The world's oldest eggs originate from the predecessors of the huge long-necked sauropods. Known as prosauropods, they already reached a size of four to twelve metres. Taiwanese palaeontology professor Timothy D. Huang discovered the eggs in Yunnan in southwest China in 2013. Some years earlier, researchers such as the Canadian palaeontologist Professor Robert Reisz had already come across similar examples in South Africa and in Argentine Patagonia. The eggs found more recently have now been studied at Reisz's university in Toronto. The researchers were not surprised by the locations in which the eggs were discovered. "Prosauropods were spread all over the world", explains Martin Sander from the University of Bonn. A professor of palaeontology, he was a member of the team that studied the eggs. "Of greater interest is the fact that the finds of the oldest eggs date back to the same period in all continents – and that no older ones exist. After all, we know that the predecessors of reptiles and mammals were already laying eggs 315 million years ago." This leads the researchers to conclude that earlier eggshells were made of a leathery material, as snake and lizard eggs are today – and that they were unable to fossilise because they contained no minerals.
Charting the evolutionary process
For Sander and his colleagues, one important question to be answered is how eggs came to develop the ability to store minerals. Eggs with hard shells are likely to have proven advantageous from an evolutionary point of view because this gave them greater stability and protection. They also allowed larger animals to hatch from them, explains Sander. This is interesting because researchers have been working for decades to understand the "gigantism of sauropods" – that is to say, why dinosaurs became so huge.
As far as the question of mineralisation is concerned, the researchers currently presume that a role was played by a change in the oxygen content of the air. "210 million years ago, it was only 12 to 15 percent. It rose sharply during the period to which the fossilised eggs date back. We assume that the mineralisation process required oxygen", explains the Bonn palaeontologist, adding that this has not yet been conclusively proven in tests involving for example modern-day chicken eggs.
These findings came about as a side-line of research conducted by the research group "Biology of the Sauropod Dinosaurs: The Evolution of Gigantism", says Sander. The group is funded by the Deutsche Forschungsgemeinschaft (DFG). Since 2004, the researchers have been exploring questions such as how the largest land animals of all time ended up so big. The palaeontologist Martin Sander is the spokesperson for the interdisciplinary team, which is made up of scientists in the fields of palaeontology, zoology, animal nutrition, geochemistry and engineering science. Sander promises that he will one day write a book on the subject for a general readership. But first, in September, he will be opening an exhibition at Museum Koenig in Bonn, a previous version of which he had already curated at the American Museum of Natural History in New York. Its title, of course, was: "The World's Largest Dinosaurs".
Institut für Geowissenschaften und Meteorologie der Universität Bonn (only in German)
The institute was founded in 2018 as the result of a merger of the Geological Institute, the Institute of Mineralogy and Petrology, the Institute of Palaeontology and the Meteorological Institute. Its goal is to intensify cooperation between the researchers and teachers in the participating disciplines. The Goldfuß Museum, one of the most important palaeontological museums at German universities, belongs to the institute. It exhibits fossils from all over the world, together with marine reptiles and a tyrannosaurus skull.www.steinmann.uni-bonn.de (only in German)