Paleontologists in central India have uncovered 92 preserved dinosaur nests and 256 eggs in an extensive fossilized hatchery. During the Late Cretaceous period, this breeding ground belonged to long-tailed, long-necked titanosaurs.
Combined with other sites previously found nearby, this trove of fossilized nests makes up one of the world’s largest known dinosaur hatcheries.
“Such nesting colonies would have been a sight to see back in the Cretaceous,” Darla Zelenitsky, a dinosaur paleobiologist at the University of Calgary in Canada who was not involved in the study, tells CNN’s Katie Hunt. “The landscape would have been dotted by a huge number of large dinosaur nests.”
Researchers studied these nests from 2017 to 2020 and published their findings Wednesday in the journal PLOS ONE, revealing insights into the dinosaurs’ reproductive habits.
Some 40 species of titanosaurs, a kind of herbivorous sauropod, are known to have lived, and several of them likely used this hatchery. The researchers found evidence of six species—or kinds of dinosaur eggs—at the site.
With so many nests in close proximity, it would have been hard for the massive reptiles to access the site to incubate eggs or feed hatchlings. Likely incapable of stepping delicately through the hatchery without crushing eggs underfoot, titanosaurs presumably were hands-off parents.
Instead, they might have incubated eggs by covering them, likely with sand, the researchers suggest. Laid and buried in shallow pits, titanosaur eggs may have been warmed by sunlight and the heat of the earth. After hatching, the young dinosaurs would have left the clutch quickly.
“It looks like sauropods laid their eggs and then left their offspring to fend for themselves,” Susannah Maidment, curator of dinosaurs at London’s Natural History Museum who was not involved in the study, tells the museum’s James Ashworth.
To that end, the paleontologists did not find any preserved dinosaur remains with the eggs and nests. No evidence of adults—or even hatchlings—was found in the area.
“It could be possible that this area was only for nesting and not for habitation purposes,” Guntupalli Prasad, a study co-author and paleontologist at the University of Delhi in India, tells Gizmodo’s Isaac Schultz in an email. Alternatively, it’s possible “the bones could not get preserved, or are deeply buried or still unexposed and yet to be discovered.”
One find in particular stood out to the researchers: a rare egg-within-an-egg. This phenomenon, called “ovum-in-ovo,” is a known occurrence in birds. It happens when an egg that’s going to be laid gets pushed back into the body and becomes embedded within another egg, usually under stressful conditions like disease, a shortage of food or extreme temperatures. However, this kind of egg has never been identified in a dinosaur—or in any reptile.
This first-of-its-kind find, if confirmed, suggests that titanosaurs had a similar reproductive system to modern birds. They may have laid eggs sequentially, as birds do, rather than all at once in a clutch, like crocodiles. But the dinosaurs still shared some traits with crocodiles: They nested in marshy areas, and their eggs were randomly spaced.
The reproductive systems of titanosaurs, the researchers conclude, were likely more similar to birds and crocodiles than to any other modern-day reptiles.
Experts note that it’s difficult to tell whether these 92 nests were all active at the same time or just created in the same vicinity over the course of decades, centuries or millennia.
Regardless, the find is astonishing, Zelenitsky tells Live Science’s Joshua A. Krisch in an email. “Frankly, it is surprising that discoveries of this magnitude are still being made.”