Did dinosaurs make good parents?
Ask that question several decades ago and you would have heard a resounding “no” from most palaeontologists. Back then, the “terrible lizards” were still seen as one-dimensional, scaly monsters. But our understanding of dinosaurs and their behaviour has changed much through a plethora of discoveries made around the world.
In the late 1970s, palaeontologist Jack Horner discovered Maiasaura – a duck-billed dinosaur which was the first recorded to exhibit feeding and care-taking of hatchlings. The animal’s scientific name means “good mother lizard.”
As consensus developed in the 1980s and ‘90s that modern birds are descended from the dinosaurs that weren’t killed off in a mass extinction 66 million years ago, it provided further verification that dinosaurs probably were caring parents. Birds today are known for paying close attention to their young and it makes sense that they inherited this behaviour from their ancestors.
But it seems there remain exceptions to the rule, and not all dinosaurs were built for parenthood.
A fossilised nesting site dating back to the last part of the Cretaceous period known as the Maastrichtian (66 to 72 million years ago) was found in the Narmada Valley in central India. The discovery is detailed in a paper published in the journal PLOS ONE.
“Together with dinosaur nests from Jabalpur in the upper Narmada Valley in the east, and those from Balasinor in the west, the new nesting sites from Dhar District in Madhya Pradesh (Central India), covering an east-west stretch of about 1000 km, constitute one of the largest dinosaur hatcheries in the world,” says co-author Guntupalli V.R. Prasad from the University of New Delhi.
Among the 92 nests were a total of 256 fossil eggs from gigantic titanosaurs.
The titanosaurs were the largest of the dinosaurs, and the largest land animals of all time. The long-necked, long-tailed herbivores belong to the sauropod group of dinosaurs. The largest species are believed to have measured nearly 40 metres in length and between 70 and 100 tonnes.
Until recent decades, the vast bulk of dinosaur discoveries came from Europe and North America.
Now, India, China, Australia, Africa and South America have emerged as hotspots for palaeontological study and finds are being reported with increased frequency. Having said that, the earliest record of titanosaurs anywhere came out of India in 1877. More giant sauropods have been found in India in recent years.
Bruhathkayosaurus is a titanosaur first described in 1987. The massive animal lived in India around 70 million years ago, and is estimated to have weighed up to about 80 tonnes and about 35 metres long at adulthood.
It’s not exactly clear which species laid the eggs found in the Narmada Valley. But palaeontologists have identified six different egg-species (oospecies), which is more than the number of titanosaur species known in the region from skeletal fossils.
Dinosaur reproductive habits can be difficult to determine. The Indian nesting ground provides a wealth of new data and insights into how the largest dinosaurs lived and reproduced.
The layout of the nests suggests that the titanosaurs buried their eggs in shallow pits, like crocodiles today.
Rare abnormalities such as the discovery of an “egg-in-egg” case indicate these sauropods had a reproductive system similar to modern birds, possibly laying their eggs sequentially like birds do today.
Read more: Chinese dinosaur egg fossils suggest dinos were in decline before asteroid impact caused their extinction
Also like birds, the fact that many nests are present in the same area reflects colonial nesting behaviour.
But titanosaurs aren’t small. They are, by definition, big. So the lack of space between the nests suggests that the mothers would lay the eggs and move on – leaving their hatchlings to fend for themselves.
“Our research has revealed the presence of an extensive hatchery of titanosaur sauropod dinosaurs in the study area and offers new insights into the conditions of nest preservation and reproductive strategies of titanosaur sauropod dinosaurs just before they went extinct,” says lead author Harsha Dhiman from the University of Delhi.
Fossil nesting sites of giant sauropods have previously been found in Brazil, Europe and, most famously, Argentina. These finds have also previously suggested a less than maternal instinct among titanosaurs.
But the latest discovery in India adds another dimension to the world’s largest dinosaurs.