‘Abnormal’ Dinosaur Egg Discovered In Madhya Pradesh. Know Its Connection With Crocodiles, Birds

An "abnormal" dinosaur egg in the form of an egg with another egg has been discovered in Madhya Pradesh. The discovery marks the first report of egg pathology in dinosaurs.

Field photographs of eggshells belonging to a titanosaur ( Image Source :Scientific Reports )

An "abnormal" dinosaur egg in the form of an egg with another egg has been discovered in Madhya Pradesh, a state in western Central India. The egg, also called a pathologic egg, occurs in the form of an egg within another egg, a condition known as ovum-in-ovo. Pathologic eggs can also occur in the form of multi-shelled eggs showing additional pathological eggshell layer (s) along with the primary shell layer, and have been documented in the amniote eggs of birds, turtles, and dinosaurs. An amniote egg is an air-breathing egg characterised by a shell and extraembryonic membranes, which enclose the amniote embryo in a private pond during its development.

How Is The Discovery Special?

Though multi-shelled eggs and eggshells were previously recorded only in reptiles and ovum-in-ovo eggs in birds, it has now been shown that multi-shelled pathology can be found in birds also. However, no ovum-in-ovo egg had been reported in dinosaurs or other reptiles, until now. 

The new study, led by researchers at the University of Delhi, describes an ovum-in-ovo pathological egg from a titanosaurid dinosaur nest from the Upper Cretaceous Lameta Formation of western Central India. The paper was recently published in the journal Scientific Reports. The discovery marks the first report of egg pathology in dinosaurs.

What Are Titanosaurs?

Titanosaurs are a diverse group of sauropod 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). Sauropods were marked by large size, a long neck and tail, a four-legged stance, and a herbivorous diet. These reptiles were the largest of all dinosaurs and the largest land animals that ever lived.

Titanosaurs, like other sauropods, were herbivorous quadrupeds with long tails, long neck, and small heads, but differed from other sauropods in that the titanosaurs' bodies were stockier.

Oviduct Morphology Of Dinosaurs Was Similar To That Of Birds

Birds have a specialised uterus while other amniotes have a generalised uterus. Amniotes are vertebrates which undergo foetal development within an amnion. Meanwhile, alligators and crocodiles retain a specialised uterus like birds, and also a reptilian mode of egg-laying. According to the study, the discovery of an ovum-in-ovo egg from a titanosaurid dinosaur nest suggests that the oviduct morphology of the dinosaurs was similar to that of birds. This indicates there is a possibility that sequential laying of eggs occurred in this group of sauropod dinosaurs. 

The researcher discovered 52 nests, and out of these, only one pathological egg was documented. According to the study, the abnormalities reflected in the eggshells include multiple eggshell units occurring in close contact with each other and one above the other, known as multi-shelled eggs, abnormally thick or thin eggshells, abnormally shaped shell units, extra shell units blocking pore canals, and surface defects.

Ovum-In-Ovo Pathology Is Not Unique To Birds

The new finding underscores the fact that ovum-in-ovo pathology is not unique to birds and sauropods share a reproductive behaviour very similar to that of other archosaurs. This is a large group of vertebrates that includes reptiles such as dinosaurs and pterosaurs, and is represented by modern-day birds and crocodilians. 

There are two traits which collectively characterise dinosaurs, birds, and other archosaurs. One trait is that these animals have an oviparous mode of reproduction, in which organisms are produced by laying eggs. Another trait is that dinosaurs, birds, and other archosaurs lay cleidoic eggs, which are eggs enclosed in a relatively impervious shell that reduces free exchange with the environment. Cleidoic eggs are instrumental in the rise of amniotes.

Sauropods Built Community Nests

According to the study, different egg macroscopic features and eggshell microstructures occur in different types of dinosaurs. For instance, spherical-shaped eggs were found in sauropods and elliptical-shaped eggs were found in theropods, which were carnivorous bipeds. 

Bird-like behaviour has also been observed in the fossil record of dinosaurs in the form of nest constructions and evidence of parental care, especially in derived theropods. Meanwhile, hadrosaurs and sauropods spent their time in building community nests. 

The cross-sectional outline of the unusually double-layered in-situ egg found in the Upper Cretaceous Lameta Formation of Padlya, Dhar District, Madhya Pradesh shows physical organisation of the two shell layers similar to the ovum-in-ovo eggs previously reported in birds.

Sauropods Had Reproductive Anatomy Similar To Those Of Archosaurs

In the paper, the researchers describe the newly found ovum-in-ovo pathological titanosaurid egg and discuss its preservation and relevance for understanding sauropod reproductive biology. The finding represents the first discovery of ovum-in-ovo pathology in dinosaurs. The researchers hypothesise that ovum-in-ovo pathology is not only unique to birds,and that sauropod dinosaurs had a reproductive anatomy similar to those of archosaurs such as crocodiles and birds. The reproductive anatomy of sauropod dinosaurs was not similar to that of non-archosaurian reptiles like turtles and lizards. 

The present discovery of an ovum-in-ovo pathological egg in a titanosaurid dinosaur nest is the first of its kind in dinosaurs and demonstrates its presence in reptiles as well, specifically in dinosaurs, the researchers conclude in the study. Moreover, the study underscores the fact that the reproductive biology of sauropods is more similar to that of archosaurs such as crocodiles and birds than to non-archosaurian reptiles.