The fossil egg and embryo were discovered near Oviston in South Africa's Eastern Cape province in 2008 by palaeontologist John Nyaphuli and have been kept in the National Museum in Bloemfontein. It belongs to a species called Lystrosaurus, which lived 252 million to 250 million years ago and had adults resembling a pig with naked skin, a turtle-like beak, and two downward-pointing tusks. The fossil preserves no shell, with only a curled-up embryo visible; any shell was likely leathery or had dissolved over time.
Between 280 and 200 million years ago, therapsids evolved, eventually giving rise to mammals including humans. Therapsids were first described more than 150 years ago based on fossils from South Africa, and James Kitching, a South African fossil hunter, excavated many thousands from the Karoo region, finding fossilized dinosaur eggs but never therapsid eggs. Some mammals like platypuses and echidnas lay eggs, raising the question of whether therapsids laid eggs or were viviparous; only the most advanced dinosaurs laid hard-shelled eggs.
Advanced X-ray technology at the European Synchrotron Radiation Facility in Grenoble, France, was used to image the inside of the embryo's bones. The lower jaws of the embryo's beak were not completely fused, a developmental trait found in modern turtles and birds where jaw bones fuse before birth for beak strength. The curled-up Lystrosaurus embryo died in ovo, nestled in a soft, leathery eggshell, providing evidence that therapsids laid eggs. The exact age of the fossil within the 252-250 million year range and whether other therapsid species also laid eggs remain unknown, as does how the fossil was preserved without a shell and the full developmental stage of the embryo.