Data from: A gravid fossil turtle from the Early Cretaceous reveals a different egg development strategy to that of extant marine turtles

Extant sea turtles develop and lay pliable (flexible) eggs, however, it is
unknown if they inherited this reproductive strategy from their closer
fossil relatives or corresponds to an evolutionary novelty. Here we
describe the first undisputable gravid marine fossil turtle ever found,
from the early Cretaceous of Colombia, belonging to Desmatochelys padillai
Cadena and Parham, which constitutes a representative of Protostegidae.
Using thin sectioning of one the eggs, as well as scanning electron
microscopy coupled with elemental characterization, cathodoluminescence,
and computer tomography we established that Desmatochelys padillai
produced rigid eggs similar to the ones found in some extant and fossil
freshwater and terrestrial turtles, and that at least 48 spherical eggs
are preserved inside this gravid turtle. We performed also a phylogenetic
analysis of several turtle taxa, including some of the extant marine
species, plus the information from the gravid specimen of Desmatochelys
padillai, and we found more support to previous ideas that egg and
eggshell characters lack of strong phylogenetic signal amongst turtle
taxa. We suggest that the development of rigid eggs in the marine extinct
turtle Desmatochelys padillai resulted as an adaptation for eggs-embryos
requirements dictated by the physical attributes of the nesting site