‘Abnormal’ dinosaur egg in India digs up new questions for evolution

‘Abnormal’ dinosaur egg in India digs up new questions for evolution

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A team of researchers from the University of Delhi has discovered a unique set of fossilised dinosaur eggs, with one egg nesting within the other at the Dinosaur Fossil National Park, in Dhar District of Madhya Pradesh. While eggs-within-eggs are rare phenomena, they are so far known to occur only in birds and have never known in reptiles. This discovery brings out newer connections between reptilian and avian evolution.

The findings, published in the journal Scientific Reports, talk about the ‘egg-in-egg’ phenomenon in a titanosaurid dinosaur egg found from the Bagh area of Dhar District in Madhya Pradesh

Dinosaurs of the Sauropod family were among the largest land animals that have ever lived and were widespread millions of years ago in the territory that is now India. Fossils of these animals have been found in Gujarat, Madhya Pradesh as well as Meghalaya.

The Upper Cretaceous Lameta Formation of Central India is long known for its dinosaur fossils (both skeletal and egg remains), and scientists, some of whom were involved in the team reporting the latest findings, documented 52 titanosaurid sauropod nests near Padlya village close to Bagh town in Madhya Pradesh. One of these nests consisted of 10 eggs, one of which was the “abnormal” egg.

Big find: The site from where the eggs were dug up at Bagh in Dhar district of Madhya Pradesh. 
| Photo Credit: Special Arrangement

The egg has two continuous and circular eggshell layers separated by a wide gap like that observed in birds. Until this discovery, no egg-in-egg fossil egg was found in dinosaurs and other reptiles such as turtles, lizards, and crocodiles.

It was believed that dinosaurs had a reproductive function similar to that of turtles and other reptiles (unsegmented oviduct) in contrast to segmented reproductive tract of crocodiles and birds with separate regions of membrane and shell deposition.

Although crocodiles have separate regions of shell membrane and mineralised shell deposition, they ovulate and release all the eggs simultaneously like turtles and other reptiles. In birds, ovulation is sequenced and eggs are laid one at a time. “The new discovery of an ovum-in-ovum egg, characteristic of birds in titanosaurids are for a segmented oviduct as in crocodiles and birds and possible sequential laying of eggs as in birds,” the authors aver.

“The finding of ovum-in-ovo egg from a titanosaurid nest opens up the possibility that sauropod dinosaurs had an oviduct morphology similar to those of crocodiles or birds and they may have adapted to a mode of an egg-laying characteristic of birds,” said Harsha Dhiman, Department of Geology, University of Delhi, and lead author of the study.

“The new pathological egg is a rare and important find as no ovum-in-ovo egg was found in reptiles until now and as it brings out significant information on whether dinosaurs had a reproductive biology similar to that of turtles and lizards or their immediate cousins crocodiles and birds,” said Prof. Guntupalli V.R. Prasad from the University of Delhi who is the corresponding author of the published article.

Another co-author of the paper, Vishal Verma, from Bakaner Higher Secondary School and who works in the conservation of fossil sites and was instrumental in establishing four local museums said that the “Bagh-Kukshi area holds key to many such wonderful fossil finds provided systematic scientific exploration is carried out as in the present case”.

The new find highlights the fact that Central and Western India hold great potential for dinosaur fossils which may offer important information on dinosaur diversity, nesting behaviour and reproductive biology, the authors note.

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