The titanosaurs egg clusters found in the Narmada valley outcrops in central India. Credit: G. V. R. Prasad

Geologists from University of Delhi have found an unusually large number of nesting sites1 and 256 fossil eggs and their fragments in the lower Narmada valley, on outcrops spanning 2.5 km2 across five villages in Madhya Pradesh, central India.

The eggs, estimated to be 66 million years old, were laid by titanosaurs, the largest dinosaurs to have roamed the planet. The plant-eating giants laid their eggs in shallow pits and buried them in nests along the shores of waterbodies in marshes.

Reproductive behaviour like birds and turtles

The team found the dinosaur nests during their field trips between 2017 and 2020. They identified almost intact circular or fragmented egg outlines, hatched and unhatched eggs, eggshell fragments, bottom surfaces of eggs, hatching windows, pathological eggs (eggs with two shells) and compressed eggs.

There were more hatched eggs than unhatched ones, which were possibly buried too deep for the embryos often to survive.

The researchers said that the short distance between nests, and different egg species indicated that titanosaurs nested in colonies. The titanosaurs also laid pathological eggs, often attributed to physiological or environmental stress. These findings suggest that the dinosaurs had a reproductive physiology and nesting pattern similar to that of modern birds.

“This nesting pattern possibly protected the hatchlings from predators,” said Harsha Dhiman, a geologist and the study’s lead author at University of Delhi.

The nesting sites didn’t yield any fossil bones of embryo, juvenile, or parent dinosaurs, probably because the dinosaurs did not live where they laid their eggs, Dhiman said.

The tightly packed nests also indicate that the adult titanosaurs left the nests soon after laying the eggs, leaving the hatchlings to crawl out and fend for themselves. “This suggests that parental care did not exist among titanosaurs as the parents’ large size increased the chances of crushing the eggs,” Dhiman said.

“It is highly unusual to find such an astonishing number of dinosaur nests in a relatively small area,” said Darla Zelenitsky, a palaeontologist at University of Calgary in Canada, who was not involved in the study. “The nesting sites are important as they can help us understand if dinosaurs nested in rookeries or colonies like many birds and if they cared for their young.”

“The size difference between the dinosaurs and the hatchlings would be somewhat akin to an adult pigeon caring for hatchlings the size of an ant,” she pointed out.

Since the nests were unguarded, eggs and young were vulnerable to predators. The dinosaurs overcame this by laying more eggs for a potentially higher return of hatchlings. The lack of parental care is very similar to that among turtles, the researchers say.

The staggering number of nests similar to those found in Argentina, Spain and China, indicate that titanosaurs may have nested together, said Dhananjay Mohabey, a geologist formerly at the Geological Survey of India.

Further isotope-based research on the eggshells could provide information on the environmental temperature, variable thermoregulation and body temperature of this extinct group of reptiles, he said.

But the researchers have other theories about why titanosaurs would lay so many eggs. “We think the Indian dinosaurs were already undergoing some decline in their diversity by the end of the Cretaceous period and they were possibly trying to increase their chances of survival by laying these many eggs,” said geologist, and lead researcher, Guntupalli V. R. Prasad, of Delhi University.

Researchers contend that Indian dinosaurs died before the Cretaceous-Tertiary boundary around 66 million years ago. “Large numbers of hatcheries representing the increased population size of various species of Indian dinosaurs could be a prelude to their extinction strongly linked to Deccan volcanism that erupted between 67 and 62 million years ago,” Mohabey noted.