For the first time in history, a team of international researchers has found evidence of live births in Archosauromorpha, the group that includes dinosaurs, crocodiles, and birds.
Until now, all animals found within the classification laid eggs. This led researchers to believe that something in their biology prevented live births. However, a recently discovered fossil suggests otherwise.
Researchers found the ancient lizard — known as a Dinocephalosaurus — in Luoping County, China, in 2008. The species was an aquatic reptile with a long neck that lived roughly 254 million years ago. The remains are interesting because the specimen had an embryo inside it when it died.
Such a discovery is so unexpected for this type of animal that researchers first believed the smaller reptile may have just been the creature’s last meal. However, it is facing forward and most swallowed prey faces the opposite direction. In addition, the smaller animal is the same species as the larger one.
“We were not sure if the embryonic specimen was the mother’s last lunch or its unborn baby,” said lead author Jun Liu, a Professor at the Hefei University of Technology in China, in a statement. “Upon further preparation and closer inspection, we discovered something unusual.”
This discovery pushes back the timeline on Archosauromorph reproductive biology by 50 million years and reveals that, like mammals and birds, Dinocephalosaurus determined the sex of their offspring genetically, BBC News reports. Both live birth and genotypic sex determination were necessary for animals like Dinocephalosaurus to become aquatic.
Now that researchers know there is no fundamental biological barrier within Archosauromorpha, they plan to closely examine other fossils to see if live birth is present somewhere else. They next will look at the relatives of aquatic crocodiles because little is known about their reproduction process.
“We identified that Dinocephalosaurus, a distant ancestor of crocodiles, determined the sex of its babies genetically, like mammals and birds,” added study co-author Chris Organ, a professor at Montana State University.”This new specimen from China rewrites our understanding of the evolution of reproductive systems.”
The findings are covered in a new study published in the journal Nature Communications.