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.