Viviparity, the form of birth that produces living young, and not external eggs, could date back to 280 million years ago or even earlier, a new study has suggested.
It means that humans were not the first to evolve it.
The study focuses on mesosaurs, which were among the world's first aquatic reptiles. They lived in what are now South America and South Africa at a time when these two landmasses were united and part of the giant supercontinent Pangaea.
Mesosaurs, and even their earlier ancestors, possibly "were not able to produce hard shelled eggs, at least for the first several million years of their evolution," lead author Graciela Pineiro, a paleontologist at Uruguay's Facultad de Ciencias, told Discovery News.
"After the recent discovery of mesosaur embryos, we can state with a high degree of confidence that embryo retention developed early in amniote evolution, given that mesosaurs are among the basal-most reptiles and that they date from the Early Permian around 280 million years ago," she asserted.
Pineiro and colleagues Jorge Ferigolo, Melitta Meneghel and Michel Laurin recently discovered the exceptionally well-preserved mesosaur embryos at sites in Uruguay and Brazil. The environmental conditions at the locations allowed for the preservation of soft tissues, nerves and blood vessels, she said.
There is also compelling evidence that giant, carnivorous, four-flippered reptiles known as plesiosaurs gave birth to live young as well.
Robin O'Keefe of Marshall University and team discovered a big embryonic marine reptile contained in the fossil of its 15.4-foot-long mother, which lived 78 million years ago.
The new findings were published in the December issue of Historical Biology: An International Journal of Paleobiology. (ANI)