Researchers analyzed a 250-million-year-old Lystrosaurus fossil embryo using advanced CT imaging and found the first direct evidence that mammal ancestors laid eggs, answering a decades-old paleontological question. The discovery suggests that large, leathery eggs may have helped this species survive Earth's worst mass extinction 252 million years ago by resisting desiccation during extreme drought conditions. The fossil was found in South Africa and shows an embryo still inside its shell with an unfused lower jaw — a key indicator the animal died before hatching. This research has implications for understanding how modern species might adapt to environmental stress from climate change.