Data from: Biogenic origin of secondary eggshell units in dinosaur eggshells elucidates lost biomineralization process in maniraptoran dinosaurs

Although rarely seen in modern avian eggshells, secondary eggshell units
are remarkable structures in non-avian dinosaur eggshells and provide
paleobiological information. However, the origin of secondary eggshell
units has rarely been studied, which has resulted in controversies in
paleontology because abiogenic origin has also been suggested for the
formation of secondary eggshell units. Here, we show that secondary
eggshell units of non-avian dinosaur eggshells are biogenic structures
using a combination of microscopic techniques, mainly electron backscatter
diffraction (EBSD) and scanning electron microscope (SEM). The features of
secondary eggshell units suggest that the formation mechanism of
non-maniraptoran dinosaur eggshells is comparable to that of turtle and
crocodile eggshells. Matrix fibers appear to be the initiators of
secondary eggshell units. A weakening trend of secondary eggshell units
toward non-avian maniraptoran dinosaurs supports that maniraptoran
dinosaurs evolved a more organized physiological mechanism of eggshell
formation.