Scientists have their first proof that the ancestors of some mammals laid eggs, thanks to a 250-million-year-old fossil embryo discovered in South Africa in 2008. The specimen, described this week in PLOS One, belongs to a piglike animal with tusks and a beak called Lystrosaurus that famously and mysteriously survived the Great Dying, one of Earth’s worst extinction events. The embryo’s curved position and the incomplete development of its jaw, pelvis, and ribs hint that it was in an egg when it died (artist’s rendition above). The fossil could shed light on how Lystrosaurus survived the high temperatures of the extinction event, as the large size of the eggs would have prevented the water loss that comparable species faced, CNN reports. The find may also help researchers learn why and when lactation developed in mammals, providing evidence it initially evolved to allow mothers to keep their eggs moist.
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