The ultra-bright light of the European Synchrotron in France (ESRF) has been shone on dinosaur eggs, enabling scientists to create the first 3D reconstructions of dinosaur embryos. Synchronton X-rays are so high-powered that they can scan extremely dense material, including fossils.
An international team of scientists led by the University of the Witwatersrand in South Africa enlisted the aid of the ESRF in Grenoble to get a closer look at a clutch of seven fossilized eggs, two with visibly exposed embryos, discovered in South Africa’s Golden Gate Highlands National Park in in 1976. They were identified as Massospondylus carinatus, a sauropodomorph dinosaur from the Jurassic period that could grow to be as much as 17 feet long. The herbivore roamed what is now South Africa 200 million years ago.
Because the embryonic dinosaur bones are so tiny, very little information could be drawn from visual examination. They appeared to be fully developed skeletally. The ESRF scans revealed that in fact the embryos were only 60% developed. The team compared the tiny bones in their skulls with those from living descendants of the dinosaurs (crocodiles, chickens, turtles, lizards) which ossify in a similar way: starting at the tip of the snout and concluding with the top and back of the skull. The cranial ossification sequence indicated the dinosaur embryos were not close to hatching and that they had another 40% of their time in ovo left to serve.
The team 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 those of adults, and would be the ones that the embryos hatched with. “I was really surprised to find that these embryos not only had teeth, but had two types of teeth. The teeth are so tiny; they range from 0.4 to 0.7 mm wide. That’s smaller than the tip of a toothpick,” says [University of Witwatersrand researcher] Kimi Chapelle.
The researchers concluded that the 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,” says Jonah Choiniere, professor at the University of Witwatersrand and also co-author of the study.
The study has been published in the journal Scientific Reports and can be read online.