Producing living young, and not external eggs, is a form of
birth that could date back to 280 million years ago or even
earlier, a new study suggests. Called viviparity, this form of
birth is used by humans, but clearly we were far from being the
first to evolve it. The study, published in the December issue
of Historical Biology: An International Journal of Paleobiology,
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 Piñeiro, 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,