Just out @ Science
Live birth in a new lineage
Live birth has evolved multiple times among vertebrates, most notably in mammals. Although live birth also occurs in some reptiles, including several extinct marine reptiles, it has appeared convincingly to be absent in the Archosauromorphs, the lineage leading to dinosaurs, birds, and crocodiles. Liu et al. describe a previously unknown marine Archosauromorph from the middle Triassic in China, Dinocephalosaurus, which shows evidence of an embryo within the body cavity. Viviparity in marine animals has clear functional advantages, but the lack of evidence for live birth across millions of years in this large group has caused some to question whether its evolution was impossible because of some genetic or developmental constraint. This new evidence suggests that, at least initially, this was not the case.
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