Dr Stephan Lautenschlager has written a piece for The Conversation, in which he discusses recent compelling evidence that a species of archosauromorphs previously thought to venture onto land to lay eggs, gave birth to live young. The group of animals known as Archosauromorpha includes crocodiles, birds and their ancestors the dinosaurs.
'Giving birth to live young is one of the traits we use to distinguish mammals from other animals. But certain kinds of lizards, snakes and amphibians, both living and extinct, also reproduce without laying eggs. In fact, live birth (or viviparity) has evolved more than 100 separate times in non-mammal species throughout history. It seems to have been a common reproductive strategy in particular for extinct aquatic reptiles, such as the fish-like ichthyosaurs, plesiosaurs and mosasaurs that lived at the same time as the dinosaurs.
But one group of animals known as Archosauromorpha, which include crocodiles, birds and their ancestors the dinosaurs, has never been known to give birth – until now. A recently unearthed fossil, described in a new study by a team of scientists from China, the US, UK and Australia, shows that an ancient species of archosauromorph was giving birth around 245m years ago.'...