparison. In (C) the average strepsirrhine from (B) is used for the comparison template for the seven anthropoid skulls in (A). The similarity values (pointed to by red dotted line) are all low, suggesting each is a poor match in species. In (D) the average anthropoid from (A) is used for the comparison template for the seven strepsirrhine skulls in (B). Again, the poor similarity scores (pointed to be blue dotted line) suggest that the species are different. Note that while the similarity measure here (mean squared difference) is a simple scalar values, it is derived from the volumetric differences between individual skulls and templates which can be used to identify specific locations of geometric variations.