The position of Natrix tessellata specimens from the ‘Europe’ and ‘Greece’ clades within the morphospace from the dorsal (A) and ventral (C) parts of the cranium with the three-dimensional models and dissected braincases correlated with the PC1 and PC2 axes, along with the coloured deformation grids (B, D). Cooler colours indicate a higher amount of stretching, hotter colours indicate a higher amount of compression. Borderline specimens are in bold and the numbers assigned to the specimens correspond to those listed in Table S5. The scale bar indicates 1 mm.