250-million-year-old fossil proves that mammal ancestors laid eggs
The little skeleton was curled so tightly it looked as if it had never really entered the world. For years, that mattered because paleontologists suspected they were looking at something unusual, a baby Lystrosaurus that may have died before hatching. But suspicion is not proof, and this question had lingered for decades, not just for this fossil, but for a much bigger mystery in evolution. Did the ancestors of mammals lay eggs? A new analysis of a tiny Lystrosaurus specimen from South Africa now gives the clearest answer yet: yes, they did. The fossil, dating to roughly 250 million years ago, appears to preserve an embryo still inside its egg, making it the first known egg from a mammal ancestor. That matters because Lystrosaurus was no obscure reptile-like relic. It was one of the great survivors of the end-Permian mass extinction, the catastrophe about 252 million years ago that wiped out vast numbers of species. In the brutal aftermath, with heat, drought, and ecological collapse reshaping life on land, Lystrosaurus did not merely persist. It …
