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. 2023 Jan 31;12:e81092. doi: 10.7554/eLife.81092

Figure 3. Emu eggshell.

Note that deposition of granular layer (GL) begins in the EZ. Scale bars equal 500 µm.

Figure 3.

Figure 3—figure supplement 1. Previous and current interpretations on the microstructure of casuariid eggshells.

Figure 3—figure supplement 1.

(A,C) Mikhailov, 1997a and Grellet-Tinner, 2006 suggested four layers. (B) Zelenitsky and Modesto, 2003 suggested that compact calcified part of the eggshell is composed of SqZ and Resistant Zone is an extension of SqZ. In their view, ornamentation is a homologous structure to EZ that is usually present in all avian eggshell (except for passerine; Mikhailov, 1997a). (D) Lawver and Boyd, 2018 pointed out that ornamentation has its ‘root’ inside compact calcified eggshell. It was confirmed in Choi et al., 2020 and this study. In addition, based on the GB condition of EZ, which is characterized by linear line, Choi et al., 2020 further suggested that outer compact calcified part of the eggshell is EZ, not SqZ as suggested by Zelenitsky and Modesto, 2003. In our view, therefore, ornamentation is not homologous to EZ of most avian eggshells, but is an autapomorphic character of MRCA of emu and cassowary.