In December 2021, scientists found a 66-million-year-old dinosaur embryo inside a fossilized egg in China. The specimen is one of the most complete dinosaur embryos known, and in particular is closer in posture to those seen in bird embryos than those generally found in dinosaurs.
Now, a new finding that disturbs what we knew until now about dinosaurs. A team of paleontologists has discovered the first dinosaur “egg within an egg” in India. This egg was found in a titanosaurid dinosaur nest dating back to the Lameta Formation of the Late Cretaceous, from about 66 million years ago to 100 million years ago. It is a truly exceptional find.
This type of egg has only been observed in birds (such as chickens, for example) and arises when an egg is pushed into the mother’s reproductive system and embeds with another newly formed egg. And it is that birds have a specialized uterus that lays one egg before going to work on the next, which is believed to be related to the formation of these misshapen double eggs. This new finding indicates that in ovo ovum pathology is not unique to birds and that dinosaurs could have a similar reproductive role.
An egg inside an egg
The egg-within-an-egg came from a titanosaurid dinosaur, revealing clues about its oviduct morphology, which was likely more similar to that of birds that are well-adapted for sequential egg-laying. The microstructure of the pathological egg and that of an adjacent egg in the same nest was associated with that of titanosaurid sauropod dinosaurs, according to a university statement. What would it indicate? That this group of sauropod dinosaurs were also capable of hatching egg after egg, like their current relatives.
The egg was found in a place called Nest p7 at the dig site where other dinosaur fossils have been found, including eggs, but all of them from titanosaurs. Fossils of this type of sauropod dinosaur are widespread and are found on every modern continent on the planet.
Specifically, the eggs were found in the sandy limestone/calcareous sandstone of the lower Narmada Valley. During multiple fieldwork conducted by the authors in the Bagh-Kukshi areas of Dhar district, 108 titanosaur nests were identified, including intact clutches, isolated eggs, and various eggshell fragments.
Titanosaurs were the last surviving group of long-necked sauropods, and the taxa were still thriving at the time of extinction at the end of the Cretaceous . The team found a total of 52 nests in the area near the village of Padlya, near the city of Bagh. The fossilized egg under study was found in a nest with a total of 11 dinosaur eggs.
What it’s like?
The extraordinary egg has two continuous, circular shell layers separated by a wide gap, and its fossilized remains make it clear that it is an egg within an egg. “The cross-sectional outline of the pathological egg shows a physical organization of the two layers of the shell similar to that of ovules in eggs previously reported in birds. This opens the possibility that titanosaurids may have adapted for sequential laying .” of eggs,” the authors explain.
Although the authors insist that more research is needed to draw firm conclusions, the discovery of this unusual egg demonstrates that this oological peculiarity is not exclusive to birds. And it also suggests that sauropods had more in common with birds and crocodilians than with non-archosaur reptiles. A find of global proportions.
Referencia: Harsha Dhiman et al, First ovum-in-ovo pathological titanosaurid egg throws light on the reproductive biology of sauropod dinosaurs, Scientific Reports (2022). DOI: 10.1038/s41598-022-13257-3
