2.2 Measurements of skull dimensions
A single observer measured the skull height, length and width (MM) using
X-ray images of the alcohol preserved specimens, as described by Lázaro
et al. (2017). Briefly, skull length was measured from the anterior-most
projection of the first incisive tooth to the occipital condyle (Figure
2a); skull height was measured from the dorsal outline of the braincase
to the orthogonal line defined by the ventral outlines of the pterygoid
process and occipital condyle, passing over a constant proportional
distance on the line defined by the skull length (Figure 2a); skull
width was the greatest lateral diameter of the braincase (Figure 2b).
The technical error of measurement (standard deviation of the repeated
measurements of the same individual as the % of the mean) for the skull
length, height and width was 1.35%, 2.04%, and 1.89%, respectively
(supplemental information in Lázaro et al. 2017). We measured a total of
503 skulls.