A remarkable fossil discovery is reshaping what scientists know about the early ancestors of mammals. Researchers have uncovered the fossil of a curled embryo belonging to Lystrosaurus, dating back around 250 million years, providing the first clear evidence that these ancient creatures reproduced by laying eggs.

The fossil was found in South Africa and analyzed using advanced imaging techniques, including high-resolution scans and powerful X-ray technology. What stood out to scientists was the structure of the embryo’s jaw, which had not yet fully fused — a feature seen today only in the embryos of egg-laying animals like birds and turtles.

This detail confirmed that the embryo had developed inside an egg, marking a major breakthrough in understanding how early mammal relatives reproduced.

Beyond reproduction, the discovery also helps explain how Lystrosaurus managed to survive one of Earth’s most catastrophic events — the Great Dying, which wiped out about 90% of life on the planet.

Scientists believe that laying relatively large eggs with soft, leathery shells may have given this species a survival advantage. These eggs likely retained moisture better in the harsh, dry environments that followed the extinction event, helping the species endure extreme conditions.

Additionally, the size of the eggs suggests that hatchlings were more developed at birth, allowing them to move, feed, and escape predators more effectively — increasing their chances of survival.

The findings also offer clues about the evolution of key mammalian traits, including lactation. Researchers suggest that milk production may not have originally evolved to feed offspring, but rather to keep eggs moist and protected before live birth became common.

Experts say this discovery fills an important gap in the story of how mammals evolved from reptile-like ancestors into the diverse group of animals we know today.