This Ancient Reptile Gave Birth to Live Offspring

Roughly 245 million years ago, the long-necked Dinocephalosaurus dominated the China Sea. Nearly the size of a Siberian tiger, these creatures swept through the oceans long before dinosaurs roamed the earth.

Scientists have long thought that these creatures all laid eggs like their modern birds and crocodile relatives. But as Ben Guarino reports for the Washington Post, a new study suggests that Dinocephalosaurus went about babies a different way: They gave birth to live offspring.

The study, published in the journal Nature Communications, documents a puzzling fossil that researchers discovered in China’s Luoping Biota National Geopark—a site that is home to many exceptionally well-preserved specimen. Researchers, however, were initially unsure what they had, reports Guarino.

“I was not sure if the embryonic specimen was the last lunch of the mother or its unborn baby,” Jun Liu, a paleontologist at the Hefei University of Technology in China, told Guarino. “Upon closer inspection and searching the literature, I realized that something unusual had been discovered.”

Upon inspection the scientists discovered that they had found a baby dino still inside its mama. But to confirm the find was no easy task with the scant number of bones available, reports Guarino.

The scientists used the structure of the skeleton to confirm the tiny dino and massive creature were the same species. It’s unlikely that they were vaguely similar species because, according to Liu and his team, as far as scientists know, none existed at the time in the China Sea. They estimated that the smaller animal is about 12 percent the size of the adult.

Using the position of the smaller animal, writes Paul Rincon at the BBC, Liu and his team also ruled out that the smaller fossil was Dinocephalosaurus’ last meal. Predators normally swallow their prey headfirst, which helps the  prey travel down to the stomach more easily. As a result, meals face backwards within the stomach of animals. However, the smaller animal was facing forwards within Dinocephalosaurus.

The crucial piece of the puzzle was the posture of the embryo: It was in a curled position. This is the typical situation for vertebrates, Liu tells Guarino.

It’s still possible that the embryo was encased within an egg, and that the shell didn’t survive, says paper co-author Mike Benton from the University of Bristol to Rincon. But with the advanced development of the embryo, the team concluded that the live birth was most likely.

This discovery has wide-ranging implications for the entire Archosauromorpha family, of which Dinocephalosaurus is a member. Scientists will be studying both new fossils and old for more evidence that live birth was possible for multiple members of the species.