Scientists Use X-rays to Peer inside Fossilized Dinosaur Eggs

Saturday, April 11, 2020

The clutch of Massospondylus carinatus eggs. Image credit: Brett Eloff.

Powerful X-ray beams at the European Synchrotron in France allowed an international team of researchers to study some of the world’s oldest and well-preserved dinosaur embryos and reconstruct them in 3D.

The clutch of seven subspherical dinosaur eggs was recovered from the Elliot Formation of Golden Gate Highlands National Park in South Africa in 1976. Two partially exposed embryos in the clutch were quickly identified as being dinosaurian, making them among the oldest known dinosaur eggs and embryos in the world.

The fossilized eggs belong to Massospondylus carinatus, a 5-m-long sauropodomorph dinosaur that lived approximately 200 million years ago (Jurassic period).

“At the ESRF, an 844-m-long ring of electrons traveling at the speed of light emits high-powered X-ray beams that can be used to non-destructively scan matter, including fossils,” the paleontologists explained.

“The embryos were scanned at an unprecedented level of detail — at the resolution of an individual bone cell.”

With these data in hand, they were able to create a 3D model of Massospondylus carinatus’ embryonic skull.

Watercolor painting of the Massospondylus carinatus embryos at 17% through the incubation period, 60% through the incubation period and 100% through the incubation period. Image credit: Mélanie Saratori.

“No lab CT scanner in the world can generate these kinds of data. Only with a huge facility like the ESRF can we unlock the hidden potential of our most exciting fossils,” said Dr. Vincent Fernandez, a scientist at the Natural History Museum in London, UK.

The researchers noticed similarities between the dinosaur embryos and the developing embryos of crocodiles, chickens, turtles, and lizards.

“By comparing which bones of the dinosaur embryonic skull were present at different stages of their development, we can now show that the Massospondylus carinatus embryos were actually much younger than previously thought and were only at 60% through their incubation period,” they said.

“We also found that each embryo had two types of teeth preserved in its developing jaws.”

“One set was made up of very simple triangular teeth that would have been resorbed or shed before hatching, just like geckos and crocodiles today. The second set was very similar to that of adults, and would be the ones that the embryos hatched with.”

Digital reconstructions of Massospondylus carinatus embryonic skulls. Image credit: Chapelle et al, doi: 10.1038/s41598-020-60292-z.

“I was really surprised to find that these embryos not only had teeth, but had two types of teeth,” said Dr. Kimi Chapelle, a researcher at the University of Witwatersrand.

“The teeth are so tiny; they range from 0.4 to 0.7 mm wide. That’s smaller than the tip of a toothpick.”

The team concluded that dinosaurs developed in the egg just like their reptilian relatives, whose embryonic developmental pattern hasn’t changed in 200 million years.

“It’s incredible that in more than 250 million years of reptile evolution, the way the skull develops in the egg remains more or less the same. Goes to show — you don’t mess with a good thing,” said Professor Jonah Choiniere, also from the University of Witwatersrand.

The study was published in the journal Scientific Reports.


K.E.J. Chapelle et al. 2020. Conserved in-ovo cranial ossification sequences of extant saurians allow estimation of embryonic dinosaur developmental stages. Sci Rep 10, 4224; doi: 10.1038/s41598-020-60292-z