Fig. 4.

Ratite egg phylogeny and eggshell strength. (A) Phylogeny of ratites based on extensive mitochondrial DNA sequencing (1, 2, 6, 32). The light grey line indicates the uncertain position of Mullerornis within the tree (32). Relative egg sizes are shown based on volumes calculated from shape dimensions or shell thickness (4, 22, 23). A dark grey chicken egg is shown in the light grey box (Bottom Left) for size comparison. (B) Egg breakability factors (S) calculated using mass of the incubating bird and egg thickness (Table S3). Blue indicates males, red indicates females, grey indicates no (or unknown) sexual dimorphism.