It is well established in evolutionary biology that mammals arose from within the synapsid lineage, the ancient group that includes the therapsids - stem-mammals that long predate true mammals. What had remained uncertain, however, was whether those early synapsids still reproduced by laying eggs, as modern monotremes such as the platypus and echidnas do, or whether live birth had evolved much earlier in the mammalian line.
That gap in our knowledge has now been narrowed dramatically and, no doubt to the acute discomfort of creationists, the evidence shows that about 250 million years ago - roughly 244 million years before young-Earth creationists believe the Earth was created - a therapsid was still reproducing by laying eggs. The evidence comes from a fossil embryo discovered in South Africa in 2008 by palaeontologist John Nyaphuli. Even more awkward for creationists, their mythology requires animals to have been created as separate, unrelated ‘kinds’, yet here we have direct evidence from the stem-mammal lineage showing a reproductive stage inherited from deep evolutionary ancestry rather than sudden, magical creation without predecessors.
Now Julien Benoit and Jennifer Botha of the University of the Witwatersrand, South Africa, together with Vincent Fernandez of the European Synchrotron Radiation Facility in Grenoble, France, have used high-resolution CT and synchrotron imaging to examine the curled-up embryo inside the rock and identify it as a young Lystrosaurus, a dicynodont therapsid from the Early Triassic. Crucially, the specimen preserves features consistent with an unhatched embryo, including a tightly curled in ovo posture and an unfused lower jaw symphysis. No calcified eggshell was preserved, so the egg was probably soft and leathery, as expected for a very early synapsid. Their findings are reported in an open access paper in PLOS One.
The authors have also co-authored an article in The Conversation explaining the discovery and its significance. Their article is reprinted here under a Creative Commons licence, reformatted for stylistic consistency.



































