This 250-million-year-old fossil proves mammal ancestors laid eggs
CNN • • science
Key Points:
- Researchers discovered the first definitive evidence that mammal ancestors, specifically Lystrosaurus from 250 million years ago, laid eggs, based on an embryo fossil found in South Africa.
- The embryo's unfused jaws, a trait shared only with modern bird and turtle embryos, indicate it developed inside a soft-shelled egg, which likely helped Lystrosaurus survive the harsh conditions following the Permian mass extinction.
- Large, leathery eggs would have reduced water loss and produced relatively mature hatchlings capable of early independence and faster reproduction, providing a survival advantage in dry environments.
- The study suggests lactation in mammals likely evolved between the early and late Triassic period, initially serving to keep eggs moist rather than to nourish offspring.
- Further research is planned to explore the evolution of lactation and live birth, key traits that define mammals, with experts noting this discovery clarifies the reproductive transition from reptile-like ancestors to modern mammals.
