Megaloolithid dinosaur eggs: scrambled parataxonomy and nesting strategies

The detailed study of fossil dinosaur eggshells from Upper Cretaceous continental deposits
from the Hateg Basin (Romania), the Arc Basin and Argentina and from the Thanetian of the
Rians Basin (France) was made in order to test the robustness of fossil eggs' parataxonomy
and to reveal novel data on dinosaur palaeobiology. µXRF, XRD and cathodoluminescence
analyses attest a limited diagenesis on these fossils, which allow interpreting observed traits
from a palaeobiological point of view. According to their microstructure, analysed eggs
mainly belong to the titanosaur-related Megaloolithidae oofamily. Measured histological
variables analysed through PCA - clustering unveil a weak megaloolithid parataxonomy
scheme which needs to include whole shell units morphology forming the eggshell in addition
to descriptions. XRD analyses point to an almost pure calcite eggshell composition (LMC)
as well as a preferential orientation of this calcite along the shell unit growth axis, the latter
involving biomechanical properties of the egg. Water vapour conductance (GH2O) estimation
of some fossil eggshells together with the corresponding porosity - modelled mass pairs
suggest that Hat eg and Arc Basins titanosaurs burrowed their nest in humid conditions. The
vegetation-mount hypothesis is rejected whereas a hydrothermal environment is proposed for
the Argentinian sample.