Oldest fossil egg confirms mammal ancestors laid eggs about 250 million years ago
Researchers analyzed a 252–250 million-year-old Lystrosaurus fossil egg found in South Africa and, using synchrotron imaging at the ESRF, revealed a curled embryo whose jaw bones suggest it was still in an egg. This proves therapsids (the precursor to mammals) laid eggs (oviparous) rather than giving live birth, offering clues about embryo development, egg size, and survival strategies after the Great Dying. The large, leathery eggs likely reduced desiccation and supported precocial hatchlings, informing our understanding of early mammalian reproduction and the evolution of lactation.
