Phylogenetic positions and biomineralization of eggshell proteins of turtles

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We performed immunological assays on the extracts from eggshells of reptiles and birds. The results support that the archosaurian affinity of turtles. Raman measurements showed that eggshells of turtles are aragonite, whereas those of snakes, lizards, crocodiles and birds are calcite. We examined the ion composition in the secretions of the oviducts of soft-shelled turtles and hens. Under both the conditions, not aragonite but calcite is expected to be formed, suggesting that the switch between the polymorphs may be controlled by proteins.