Eggs belong to 6 species, suggesting a higher diversity of these extinct giants in India
Fossilised eggs provide clues on reproductive biology, nesting behaviour and parental care. Image: iStock._ A group of Indian researchers found rare cases of fossilised dinosaur eggs — an egg within an egg — among 256 newly discovered eggs from the Narmada Valley. The discovery suggests that Titanosaurs — one of the largest dinosaurs to have roamed the Earth — displayed a notable reproductive trait unique to modern-day birds. The findings of the study are published in the journal PLoS One January 18, 2023.
“The unique feature of egg within the egg has not been reported from any other dinosaur or even in other reptiles,” Harsha Dhiman from the University of Delhi and the lead author of the study told Down To Earth.
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The egg has two yolks; this feature can be seen in birds, suggesting they share similar reproductive traits, the expert explained.
The team discovered 92 nesting sites containing 265 fossilised eggs — measuring 15-17 centimetres in diameter — during field investigations in the Dhar district of Madhya Pradesh between 2017 and 2020.
This region falls between the easternmost Lameta exposures at Jabalpur in the upper Narmada Valley (central India) and Balasinor in the west in the lower Narmada Valley (western central India), according to the document.
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Credit: Dhiman et al., 2023, PLOS ONE, CC-BY 4.0
Lameta exposure is a sedimentary rock formation known for its dinosaur fossils. “These sedimentary rocks are mostly exposed along the Narmada Valley,” Dhiman explained. The fossil records here are largely concealed by Deccan volcanic flows, which prevents their removal by erosion.
The eggs belonged to six species, suggesting a higher diversity of these extinct giants in India. Further, Titanosaurs buried their eggs in shallow pits, a behaviour seen in modern-day crocodiles.
They nested in colonies, a feature found in about 13 per cent of modern-day birds. They also laid eggs in sequential order like avian species.
Parental care was likely absent as the eggs were laid too close to each other. The spacing did not provide room for adults, suggesting that hatchings were forced to fend for themselves, the study added.
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Dhiman speculates that the “egg-in-egg feature” did not benefit the dinosaurs. The pore canals get blocked due to the presence of two eggshell layers, one above the other. This could asphyxiate the embryo, she added.
Among the fossils, the team also found unhatched eggs. Infertility, embryo death before hatching and deep burial could have contributed to their death. Environmental factors such as floods could also be involved, the researchers noted.
Fossilised eggs provide clues on reproductive biology, nesting behaviour and parental care, according to Dhiman.
“Moreover, stable isotope studies of eggshells can help us understand the diet and the type of water consumed and the environment in which the eggs were deposited,” the expert explained.
The team hopes to study fossil bone and teeth specimens from the Lameta Formation of Narmada Valley. They also plan to scan the eggs to search for embryo or juvenile fossil specimens.
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