Dinosaur eggshells unlock a new way to tell time in the fossil record
November 10, 2025
An international team of geologists and paleontologists is pioneering a groundbreaking methodology to reliably determine the age of fossil-bearing rocks — by directly dating fossilized dinosaur eggshells.
The study — co-authored by Ryan Tucker from Stellenbosch University, Lindsay Zanno from the North Carolina Museum of Natural Sciences and North Carolina State University, and colleagues — was published in Communications Earth & Environment.
Many fossil sites around the world are only coarsely dated. Without precise information on the geologic age of fossils, paleontologists struggle to understand how different species and ecosystems relate across time and space. Usually, researchers rely on dating minerals such as zircon or apatite found associated with fossils, but those minerals aren’t always present. Attempts to date the fossils themselves, such as bones or teeth, have often produced uncertain results.
Tucker’s team took a different approach. They used advanced uranium-lead (U-Pb) dating and elemental mapping to measure trace amounts of uranium and lead housed inside the calcite of fossilized dinosaur eggshells. These isotopes function like a natural clock, enabling scientists to determine when the eggs were buried.
Tests on dinosaur eggs from Utah (USA) and the Gobi Desert (Mongolia) showed that the eggshells record ages with an accuracy of about five percent relative to precise volcanic-ash dates. In Mongolia, the team determined the first-ever direct age — around 75 million years old — for a historic locality preserving dinosaur eggs and nests.
“Eggshell calcite is remarkably versatile,” says Tucker. “It gives us a new way to date fossil sites where volcanic layers are missing, a challenge that has limited paleontology for decades.”
By showing that dinosaur eggshells can reliably record the passage of geologic time, the study links biology and Earth science in a new way — offering researchers a powerful tool to date fossil sites around the globe.
“Direct dating of fossils is a paleontologist’s dream,” says Zanno. “Armed with this new technique, we can unravel mysteries about dinosaur evolution that used to be insurmountable.”
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