Mammal ancestors laid eggs--and this 250-million-year-old fossil proves it

[erronis]

https://phys.org/news/2026-04-mammal-ancestors-laid-eggs-million.html
Wits University

Egg photographed in the control room of the ESRF in France. Credit: Professor Julien Benoit

A remarkable new discovery is shedding light on one of the greatest survival stories in Earth's history, and answering a decades-old scientific mystery. Lystrosaurus, a hardy, plant-eating mammal ancestor, rose to prominence in the wake of the End-Permian Mass Extinction some 252 million years ago, the most devastating extinction event our planet has ever experienced.

While countless species vanished, Lystrosaurus not only survived but thrived in a world marked by extreme environmental instability, intense heat, and prolonged droughts.

Now, groundbreaking research published in PLOS ONE reveals a discovery that transforms our understanding of this iconic survivor. An international team led by Professor Julien Benoit, Professor Jennifer Botha (Evolutionary Studies Institute, University of the Witwatersrand, South Africa), and Dr. Vincent Fernandez (ESRF--The European Synchrotron, France) has identified, for the first time, an egg containing an embryo of Lystrosaurus, dating back approximately 250 million years.

This extraordinary fossil represents the first-ever egg discovered from a mammal ancestor, finally answering a long-standing question: Did the ancestors of mammals lay eggs?

The answer is yes.

. . .