Paris (AFP)

A long hunt for eggs: scientists have managed, thanks to X-rays, to unravel the mystery of the interior of dinosaur eggs 200 million years old, which revealed tiny embryonic skulls, with similar development to those of modern reptiles, according to a study published Thursday.

These embryos of "Massospondylus carinatus", a 5 meter long herbivore, which are among the oldest in the world, had been discovered in 1976 in the Golden Gate Highlands National Park in South Africa, and because of their fragility and of their very small size, they remained difficult to study for a long time, for lack of a non-destructive scientific method.

But in 2015, an international scientific team brought seven eggs (only three of which contained embryos) to the European synchrotron in Grenoble (ESRF) in France, to scan them, explains the study published in the journal Scientific Reports.

The powerful X-rays produced by the ESRF, via electrons accelerated at the speed of light in a ring more than 800 meters long, revealed an unprecedented level of detail, showing up to the bone cells.

These data notably made it possible to reconstruct a 3D model of the baby dinosaur skull, only about two centimeters long. Scientists compared their results to embryos of the closest modern relatives of dinosaurs (crocodiles, turtles, lizards ...), and found similarities in the stages of development, especially in the way the skull grows in the egg.

"What surprised me most was how much younger the embryos were than we thought," Kimberley Chapelle, the study's lead author, told AFP. were only 60% of their embryonic development.

They also had two types of preserved teeth in their jaws, the first of which "fell before hatching, just like geckos and crocodiles today". "They're smaller than the tip of a toothpick!" Added the researcher from the University of the Witwatersrand in Johannesburg.

The study concludes that these dinosaurs "developed in their eggs in a similar way to their reptilian parents, whose embryonic development pattern has not changed in 200 million years", according to a press release accompanying the publication of the study.

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