Fig. 4

Bivariate morphospaces depicting the convergent evolution of skull roof traits. Converging morphospace ellipsoids are defined by the phenotype of the fully fossorial clades (coloured tips). The convergence index C5 [45] corresponds to the number of lineages entering this space. As indicated by univariate C1 (see top left legend box diagram), compactness and diameter (a, b) are strongly converging—with (b) showing an enlarged excerpt of (a) in accordance with the dashed line. The ratio of frontal and parietal rfp and elongation (c) are weakly converging, while overlap and thickness (d) are not converging. For key to tip abbreviations, see Additional file 1: Table S6