The egg found and studied by scientists. The first of a mammalian ancestor
The egg of a Lystrosaurus offspring is the first from a mammalian ancestor to be discovered, providing the first direct evidence that mammalian ancestors laid eggs, one of the authors of a new investigation announced.
Which chicken which what. First the egg and then (thanks to it) us.
All mammals give birth to live young, with the exception of a small group of oviparous monotremes, such as the platypus. But will the ancestors of mammals also reproduced through eggs? This is a question that has intrigued evolutionary biologists for decades.
Researchers now finally have a definitive answeraccording to the results of a published on Thursday in PLOS Onebased on a 250 million year old fossilized egg, sophisticated technological advances — and a lot of patience.
Paleontologists discovered the specimen in question almost 17 years agoduring an excavation in the Karoo Basin in South Africa. This arid region, located more than 200 miles northeast of Cape Town, is particularly known for the enormous abundance of ancient fossils.
“My trainer and exceptional fossil discoverer, John Nyaphuliidentified a small nodule that, at first, revealed only tiny fragments of bone”, explained the paleobiologist Jennifer Bothafrom the University of the Witwatersrand, cited by .
As he carefully prepared the specimen, it became clear that it was a newly hatched chick of Lystrosaurusperfectly coiled.”
O Lystrosaurus it was a decisive species in the evolutionary trajectory of mammals. These herbivores appeared on the planet in the wake of the end of the Permian, around 252 million years ago.
Probably triggered by volcanic eruptions in present-day Siberia, this cataclysm ended eliminate about 57% of all biological lifeincluding 70% two terrestrial vertebrates. O Lystrosaurus managed to prosper despite the volatile climate of the time, high temperatures and frequent droughts.
Reconstruction of a Lystrosaurus embryo inside its partially preserved shell
Although Botha and his colleagues suspected that the discovery showed the remains of a baby inside the shellthe imaging technology needed to test this hypothesis did not exist in 2008.
A few years later, however, the development of advanced synchrotron X-ray computed tomography opened the way for research. Botha took the fossil to the European Synchrotron Radiation Facility in France, where collaborators were finally able to examine it under the right conditions.
Only then did the researchers manage to identify a key piece of evidence: one incomplete mandibular symphysis. This section of the lower jaw is crucial for an animal to feed, but only after its two halves fuse during gestation.
“I was genuinely excited.“, recalled Julien Benoit, paleobiologist at the University of the Witwatersrand. “The fact that this merger has not yet occurred shows that this individual would be unable to feed itself”.
This means that the Lystrosaurus found by the team of researchers was not fully developed when he died, and that his position can only mean one thing: it was still inside an egg. More specifically, the team believes that the Lystrosaurus lay soft shell eggswhich explains why fossilized evidence is so difficult to find.
Although small, the egg is large compared to the body size of this mammalian ancestor. Today, larger eggs generally contain more yolk, which brings together all the nutrients an embryo needs to develop without being fed by its parents.
Bigger eggs too resist desiccation much bettera vital advantage in the harsh climate that followed the extinction event. Taken together, everything indicates that the Lystrosaurus It already had advanced development when it hatched. That allowed him to escape predators, take care of himself and quickly begin to reproduce.
In addition to filling an important gap in mammal evolution, Lystrosaurus could help biologists understand how species can continue to adapt to an increasingly chaotic ecosystem.
“This work has a big impact because it offers a long-term perspective on the resilience and adaptability in the face of rapid climate change and ecological crises,” said Benoit.
“This discovery [é] not only an advance in paleontology, but also highly relevant to current biodiversity and climate challenges”, he concludes.
