A newly discovered fossil has given scientists a rare chance to examine a marine reptile's live birth, captured perfectly in time.

According to BBC News, the fossilized Chaohusaurus was found with the remains of three babies. The young reptiles positions suggested that the creatures evolved on land and not in water.

"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," co-author of the study published in the journal PLOS One Dr. Ryosuke Motani, of the University of California, Davis, told BBC News.

The fossil was discovered in the central region of China's Anhui Province. The Chaohusaurus was one of the earliest marine reptiles and lived around 248 million years ago.

The fossil depicts the mother's tail extending to the right, her ribs to the left and her pelvis and hind flipper in the middle. Two embryos are visible - one inside the mother and one exiting her pelvis - while a third newborn's remains were found beneath her tail.

"The slab was collected for a fish called Saurichthys that was partly exposed in the field. We later realized that there was Chaohusaurus with babies on the same slab," said Motani.

The study researchers noted that the babies were born headfirst, as opposed to most marine live births that are tail first. Giving birth headfirst is completely normal for land-based animals.

"We always assumed that live-bearing in marine reptiles evolved after they invaded the sea, partly because of this difference. Now the new fossil shows that the most primitive marine reptile gave birth head first," said Motani. "This strongly suggests that they inherited live-bearing from their land ancestors."

The fossil is believed to be the oldest fossilized embryos of a Mesozoic marine reptile, about 10 million years older than the oldest on record.

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