More than 250 titanosaur eggs have been uncovered in India, revealing more about the lives of some of the largest animals which ever lived.

Among the eggs was one containing the remains of a second egg inside it which suggests that these mighty sauropods may have reproduced similarly to modern birds.

There could have been more titanosaurs in India than previously thought.

A new study, published in the journal PLOS ONE, found evidence of six different types of fossilised egg across the Lameta Formation in central India. They date to the Late Cretaceous, and are thought to have been buried by lava during the eruption of a volcanic area known as the Deccan Traps.

While these eggs don’t necessarily all come from different dinosaur species, it adds weight to theories that there could have been more titanosaurs living in India than the three types that are currently known.

Professor Guntupalli V.R. Prasad, co-author and leader of the research team, says, ‘Together with dinosaur nests from Jabalpur in the east and Balasinor in the west, the new nesting sites from Madhya Pradesh’s Dhar District cover an east-west stretch of about 1000 kilometres.’

‘This constitutes one of the largest dinosaur hatcheries in the world.’

Titanosaur reproduction

Titanosaurs are among the largest animals which have ever walked the Earth. While they had a similar appearance to other sauropods, such as Diplodocus, they were much bigger.

One of the largest species, Patagotitan mayorum, is believed to have measured over 37 metres long, or the same length as two bowling lanes.

While titanosaur remains are found all over the world, they are most species rich in South America. Around 75% of all titanosaur species are known from Patagonia, with the Auca Mahuevo site having been particularly important for understanding how these dinosaurs reproduced.

Spectacularly preserved sites such as these have revealed exquisite fossils, such as a preserved titanosaur embryo. Described in 2020, this fossil revealed that, like modern birds, titanosaurs developed an egg tooth they used to break open the shell when they were ready to hatch.

But because preserved eggs are very rare, it is difficult for researchers to directly link a type of egg to a type of dinosaur.

Dr Susannah Maidment, a Principal Researcher and Curator of Dinosaurs at the Museum, explains, ‘Dinosaur eggs aren’t very common in the fossil record, and this may be because of how they evolved. A recent paper suggested that some ornithischians, a group of dinosaurs containing ankylosaurs, stegosaurs and Triceratops, may have had soft shelled eggs.’

‘It’s possible that the ancestors of this group, and perhaps even dinosaurs as a whole, didn’t have hard eggshells. However, it’s hard to tell if ornithischians lost their ability to make hard eggs, or if other dinosaurs such as the sauropods and theropods gained it.’

The newly discovered nesting sites in India help to add further evidence for researchers investigating the process of dinosaur reproduction.

Inside a titanosaur nesting colony

Across the Dhar District, the researchers excavated 92 nests as part of the study. These mounds of earth were likely dug from the soft sediment of a floodplain environment over 66 million years ago.

The nests were packed closely together, suggesting that while the dinosaurs may have laid their eggs together in colonies, the parents may not have stuck around to look after them.

‘We think that sauropods like the titanosaurs lived in herds because of their preserved footprints and trackways, and it seems that they also nested together as well, like some birds,’ Susie says. ‘Their strategy of laying a lot of eggs packed densely together is not one commonly associated with parental care.’

‘While there are fossils of some dinosaurs, such as the meat-eating theropods, where parents are preserved sitting on a nest, there is no evidence of that kind of behaviour in the sauropods. It looks like sauropods laid their eggs and then left their offspring to fend for themselves.’

Though the parents may have left, the eggs would still need to be kept warm during their incubation period. Whether this was by burying them under sand like turtles, or under rotting plant material like crocodiles, is still debated by scientists.

A lack of preserved plant material and the pattern of fragmented eggshell at the Indian nests have led the researchers to suggest that burial under sand may have been more likely, at least in titanosaur species such as Jainosaurus and Isisaurus which once lived on the subcontinent.

While the results seem to suggest that these eggs were part of a nesting colony, other explanations can’t be completely ruled out. More research will be needed to confirm whether the different nests were made at the same time.

A unique dinosaur egg

Among the 256 eggs found at the site, one in particular caught the researchers’ attention.

It appears to show a layer of eggshell inside another egg, with its shape suggesting that it had always been this way.

While multi-shelled eggs, where an egg can have more than one external layer, are not uncommon in birds, reptiles and dinosaurs, the researchers believed this fossil was something different.

They think it is an ovum-in-ovo egg, where one egg is found inside another. If confirmed, it would be the first example of an ovum-in-ovo egg not only in dinosaurs, but reptiles as a whole.

Currently these eggs are only known of in birds, where they form under stressful conditions such as disease, lack of food or abnormal temperatures. This causes a developing egg to be pushed back into the mother’s body after its shell has started forming.

When this egg meets a less developed egg, it can be covered in another layer of yolk and albumen before being shelled again. This is possible because different sections of a bird’s oviduct carry out different roles, causing the egg to repeat certain stages of its formation.

As birds are descended from dinosaurs, it suggests that titanosaurs and their ancestors may have had a similar reproductive system. Discovering exactly when this ability evolved would help to support or refute this theory, and tell us more about how dinosaurs might have behaved.