First-Ever Egg of a Mammal Ancestor Has Been Discovered by Wits Professors!

Two Wits professors, alongside an international team, have answered one of palaeontology’s longest-running questions! Did mammal ancestors lay eggs? Johannesburg, South Africa (10 April 2026) – Scientists have made... The post First-Ever Egg of a Mammal Ancestor Has Been Discovered by Wits Professors! appeared first on Good Things Guy.

Apr 10, 2026 - 12:40

First-Ever Egg of a Mammal Ancestor Has Been Discovered by Wits Professors!

Two Wits professors, alongside an international team, have answered one of palaeontology’s longest-running questions! Did mammal ancestors lay eggs?

Johannesburg, South Africa (10 April 2026) – Scientists have made a jaw-dropping discovery of the very first egg ever found from a mammal ancestor! The breakthrough centres on the Lystrosaurus, a distant ancestor of modern mammals that survived the worst mass extinction our planet has ever seen.

About 252 million years ago, Earth went through its darkest chapter. The End-Permian Mass Extinction, often called ‘The Great Dying’, wiped out the vast majority of all species on the planet. Volcanic eruptions, extreme heat, and long droughts made conditions nearly impossible for life back then.

Lystrosaurus, on the other hand – a stocky, plant-eating creature roughly the size of a pig – somehow survived, and actually thrived.

For decades, scientists have puzzled over how it managed this. Now a groundbreaking study published in the journal PLoS ONE has finally provided a key piece of the answer that was hidden inside a fossilised egg.

An international team led by Professor Julien Benoit and Professor Jennifer Botha of the Evolutionary Studies Institute at the University of the Witwatersrand in Johannesburg, along with Dr Vincent Fernandez of the European Synchrotron Radiation Facility in France, have confirmed the existence of a Lystrosaurus egg containing an embryo dating back approximately 250 million years.

This is the first time in history that an egg from a mammal ancestor has ever been conclusively identified.

Lystrosaurus embryo within its partially preserved shell, photograph of the fossil. Supplied by GENUS, University of the Witwatersrand.

The story began almost two decades ago in 2008, during a field expedition led by Professor Botha.

“This fossil was discovered during a field excursion I led in 2008, nearly 17 years ago. My preparator and exceptional fossil finder, John Nyaphuli, identified a small nodule that at first revealed only tiny flecks of bone. As he carefully prepared the specimen, it became clear that it was a perfectly curled-up Lystrosaurus hatchling. I suspected even then that it had died within the egg, but at the time, we simply didn’t have the technology to confirm it,” says Professor Botha.

The fossil sat with its secret locked inside until modern technology could catch up, and it finally did when the team used a synchrotron, which is essentially an enormously powerful X-ray machine, at the European Synchrotron Radiation Facility in France.

This tech can scan ancient fossils in extraordinary detail without damaging them, revealing even the tiniest structures inside.

“Understanding reproduction in mammal ancestors has been a long-lasting enigma and this fossil provides a key piece to this puzzle. It was essential that we scanned the fossil just right to capture the level of detail needed to resolve such tiny, delicate bones.” says Dr Fernandez describing the thrilling discovery.

The scans revealed a critical clue that the baby’s lower jaw had not yet fused together. In animals, the lower jaw is made up of two halves that must join before the creature can eat, meaning this individual would have been completely incapable of feeding itself.

“When I saw the incomplete mandibular symphysis, I was genuinely excited,” says Professor Benoit. “The mandible, the lower jaw, is made up of two halves that must fuse before the animal can feed. The fact that this fusion had not yet occurred shows that the individual would have been incapable of feeding itself.”

What this means, in other words, is that this tiny creature had never eaten a meal. Despite no eggshell being preserved in the fossil, the jaw development confirmed the creature had died before hatching, still inside the egg.

CT scan of the skeletal elements. Supplied by GENUS, University of the Witwatersrand.

These eggs were likely soft-shelled, more like the eggs of some modern reptiles than the hard-shelled eggs of dinosaurs. That’s why they’re so rare as fossils. Soft shells don’t preserve well, meaning this find confirms something exceptionally extraordinary.

The fact that mammal ancestors did, in fact, lay eggs is the headline answer to a question scientists have debated for over 150 years.

It gets even more fascinating. The research suggests that Lystrosaurus laid large eggs relative to its body size. Larger eggs contain more yolk, a nutrient-rich food source that feeds a developing embryo. This means the babies could grow and develop fully inside the egg, without needing their mother to feed them after hatching.

This tells us two more important things. One, that Lystrosaurus almost certainly did not produce milk for its young, unlike modern mammals. And two, that the hatchlings were likely precocial, meaning they were born at an advanced stage of development, ready to fend for themselves almost immediately after hatching.

The discovery provides the first direct evidence of egg-laying in mammal ancestors and also offers an explanation for how the Lystrosaurus came to thrive.

Reconstruction of the animal. Supplied by GENUS, University of the Witwatersrand.

Professor Botha reflects on a discovery nearly two decades in the making.

“What makes this work especially exciting is that we were able to quite literally follow in John Nyaphuli’s footsteps, returning to a specimen he discovered nearly two decades ago and finally solve the puzzle he uncovered. At the time, all we had was a beautifully curled embryo, but no preserved eggshell to prove it had died within an egg. Using modern imaging techniques, we were able to answer that question definitively,” she says. “It is also thrilling because this discovery breaks entirely new ground. For over 150 years of South African palaeontology, no fossil had ever been conclusively identified as a therapsid egg. This is the first time we can say, with confidence, that mammal ancestors like Lystrosaurus laid eggs, making it a true milestone in the field”.

Professor Benoit says this matters not just for what it tells us about the past but for the impact it brings to the modern context.

“This research is important because it provides the first direct evidence that mammal ancestors, such as Lystrosaurus, laid eggs, resolving a long-standing question about the origins of mammalian reproduction. Beyond this fundamental insight, it reveals how reproductive strategies can shape survival in extreme environments: by producing large, yolk-rich eggs and precocial young, Lystrosaurus was able to thrive in the harsh, unpredictable conditions following the end-Permian mass extinction. In a modern context, this work is highly impactful because it offers a deep-time perspective on resilience and adaptability in the face of rapid climate change and ecological crisis. Understanding how past organisms survived global upheaval helps scientists better predict how species today might respond to ongoing environmental stress, making this discovery not just a breakthrough in palaeontology, but also highly relevant to current biodiversity and climate challenges.” he explains.

Scientists believe that understanding how life survived Earth’s worst-ever extinction event can offer lessons for our own time in a period of rapid climate change, habitat loss, and species decline. Lystrosaurus teaches us that when the world falls apart, the survivors are often those who adapt their most fundamental biology.