In a paleontology “first”, a new method has been developed to directly date dinosaur eggs by using lasers to analyze eggshell fragments.
The researchers from the Hubei Institute of Geosciences in China detailed this new method in a study published on September 11.
Interestingly, the laser-based method led to successfully dating a cluster of dinosaur eggs from the Qinglongshan site, central China, to 85 million years ago (Late Cretaceous period).
The fossilised eggs, belonging to the species Placoolithus tumiaolingensis, are the first from this site to be reliably dated.
“We provide the first robust chronological constraints for these fossils, resolving long-standing uncertainties about their age,” said Dr Bi Zhao, corresponding author and a researcher at the institute, in a press release.
Reliable dating method
Dating dinosaur eggs has typically been a challenge due to dependency on indirect methods, such as dating surrounding volcanic rocks.
This approach is unreliable because the proxy materials, like volcanic rock, might have been changed by geological processes or created long after the eggs were laid, resulting in incorrect age estimates.
Notably, the new technique called carbonate uranium-lead (U-Pb) dating offers a more direct and reliable solution.
It works by firing a micro-laser at an eggshell fragment to measure the ratio of uranium to lead atoms within the carbonate minerals of the shell itself.
“We fired a micro-laser at eggshell samples, vaporizing carbonate minerals into aerosol. This is analyzed by a mass spectrometer to count uranium and lead atoms. Since uranium decays into lead at a fixed rate, we were able to calculate the age by measuring accumulated lead— it’s like an atomic clock for fossils,” Zhao explained.
The team tested this technique on dinosaur eggs found at the Qinglongshan site in the Yunyang Basin.
The site is said to be China’s first national dinosaur egg fossil reserve, holding as many as 3,000 fossilized eggs across three locations.
The majority of these fossils are believed to belong to the species Placoolithus tumiaolingensis, a type of dinosaur known for having highly porous eggshells.
The specific egg sample used for dating came from a cluster of 28 eggs found within breccia-bearing siltstone.
Cretaceous period climate change
The new dating method revealed that the dinosaur eggs are approximately 85 million years old, with a margin of error of 1.7 million years.
“It revolutionizes our ability to establish global dinosaur egg chronologies,” Zhao said.
The Cretaceous period was a time of major global change, marked by intense volcanic activity and mass extinctions.
Fossils from this era provide scientists with valuable clues about the past climate.
The dinosaur eggs were laid during the Turonian epoch of the Late Cretaceous, millions of years after a period of global cooling had already begun.
This shift to a cooler climate likely contributed to a decline in dinosaur diversity and may have affected the egg-laying habits of species at the Qinglongshan site.
“Dendroolithids’ [species group] specialized pore structures may represent evolutionary adaptations to this climatic shift, as novel egg types emerged worldwide during cooling,” Zhao said.
“P. tumiaolingensis may represent an evolutionary dead end where the egg-laying dinosaur population failed to adapt successfully to cooling climates,” Zhao explained.
Researchers are already planning to expand their sampling, looking at eggs from different rock layers to build an even more detailed regional timeline.
The team highlights that this dating method is important for understanding dinosaur evolution, extinction events, and environmental changes during the Late Cretaceous period.
The findings were reported in the journal Frontiers in Earth Science.