Figure 14. GB mappings, eggshell thickness, and egg size of Palaeognathae.

The green, blue, and purple lines in GB mapping denote the angle range between the calcite grains. All eggshell maps (including IPF mapping of chicken eggshell for comparison) are drawn to scale; note a scale bar at the upper left corner. The silhouettes of palaeognath are drawn to scale (note a human next to elephant bird and a chicken at the lower right corner). Egg shape and size are drawn to scale (Hauber et al., 2014; Stoddard et al., 2017). Two recently extinct lineages are marked by daggers and the extinct Lithorinithidae by a dashed branch. Landing symbols denote potential independent losses of flight (Mitchell et al., 2014; see also Sackton et al., 2019) and flying bird silhouettes denote volant taxa. Sky blue lines show microstructural and crystallographic similarities among tinamou-style eggshells that is attributable to homoplasy. Red lines mean the homoplastic similarities between ostrich-style eggshells. Purple lines represent potential homologies of rhea-style eggshells.

Figure 14—figure supplement 1. Ellipticity and asymmetry of palaeognath eggs.

Note that ellipticity of palaeognath eggs are not confined to certain range. Kiwi egg has maximum ellipticity and ostrich egg has minimum ellipticity. However, in case of asymmetry, palaeognath eggs have low asymmetry compared to neognath eggs. Coloured ranges mark interquartile ranges of both indices. Modified from Stoddard et al., 2017.

Figure 14—figure supplement 2. An alternative interpretation of evolution of palaeognath eggshells assuming that all tinamou-style eggshells are homologous to one another.

In this case, rhea-style eggshells might have been independently evolved at least four times.