The similarity of preferred orientation development in eggshell calcite of the dinosaurs and birds

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By using X-ray diffractometry, the development of preferred orientation of the calcite was determined for the eggshells of species of Upper Cre­taceous dinosaurs from North America, the Mediterranean, Mongolia and China. In all except one specimen, which was shown to be recrys­tallized, a texture develops throughout shell deposition such that the (001) plane becomes increasingly more aligned parallel to the shell sur­face. The rate of texture development changes at clearly defined points, in contrast to that in the shells of the extant reptiles. During the initial stage of shell deposition, texture development is unhindered and deter­mined only by the column radius. The pattern of preferred orientation development is thus identical to that previously established for the thick ratite shells. It is proposed that such a configuration of texture dev­elopment in the dinosaurs can arise only through hindrance during deposition by the sheet-like organic component of the shell, as has been shown to occur in the avian eggshell. The organic component, which functions as a reinforcing fibrous network that ties the shell columns together, must originally have been laid down in the dinosaur eggshells in a manner similar to that in the birds, suggesting a similarity in the physiology of eggshell deposition.