Researchers have uncovered 92 nesting sites containing a total of 256 fossil eggs belonging to India’s largest dinosaurs, in the Lameta Formation, Narmada Valley, Madhya Pradesh. The discovery of these fossilised eggs reveals intimate details about the lives of titanosaurs in the Indian subcontinent.
All about titanosaurs
Titanosaurs were a diverse group of sauropod (characterised by a large size, long neck and tail, four-legged stance and a herbivorous diet, and were the largest of all dinosaurs) dinosaurs which lived from the Late Jurassic Epoch (163.5 million to 145 million years ago) to the end of the Cretaceous Period (145 million to 66 million years ago), and were the largest terrestrial animals known to have walked the surface of Earth. Some titanosaurs were as big as modern whales. About 40 species of titanosaurs have been identified, with fossils discovered in all continents except Antarctica.
Titanosaurs were herbivorous quadrupeds with long tails, long necks and small heads, and possessed vertebrae with a honeycomb-like internal structure.
The study, led by Harsha Dhiman of the University of Delhi, was published January 18 in the journal PLOS ONE.
Titanosaur fossils were discovered in Lameta Formation of Madhya Pradesh
The Lameta Formation located in central India is well-known for fossils of dinosaur skeletons of the Late Cretaceous Period, which occurred from 100.5 to 66 million years ago. Dhiman and colleagues discovered these fossils during recent work in the Lameta Formation. Through detailed examination of the nests, Dhiman and colleagues have made inferences about the life habits of titanosaurs that lived in India during the Late Cretaceous.
How many egg species were identified?
As many as six different egg species, called oospecies, were identified. This suggests a higher diversity of titanosaurs than is represented by skeletal remains from the region.
How did the dinosaurs bury their eggs?
The dinosaurs buried their eggs in shallow pits like modern-day crocodiles, the layout of the nests reveals. A rare case of an “egg-in-egg” was also seen in one of the titanosaur eggs. This, along with certain pathologies found in the eggs, indicate that titanosaur sauropods had a reproductive physiology that parallels that of birds. There is also a possibility that titanosaur sauropods laid their eggs in a sequential manner as seen in modern birds.
Reproductive patterns observed
The researchers have also been able to understand the reproductive biology of titanosaurs, such as the possibility of segmented oviduct and sequential laying of eggs by titanosaurs.
The number of eggs laid by an organism during a single reproductive event is called a clutch.
Clutch patterns seen
The researchers found three clutch patterns, namely circular, combination and linear.
The researchers also attempted to infer aspects such as egg burial, absence of parental care and colonial nesting behaviour.
In which lithologies were the eggs found?
The eggs were found within sandy limestone and calcareous sandstone lithologies (rock compositions). The researchers found ferruginous (containing oxides or rust) sandstone in the Jamniapura and Padlya regions of Dhar District, indicating the possibility of an alluvial or a fluvial setting, which refers to a region with materials deposited by moving water bodies.
What does the presence of several nests in the same area indicate?
Several nests were found in the same area, suggesting that these dinosaurs exhibited colonial nesting behaviour like many modern birds, the study said. However, the nests were closely spaced, indicating that little room was left for adult dinosaurs. This supports the idea that the adult dinosaurs left the hatchlings to fend for themselves.
It can be difficult to determine details of dinosaur reproductive habits. The fossil nests, which come from a time shortly before the age of dinosaurs came to an end, provide a wealth of data about some of the largest dinosaurs in history. The findings improve palaeontologists’ understanding of how dinosaurs lived and evolved.
Significance of the study
The Upper Cretaceous or Maastrichtian Lameta Formation is well-known for its osteological (relating to bones) and oological remains of sauropods from the eastern and western parts of the Narmada Valley, and the newly documented 92 titanosaur clutches from the Dhar District of Madhya Pradesh add further to the extensive data, the study said.
Some egg clutches were laid close to lake or pond margins, while most were laid away from lake and pond margins, the authors noted in the paper.
The findings will help researchers understand more about titanosaur palaeobiology. The researchers found some unhatched eggs, which indicate infertility, death of embryos prior to hatching, deep burial of eggs, environmental factors such as floods, or being laid close to lakes and ponds.
The eggs that were laid in soft, marshy sediments associated with small lake or pond bodies would occasionally get submerged, thus remaining unhatched. Moreover, frequent exposure resulted in desiccation and shrinkage cracks, and submergence caused sediments to cover the clutches.
Most of the eggs were hatched in the Akhada and Dholiya Raipuriya regions of Dhar District.
There is a greater number of hatched eggs compared to unhatched eggs, indicating that few clutches occurred close to lakes or pond margins in Jhaba and Padlya regions, while most clutches occurred away from the lake or pond margins, and hence, were hatched, the authors concluded.