New Fossil Discovery Confirms Mammal Ancestors Laid Soft-Shelled Eggs

Wed, 15 Apr 2026 06:49:00 +0200

A groundbreaking fossil discovery in South Africa has resolved a long-standing question about early mammalian evolution. Researchers from the University of the Witwatersrand and the European Synchrotron Radiation Facility identified a 250-million-year-old egg containing a perfectly curled Lystrosaurus embryo — the first confirmed egg ever found from a mammal ancestor. Lystrosaurus, a resilient plant-eating therapsid that thrived after the catastrophic End-Permian Mass Extinction, is now known to have reproduced by laying soft-shelled eggs similar to those of modern reptiles and monotremes. Advanced synchrotron X-ray CT scanning allowed scientists to confirm that the embryo had not yet fused its lower jaw bones, indicating it died before hatching. The egg's soft and nutrient-rich structure explains why similar fossils are extremely rare, as these eggs decay quickly and seldom fossilize. The study reveals that Lystrosaurus produced relatively large eggs packed with yolk, enabling the hat