Accurately determining the age of dinosaur fossils has historically been challenging for paleontologists. Now, a new study in Communications Earth & Environment shows that fossilized dinosaur eggshells contain a radioactive time signature that allows scientists to more precisely date these prehistoric nesting sites.
Many traditional methods for determining the age of fossils often depend on naturally occurring minerals that can record time through radioactive decay. These minerals are typically present in volcanic ash layers; however, many fossil sites lack the volcanic material required to utilize this technique.
Directly dating bones or teeth is also often unreliable. After burial, groundwater alters the radioactive signals in fossils, producing a wide range of estimated ages. Therefore, many infamous fossil sites still lack precise age estimates to this day.
Dinosaur eggshells consist mainly of the mineral calcite. After burial, groundwater can introduce small amounts of uranium into the calcite early in the fossilization process. Over millions of years, this uranium eventually turns into lead.
If the calcite remains stable, its uranium and lead content records the timing of burial. This allows fossilized eggshells to act as natural timekeepers. Before this study, scientists were unsure whether eggshell calcite could retain this signal for tens of millions of years.
Eggshells vs Bones
To test their idea, the team studied fossilized eggshells found in Utah and the Gobi Desert in Mongolia. They used uranium–lead dating and special mapping to measure tiny amounts of uranium and lead inside the calcite crystals. This method provided the first direct age for the samples from Mongolia, indicating that the eggs and nests are about 75 million years old.
The ages determined from uranium–lead dating of the eggshells closely matched results from other dating methods, sometimes within five percent of previous estimates. This shows that dinosaur eggshells can serve as a reliable alternative for radiometric dating. In certain situations, fossilized eggshells could provide more reliable results than fossilized bones and teeth.
“Eggshell calcite is remarkably versatile,” said lead author Dr. Ryan Tucker of Stellenbosch University. “It gives us a new way to date fossil sites where volcanic layers are missing, a challenge that has limited paleontology for decades.”
The calcite found in these fossilized eggshells is more resistant to subsequent chemical changes, at least in the cases studied here. If uranium enters the calcite early, the lead that forms preserves a steady time signal. This makes eggshells very useful in places where volcanic minerals are rare, but fossil eggs are readily available.
A New Tool for Dinosaur Research
Directly dating fossilized eggshells could help scientists create more accurate timelines for dinosaur evolution, nesting, and species changes. Researchers can now place previously hard-to-date sites more precisely in time, making it easier to compare fossils across locations.
“Direct dating of fossils is a paleontologist’s dream,” said study co-author Lindsay Zanno, associate research professor at North Carolina State University and head of paleontology at the North Carolina Museum of Natural Sciences. “Armed with this new technique, we can unravel mysteries about dinosaur evolution that used to be insurmountable.”
While this study could be a breakthrough, researchers say eggshell dating is not meant to replace other methods. Instead, it gives scientists a new option for sites where other established methods cannot be used. In paleontology, this means that some previously difficult-to-date fossil sites may now be placed on a firmer timeline using material left by the dinosaurs themselves.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds a Master of Business Administration, a Bachelor of Science in Business Administration, and a Data Analytics certification. His work combines analytical training with a focus on emerging science, aerospace, and astronomical research.