236-million-year-old fossil suggests live birth in mammals evolved 95 million years earlier

A fossilized cynodont dating to 236 million years ago shows a neonatal growth line and an unusually large birth size closely matching patterns seen in modern mammals, suggesting it gave birth to live young. The discovery could push the evolution of live birth in mammals back by up to 95 million years. It also raises the possibility that many traits considered distinctively mammalian evolved far earlier than previously thought.

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