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250-Million-Year-Old Fossil Egg Reveals Early Mammal Ancestors

4/16/2026

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Summary

Story summary

Researchers found a 250-million-year-old fossilized egg in South Africa with a curled-up Lystrosaurus embryo, marking the first evidence that mammal ancestors laid eggs.
The embryo's unfused jaw shows it had not hatched, suggesting it died inside a leathery-shelled egg.
The findings suggest this reproductive strategy helped Lystrosaurus survive the Permian-Triassic extinction and inform mammalian evolution and resilience to climate change.

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Story summary

Researchers found a 250-million-year-old fossilized egg in South Africa with a curled-up Lystrosaurus embryo, marking the first evidence that mammal ancestors laid eggs.
The embryo's unfused jaw shows it had not hatched, suggesting it died inside a leathery-shelled egg.
The findings suggest this reproductive strategy helped Lystrosaurus survive the Permian-Triassic extinction and inform mammalian evolution and resilience to climate change.