Ancient Cynodont Fossil Pushes Live Birth Deep into Mammal Lineage
Analysis of a 236-million-year-old cynodont fossil from Argentina reveals a neonatal bone line indicating live birth, with a newborn mass around 1.68 kg (about 10–20% of an adult), suggesting viviparity originated in the mammalian lineage far earlier than thought (roughly 90–95 million years ago) and proposing two plausible evolutionary scenarios for this trait's emergence.