Ancient Reptile Live Birth Discovered in 248-Million-Year Old Fossil

Paleontologists in China have uncovered the earliest evidence of live birth from an ancient Mesozoic marine reptile, well preserved in a 248-million-year old fossil.

The newly discovered fossil specimen belongs to Chaohusaurus, the oldest Mesozoic marine reptile that existed some 248 million years ago. Entombed in the fossil is a well preserved maternal skeleton of Chaohusaurus, a genus of ichthyosaur, which apparently died while in labor. This fossil indicates that the sea predator birthed its young ones headfirst.

This finding was led by Ryosuke Motani from the University of California, Davis, and colleagues.

Listed as the top ocean predators, Ichthyosaurs existed when dinosaurs roamed the earth i.e. 250 million years ago. This giant marine reptile though looked like a fish with a dorsal fin and tail. They evolved from ancestral terrestrial reptiles. It was during the Triassic period (between 251 million-247 million years ago) that land reptiles moved to water.  These reptiles were abundant during the Jurassic period.

The partial skeleton in China confirms that these reptiles gave head-first birth to live offspring.

"Being reptiles, their ancestors lived on land. What happened during the transition from land to the sea is not well understood, and Chaohusaurus holds a key to [unlock] the mystery,"  Motani said to BBC.

Along with the maternal skeleton there are three embryos- one inside the mother, other in the process of being born with half of the body still inside the mother and the third newly born lying next to the mother. It is the second embryo with a headfirst birth posture, which clearly reveals the position of births in ichthyosaurs.

According to the researchers, based on the burial position, it is doubtful that the babies were expelled from the mother after death.

"The reason for this animal dying is likely difficulty in labor," Motani told LiveScience."Obviously, the mother had some complications,"

This is different from the other air breathing marine creatures like whales and dolphins that give birth to their babies with the tail coming out first. This birthing procedure avoids suffocation in newborns during labor. The earliest whales also evolved from land mammals and gave birth to their babies headfirst, reports LiveScience.

According to the news release, the new specimen is the oldest fossil embryo of Mesozoic marine reptile and is 10 million years older than what was previously believed.

Dr. Motani adds, "The study reports the oldest vertebrate fossil to capture the 'moment' of live-birth, with a baby emerging from the pelvis of its mother. The 248-million-year old fossil of an ichthyosaur suggests that live-bearing evolved on land and not in the sea."

The maternal skeleton was hidden along with another fossil belonging to the Saurichthys fish. The newly discovered specimen is currently housed at the Anhui Geological Museum in Hefei, China.

The finding was documented in the journal PLOS One.