Representative images are shown. (
a, b) Light and polarized light images of a thin section of an apparently well-preserved Oviraptorid eggshell from Ukhaa Tolgod, Mongolia. ( c) scanning electron microscopy (SEM) image of a cross-section of the eggshell. Pores such as the one indicated are small and rare compared with Titanosaurid eggshells. As pores are often foci for dissolution and secondary mineral formation, this may be a reason for the relatively good preservation of the Oviraptorid eggshells. ( d, e) Light and cathodoluminescence images of an Auca Mahuevo titanosaur layer-2 eggshell showing localized areas of secondary carbonate on the upper and lower surface.( f) SEM image of an Auca Mahuevo layer-4 eggshell. Importantly, energy-dispersive X-ray analysis (EDS) of material infilling Auca Mahuevo eggshell pores found that it was silica-rich clay rather than secondary calcite ( Supplementary Note 3). ( g– i) Light, polarized light and cathodoluminescence images of typical eggshells from the Rousset site in the Provence Basin. Secondary carbonate is often found on the exterior surfaces and infilling the pores of eggshells from this site, as shown in the cathodoluminescence image. In some cases, Rousset eggshells were found to have a strong cathodoluminescence signal from within the main eggshell structure, a clear indication of alteration ( Supplementary Fig. 3). Scale bar ( c) 100 mm); ( ∼ f, i) 200 mm. More examples of this type of analysis and more in-depth interpretations can be found in the Supplementary Note 3 and Supplementary Figs 1–7.