Artistic reconstruction of a newly hatched troodontid-like dinosaur resting among fragments of its eggshell (loosely based on Mongolian microtroodontid-type). These eggshells, when buried within ancient soil, interacted with meteoric waters, leading to early uranium incorporation into the eggshell calcite crystals. Credit: Eva Utsukiyouhei (宇津城遥平)

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, led by Dr. Ryan Tucker from Stellenbosch University’s Department of Earth Sciences, is 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.

Dr. 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.

This team from Stellenbosch University (SU) developed a novel method to age-date fossilized dinosaur eggs, using a Neoma Multi-Collector, Inductively Coupled Plasma, Mass Spectrometer (MC-ICP-MS) instrument, hosted in the Elemental and Isotope Analysis Laboratory in SU’s Department of Earth Sciences. With its capacity to measure multiple isotopes simultaneously at very high precision and accuracy, the MC-ICP-MS is uniquely suited to addressing a wide range of research questions—from tracing fluid–rock interactions and quantifying elemental cycling in natural systems, to reconstructing ancient ocean chemistry and refining high-resolution geochronological frameworks. Credit: Stefan Els, Stellenbosch University

Tests on dinosaur eggs from Utah (U.S.) and the Gobi Desert (Mongolia) showed that the eggshells record ages with an accuracy of about 5% 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 Dr. Tucker. “It gives us a new way to date fossil sites where volcanic layers are missing, a challenge that has limited paleontology for decades.”

The work involved collaborators from the North Carolina Museum of Natural Sciences, North Carolina State University, Colorado School of Mines, Mongolian Academy of Sciences’ Institute of Paleontology, Universidade Federal de Ouro Preto (Brazil). Fieldwork in Mongolia was carried out through the Mongolian Alliance for Dinosaur Exploration (MADEx) and supported by the National Geographic Society and the National Science Foundation.

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.

• Looking out across the exposed fossil-bearing strata of the fossil locality Teel Ulaan Chaltsai, located in the Sainshand Sub-basin, Eastern Gobi Basin, Mongolia. The team dated eggshell from the Teel Ulaan Chaltsai locality. Credit: Ryan Tucker
• Comparative elemental map of isotopes uranium (U) and lead (Pb) that were used for age dating fossil eggshell collected from the Mussentuchit Member, Cedar Mountain Formation, Utah (U.S.). Maps indicate that in the U.S. sample, Uranium (U) penetrated the eggshell after fossilization, whereas the samples from Teel Ulaan Chaltsai show uranium (U) before fossilization. Credit: Kira Venter & Chris Luna
• Elemental map of the isotope strontium (Sr) from dinosaur eggshell collected from Teel Ulaan Chaltsai, Eastern Gobi Basin. Elemental maps were used by the researchers to evaluate if the uptake of strontium (Sr) was uniformly distributed across the eggshell. A uniform distribution indicates that uptake of this and other isotopes occurred after burial but prior to fossilization. Credit: Kira Venter & Chris Luna
• This team from Stellenbosch University (SU) developed a novel method to age-date fossilized dinosaur eggs, using a Neoma Multi-Collector, Inductively Coupled Plasma, Mass Spectrometer (MC-ICP-MS) instrument, hosted in the Elemental and Isotope Analysis Laboratory in SU’s Department of Earth Sciences. They are, from left to right, Prof Chris Luna, MSc student Kira Venter, and Dr. Ryan Tucker. With its capacity to measure multiple isotopes simultaneously at very high precision and accuracy, the MC-ICP-MS is uniquely suited to addressing a wide range of research questions—from tracing fluid–rock interactions and quantifying elemental cycling in natural systems, to reconstructing ancient ocean chemistry and refining high-resolution geochronological frameworks. Credit: Stefan Els

“Direct dating of fossils is a paleontologist’s dream,” says 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.”

More information: Ryan T. Tucker et al, U-Pb calcite age dating of fossil eggshell as an accurate deep time geochronometer, Communications Earth & Environment (2025). DOI: 10.1038/s43247-025-02895-w

Citation: Dinosaur eggshells unlock a new way to tell time in the fossil record (2025, November 10) retrieved 10 November 2025 from https://phys.org/news/2025-11-dinosaur-eggshells-fossil.html

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