Artist’s reconstruction of a newly hatched troodontid-like dinosaur resting in fragments of its eggshell (based on a Mongolian microtroodontid type). These eggshells, when buried within ancient soil, interact with meteoric waters, causing the initial uranium to be incorporated into the eggshell calcite crystals. Credit: Eva Utsukiyouhei (宇津城遥平)
An international team of geologists and paleontologists is proposing a groundbreaking method for reliably determining the age of fossil-bearing rocks.
The study, led by Dr Ryan Tucker of the University of Stellenbosch’s Department of Earth Sciences, has been published. Communication Earth and Environment.
Many fossil sites around the world are only rough. Without precise information about the geologic ages of fossils, paleontologists struggle to understand how different species and ecosystems are related in time and space. Typically, researchers rely on dating minerals such as zircon or apatite associated with fossils, but those minerals are not always present. Attempts to date fossils themselves, such as bones or teeth, have often yielded inconclusive results.
Dr. Tucker’s team took a different approach. They used advanced uranium-lead (U-PB) dating and elemental mapping to measure the amount of uranium and lead residing within the calcite of fossilized dinosaur eggs. These isotopes act like a natural clock, helping scientists determine when the eggs were buried.
Tests on dinosaur eggs from Utah (US) and the Gobi Desert (Mongolia) have shown that the eggshells record ages with an accuracy of about 55% compared to the exact dates of the volcanoes and fossils. In Mongolia, the team made a direct age determination for the first time—about 75 million years old—for a prehistoric site that preserved 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 colleagues from the North Carolina Museum of Natural Sciences, North Carolina State University, Colorado School of Mines, Institute of Paleontology of the Mongolian Academy of Sciences, Universidad Federal de Oro Preto (Brazil). Fieldwork in Mongolia was conducted by the Mongolian Alliance for Dinosaur Exploration (MAMES) and was 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.
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Looking at the exposed fossiliferous strata of Tell Alan Chaltsai, a fossil locality in the Senshend Sub-Basin, Eastern Gobi Basin, Mongolia. The team dated the eggshell from the area of Tell Alan Chaltsai. Credit: Ryan Tucker
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Comparative elemental mapping of the isotopes uranium (U) and lead (Pb) used for age dating of fossilized eggshells collected from the Mustochet Member, Cedar Mountain Formation, Utah (US). The maps show that in the American sample, uranium (U) entered the eggshell after fossilization, while the Tell Alan Chaltsai samples show uranium (U) before fossilization. Credit: Kira Venter and Chris Luna
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A preliminary map of strontium (Sr) isotopes from dinosaur eggshells collected from Tell Ilan Chaltsai, Eastern Gobi Basin. The elemental maps were used by the researchers to assess if the uptake of strontium (Sr) was evenly distributed in the eggshell. The uniform distribution indicates that this and other isotopes occurred after burial but before fossilization. Credit: Kira Venter and Chris Luna
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This team from Stellenbosch University (SU) developed a new method to age-date fossilized dinosaur eggs, using the Pneuma Multicollector, Induced Coupled Plasma, Mass Spectrometer (MC-ICP-MS) instrument, which is hosted in the Elemental and Isotope Analysis Laboratory in SU’s Department of Earth Sciences. They are, from left to right, Professor Chris Luna, MSc student Kira Venter, and Dr Ryan Tucker. With the ability to measure multiple isotopes simultaneously with high precision and accuracy, MC-ICP-MS is uniquely suited to address a wide range of research questions. Credit: Stephen Ellis
“Direct dating of fossils is a paleontologist’s dream,” says study co-author Lindsey Zano, associate research professor at North Carolina State University and chief of paleontology at the North Carolina Museum of Natural Sciences. “Armed with this new technique, we can uncover mysteries about dinosaur evolution that used to be intractable.”
More information:
Ryan T. Tucker et al., UPB calcite age dating of fossil eggshells as an accurate deep-time geochronometer, Communication Earth and Environment (2025) doi: 10.1038/S43247-025-02895-W.
Provided by Stellenbosch University
Reference: Unlocking a new way to tell time in the fossil record (2025, November 10) Retrieved November 10, 2025 from https://phys.org/news/2025-11-dinosaur-eggshells-fossill.html.
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