What this evidence of live birth from a 250-million-year-old fossil of the long-necked relative of dinosaurs found in China tells us?

More than an evidence of live birth, the discovery has its profound effect on the present knowledge about the reproductive biology among Archosauromorphs.

The fish-eating Dinocephalosaurus fossil, an archosauromorp, thrived during the Middle Triassic Period in the shallow regions of South China Sea.

The researchers were "excited" when they discovered the pregnant fossil, according to Prof. Jun Liu, lead researcher from Hefei University of Technology in China.

The animal may have been three to four meters long with a neck that is about 1.7 meters long.

Reproductive Biology Re-written

"Live birth is well-known in mammals, where the mother has a placenta to nourish the developing embryo" Prof. Jonathan Aitchison, head of the University of Queensland School of Earth and Environmental Sciences, said.

This mode of reproduction, however, has not been known among the third major group of living land vertebrate, crocodiles, and birds until recently.

The evolution of live birth happens independently among mammals and bigger groups of lizards and snakes, based on an article published in Nature Communications on Feb. 14. However, it was not known among Archosauromorphs, represented today by crocodiles and birds.

Live birth — technically known as viviparity — among scaled reptiles has evolved at least 115 times despite the complex process of the transition. This transition from egg-laying — or oviparity — to live birth involved the changes of the mother's form and structure, internal organs, and behavior leading to the feeding of embryo by the mother through a placenta.

It was thought that live birth was common only among lizards and snakes but not among the wider group living land vertebrate composed of crocodiles and birds.

Not until the discovery of the pregnant fossil. The embryo, measured about half a meter long, was inside the rib cage of the adult Dinocephalosaurus fossil.

At first, the researchers were not certain if the smaller fossil was the animal's last meal or unborn baby. Upon closer inspection and analysis, it was established that the fossil inside the adult animal was indeed the unborn baby.

Genetic Sex Determination

Professor Chris Organ, a fellow researcher from Montana State University, said analysis of the evolution had shown the live birth, in this case, was due to genetic sex determination.

"Some reptiles today, such as crocodiles, determine the sex of their offspring by the temperature inside the nest," he said.

The recent findings have shown that "Dinocephalosaurus, a distant ancestor of crocodiles, determined the sex of its babies genetically, like mammals and birds."

Liu said the discovery "pushes back evidence of reproductive biology among Archosauromorphs" by around 50 million years.

The discovery of the 250-million-year-old fossil has furnished "information on reproductive biology of archosauromorphs before the Jurassic Period," Liu said 

Importance Of The Discovered Fossil

Archosauromorphs was one of the three large groups of land-based vertebrates. Each of the three groups numbered around 10,000 species.

The recent finding shows that the long-necked animal could achieve live birth.

Prof Mike Benton, co-author from the University of Bristol, told BBC News that palaeontologists would now be "looking very closely" at other fossils of animal group whose information on how they reproduction is not yet known.

One target is the group of aquatic crocodile, Benton said.

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