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Shawkey, M. D. & D’Alba, L. Egg pigmentation probably has an Archosaur origin. Nature https://doi.org/10.1038/s41586-019-1282-4 (2019).
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We thank D. E. G. Briggs for assistance with the manuscript, and M. Fabbri and J. Gauthier for suggestions.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
a, The outer eggshell surface (n = 1), which contains the highest pigment concentrations in eumaniraptorans is uncoloured/white. b, c, The inner eggshell surface (n = 2) shows a reddish tint (b), which reflects chorioallantoic tissues and vascularity (c) protruding into the innermost layers of the eggshell. The inner eggshell surface in b is manually cleaned of adjacent chorioallantoic tissue, whereas the inner eggshell surface in c is left untreated. Chorioallantoic tissues (c) are commonly vascularized, and therefore saturated in blood-derived haem, which represents, when dechelated, protoporphyrin. In this case, traces of protoporphyrin recovered from Crocodylus siamensis eggshell would not be homologous with eumaniraptoran eggshell protoporphyrin.