Figure S1. Geometric morphometric analyses of the lateral view of the heads of six Psammophylax species. Warped outline diagrams to the left of the boxplots of the principal component scores for the first three PC axes represent the shape changes at the positive and negative extremes of each axis. Boxplots show the median values (thick central line), upper and lower quartiles (box edges), and the highest and lowest values (error bars), excluding the outliers (circles).

Figure S2. Geometric morphometric analyses of the dorsal view of the heads of six Psammophylax species. Warped outline diagrams to the left of the boxplots of the principal component scores for the first three PC axes represent the shape changes at the positive and negative extremes of each axis. Boxplots show the median values (thick central line), upper and lower quartiles (box edges), and the highest and lowest values (error bars), excluding the outliers (circles).

Table S1. Results of the HSD post‐hoc tests for the principal component analyses (PC) for the dorsal (DC) and lateral (LC) view of the heads. The difference values (diff.) and the p‐values (P‐value) are shown. Significance (P = 0.05) is indicated with bold italic font.