Data from: Comparative crystallography suggests maniraptoran theropod affinities for latest Cretaceous European ‘geckoid’ eggshell

Thin fossil eggshells from Upper Cretaceous deposits of Europe,
characterized by nodular ornamentation similar to modern gekkotan
eggshells, have mostly been interpreted as gekkotan (=‘geckoid’) in
origin. However, in some cases, like the oogenus Pseudogeckoolithus, their
theropod affinity was also suggested. The true affinity of these fossil
‘geckoid’ eggshells remained controversial due to the absence of
analytical methods effective in identifying genuine gecko eggshells in the
fossil record. In this study, we apply electron backscatter diffraction
(EBSD) analysis to latest Cretaceous European 'geckoid'
(including Pseudogeckoolithus) eggshells, in comparison with modern
gekkotan and theropod (avian) eggshells. Our results show that
Pseudogeckoolithus has a definite theropod eggshell-like crystallographic
configuration, in clear contrast to that seen in modern geckos.
Furthermore, the crystallography of the nodular ornamentation in
Pseudogeckoolithus is comparable to that seen in megapode eggshells, but
different from that of gecko eggshells, despite superficial morphological
similarity. The remarkable morphological similarities between
Pseudogeckoolithus and modern gecko eggshells are thus convergent, and the
‘gekkotan affinity’ hypothesis can be dismissed for Pseudogeckoolithus.
This study provides a template for differentiating true gekkotan from
dinosaurian eggshells in the fossil record. The potential functional
significance of eggshell ornamentation, lost in most modern birds,
requires further study, and experimental zoological approach may shed
light on this issue. Finally, our results caution about the dangers of
using potentially homoplastic eggshell characters in eggshell
parataxonomy.