Frozen in time: 86-million-year-old Dinosaur eggs discovered in China
A clutch of 28 dinosaur eggs found in the Qinglongshan fossil reserve in central China is about 86 million years old, according to scientists who used an “atomic clock” method to date the samples. Researchers said they now hope the eggs and the technique employed to evaluate their age might help to reveal how dinosaurs living in China’s Yunyang Basin adapted to a cooling climate.
The dating technique used on the eggs, known more formally as carbonate uranium-lead, or U-Pb, dating, is a common process for determining the age of carbonate minerals that contain calcium, iron, manganese and magnesium. Uranium is present within these minerals, and over time, it decays into lead.
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Scientists used a micro-laser to shave off bits of fossilised eggshell samples, vaporised the mineral fragments and then counted the number of uranium and lead atoms. By evaluating the ratio of uranium to lead, they were able to of determine the age of the eggs.
Recent identification of calcite, a form of calcium carbonate in the fossil eggshells suggested that the eggs would be good candidates for U-Pb dating, researchers reported Thursday in the journal Frontiers in Earth Science.
The eggs are the first fossils to be reliably dated from the Qinglongshan fossil reserve, which includes three sites containing more than 3,000 eggs, the majority of which are semi-exposed and preserved in 3D, with their original shapes largely intact.
Most of the eggs there belong to the species Placoolithus tumiaolingensis in the Dendroolithidae family, a classification that is derived from the eggs rather than from a dinosaur’s fossil skeleton. (The dinosaur that laid the eggs has not yet been identified.) The eggs are slightly flattened spheres measuring about 4.7 to 6.7 inches (120 to 170 millimetres) long, with mineralised shells that are no more than 0.09 inch (2.4 millimetres) thick.
Eggshells in this group tend to be relatively porous for dinosaur eggs, and that feature could offer clues about this ancient ecosystem during the Cretaceous period (145 million to 66 million years ago), when Earth was already starting to cool down.
