A new dating method directly ages fossil eggshells using uranium–lead dating and elemental mapping of trace uranium and lead in calcite, treating eggshells as natural geochronometers.

The approach offers broad global applicability for dating fossil sites without volcanic layers, potentially unlocking precise timelines for dinosaur evolution and paleoecology.

Eggshell calcite dating provides an age determination pathway at sites lacking volcanic ash, expanding the toolkit for deep-time reconstruction.

The study, published in Communications Earth & Environment, includes coauthor Lindsay Zanno and is funded by the National Geographic Society.

Researchers acknowledge the method is early-stage but shows promise for improving age assessments at ecosystems and evolutionary questions where ash layers are absent.

Lead researcher emphasizes that using multiple dating tools strengthens our ability to reconstruct accurate timelines for ancient life.

Future work will refine how eggshells incorporate radioactive elements and establish reliability checks, with ongoing support from the National Geographic Society.

The method could benefit other egg-rich sites without volcanic ash, such as South Africa’s Elliot Formation and Patagonia’s Auca Mahuevo, enhancing understanding of dinosaur evolution and ecosystems.

Eggshell dating can be as reliable as, or more reliable than, traditional methods when ash layers are missing.

Co-author notes that direct fossil dating via eggshells marks a major advance for understanding deep-time biology and Earth history.

Co-authors highlight the significance of directly dating fossils for unraveling questions about dinosaur evolution and deep-time biogeography.

Tests in Utah and Mongolia showed dating accuracy within about 5% of precise volcanic-ash dates, with Mongolia yielding the first direct age for a locality preserving dinosaur eggs and nests around 75 million years ago.

In Mongolia, the team dated Teel Ulaan Chaltsai eggs to roughly 75 million years ago, placing those dinosaurs in the Late Cretaceous.

The Mongolia locality represents the first direct age for a site preserving dinosaur eggs and nests, dating to approximately 75 million years ago.

The accompanying article is titled “U–Pb calcite age dating of fossil eggshell as an accurate deep time geochronometer” and was published in Communications Earth & Environment on November 10, 2025.

This technique complements bone and tooth dating and can overcome limitations when zircon or apatite are absent at fossil sites.

Overall, the method adds a flexible dating tool for sites lacking volcanic layers, with potential to transform cross-time and cross-region paleontological correlations.

The study, led by Dr. Ryan Tucker, used uranium–lead dating and elemental mapping to measure uranium and lead in eggshell calcite as a geological clock.

International collaboration involving the United States, Mongolia, Brazil, and South Africa, with fieldwork supported by MADEx, the National Geographic Society, and the National Science Foundation.

In Utah, oviraptorosaur eggs between ash layers dated to about 99 million years yielded U–Pb dates around 97 million years, aligning closely with ash-derived ages.