Researchers studying a 250-million-year-old fossil have found the first proof that the ancestors of mammals laid eggs, and the discovery also sheds light on a remarkable story of survival.
The fossil, found in South Africa, belongs to a rolled-up embryo of a Lystrosaurus, an ancestor of mammals famous for surviving a occurred 252 million years ago, known as the “Great Extinction”, according to a study published in .
A team of researchers examined the fossil using high-resolution computed tomography and a synchrotron, which produces X-rays brighter than the sun, and discovered that the Lystrosaurus embryo’s jaws were not completely fused.
This feature, found only in embryos of modern birds and turtles, proves that the Lystrosaurus embryo was inside an egg when it died, he told CNN the study’s lead author, Julien Benoit, associate professor at the Institute of Evolutionary Studies at the University of the Witwatersrand in South Africa.
“This is the first time we can say with confidence that ancestors of mammals like Lystrosaurus laid eggs, which represents a true milestone in the field,” said Benoit.
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Benoit claimed that these eggs would have a soft, leathery outer shell, as hard-shelled eggs did not evolve until at least 50 million years later.
The fossil also offers a possible explanation for the long-standing mystery of why Lystrosaurus survived the “Great Extinction” – the which ended the Permian geological period, in which 90% of all living things on Earth died as the planet became much hotter and drier, he added.
“Lystrosaurus lived in a very dry, desert-like environment,” Benoit said, adding that it likely foraged for food in dry riverbeds and looked for soft, muddy soils to dig burrows and survive long periods of drought.
