Ancient mammal ancestors laid eggs, fossil reveals
A 250-million-year-old Lystrosaurus fossil preserves a soft-shelled egg and a tiny embryo, providing the first direct evidence that mammal ancestors laid eggs; synchrotron X-ray imaging revealed an unfused jaw and an embryo that likely died inside the egg, suggesting large yolk-rich eggs and precocial hatchlings aided survival after the End-Permian extinction and reshaped ideas about mammalian origins.