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Dinosaur egg fossil sampled for geochronology.
Credit: Dr Bi Zhao
The dating of a clutch of fossil dinosaur eggs will leave creationists scrambling for excuses to dismiss the evidence and cling to the childish notion that Earth is only 6,000–10,000 years old, created ex nihilo by magic, with all extant and extinct species brought into existence without ancestors just a few days later. In other words, this discovery is yet another small addition to the mountain of evidence showing that the biblical creation story was the work of ignorant Bronze Age people trying to make sense of the world around them, not the word of an omniscient creator god who would have known better.
An added problem for creationists is that the research team used a new method of dating the eggs based on measuring when the eggshell itself formed, rather than relying solely on dating the rock in which the eggs were embedded. The difficulty with the latter approach is that, while it gives the age of the surrounding rock, the mineral grains in that rock may predate the eggs and could have been transported there by water or wind.
The new technique is conceptually similar to the uranium–lead (U–Pb) method used to date zircon crystals in volcanic tuff. Tiny amounts of uranium, which readily substitute into the crystal lattice, are incorporated when the zircon forms, but lead is excluded. Over time, uranium isotopes decay into stable isotopes of lead. Thus, any lead present within a zircon crystal must have come from radioactive decay, and by measuring the ratio of uranium to lead isotopes, scientists can calculate the crystal’s age with high precision.
A very similar process occurs in the carbonate of dinosaur eggshells: uranium is incorporated during formation, but lead is excluded. Measuring uranium–lead isotope ratios in the shell carbonate therefore provides a direct and highly accurate age for the eggs themselves, leaving little room for error.
Background^ U–Pb Dating of Carbonates. Uranium–lead (U–Pb) dating is one of the most reliable radiometric methods. It works because uranium isotopes (\(^{238}\text{U}\) and \(^{235}\text{U}\)) are unstable and decay into stable lead isotopes (\(^{206}\text{Pb}\) and (\(^{207}\text{Pb}\)) at known rates. The half-lives are very long — about 4.47 billion years for \(^{238}\text{U}\) and 704 million years for \(^{235}\text{U}\) — which makes the method well suited to dating ancient materials.The discovery is the subject of an open-access paper in the journal Frontiers in Earth Science and is described in a science news release from Frontiers.
When carbonate structures (such as eggshells, corals, or cave formations) form, small amounts of uranium are incorporated, but lead is excluded. Any lead later found in the structure must have formed by radioactive decay of uranium already present.
The age \(t\) of a sample is calculated from the ratio of parent to daughter isotopes using the basic decay equation: \[t = \frac{1}{\lambda} \ln\!\left(1 + \frac{D}{P}\right) \notag\] where:
- \(t\) = age of the sample
- \(\lambda\) = decay constant of the uranium isotope
- \(D\) = number of daughter atoms (lead isotopes)
- \(P\) = number of remaining parent atoms (uranium isotopes)
Because uranium has two naturally occurring isotopes that decay to different lead isotopes, scientists can cross-check ages using both \(^{238}\text{U}\) → \(^{206}\text{Pb}\) and \(^{235}\text{U}\) → \(^{207}\text{Pb}\) decay chains. Agreement between the two provides a strong internal consistency test and increases confidence in the results. Applied to dinosaur eggshell carbonate, this method gives a direct and highly accurate age for when the shell formed — rather than relying on the potentially older or younger sediments surrounding it.
Newly dated 85-million-year-old dino eggs could improve understanding of Cretaceous climate
Dating dinosaur eggs is difficult: available methods are limited and prone to errors because measurement proxies – such as volcanic rocks or crystals – may have changed between egg laying and dating attempts. Now, in a first for paleontology, researchers used a new method to date dinosaur eggs by firing lasers at eggshell fragments. This way, eggs in central China have been dated to the late Cretaceous, making them about 85 million years old. The findings could tell researchers about dinosaur populations and the climate millions of years ago.
In the Cretaceous period, Earth was plagued by widespread volcanic activity, oceanic oxygen depletion events, and mass extinctions. Fossils from that era remain and continue to give scientists clues as to what the climate may have looked like in different regions.
Now, researchers in China have examined some of them: dinosaur eggs found at the Qinglongshan site in the Yunyang Basin in central China. This is the first time that dinosaur eggs have been dated using carbonate uranium-lead (U-Pb) dating. The team published their results in Frontiers in Earth Science.
We show that these dinosaur eggs were deposited roughly 85 million years ago, in the Late Cretaceous period. We provide the first robust chronological constraints for these fossils, resolving long-standing uncertainties about their age.
Dr Bi Zhao, corresponding author
Hubei Institute of Geosciences
Hubei Geological Bureau, Wuhan, China.
New dates
Qinglongshan is China’s first national dinosaur egg fossil reserve. There, more than 3,000 fossilized eggs are spread across three sites. Most fossils are embedded in different stones, such as breccias, breccia and siltstone mixes, and fine sandstones. The eggs have mostly remained in their original location and show only minimal deformation. The majority is thought to belong to a single species, Placoolithus tumiaolingensis, which belongs to the family Dendroolithidae, a group characterized by highly porous eggshells. The sampled calcite-filled dinosaur egg fossil came from a cluster of 28 eggs embedded within breccia-bearing siltstone.
Interior of Qinglongshan Dinosaur Egg Fossil Museum.Credit: Dr. Bi Zhao
To date the egg, the team used U-Pb dating.
We fired a micro-laser at eggshell samples, vaporizing carbonate minerals into aerosol. This is analyzed by a mass spectrometer to count uranium and lead atoms. Since uranium decays into lead at a fixed rate, we were able to calculate the age by measuring accumulated lead— it’s like an atomic clock for fossils.
Dr Bi Zhao.
The results showed that the eggs from this cluster were deposited around 85 million years ago, with the possibility of them having been deposited around 1.7 million years earlier or later. Their age means they’ve been laid during the Late Cretaceous, an epoch lasting from approximately 100 to 66 million years ago. They are the first reliably dated fossils from the Qinglongshan site.
Traditionally, dating dinosaur eggs involves indirect methods, such as dating volcanic rock, ash layers, or minerals around eggs. These, however, may have formed before or after the laying of the eggs, or geological processes may have altered them. The method used here allows for precise dating of eggs without having to rely on anything but the eggs themselves. “It revolutionizes our ability to establish global dinosaur egg chronologies,” Zhao said.
Dinosaur egg fossil sampled for geochronology.Credit: Dr. Bi Zhao.
Old climates
Global cooling had started several million years before the laying of the eggs, in the Turonian epoch (lasting from approximately 93.9 to 89.8 million years ago). By the time they were laid, temperatures had declined significantly. The transition from a warm to a cooler climate was likely a factor in dinosaurs’ diminishing diversity and may have affected how many eggs were laid by how many species at Qinglongshan.
'Dendroolithids’ specialized pore structures may represent evolutionary adaptations to this climatic shift, as novel egg types emerged worldwide during cooling.
Dr Bi Zhao.
The pore structure of Dendroolithidae eggs, which are markedly different from many other dinosaur eggs, may be one such adaptation.P. tumiaolingensis may represent an evolutionary dead end where the egg-laying dinosaur population failed to adapt successfully to cooling climates.
Dr Bi Zhao.
Although few eggshell samples were examined in this study, all tests confirmed similar ages of egg fragments, which were also consistent with the age of the rocks surrounding the eggs. The team will be expanding sampling to include eggs found in different rock layers, which could help construct a regional timeline. They also said that Dendroolithid eggs in neighboring basins should be examined in the future to trace dinosaur migrations.
Our achievement holds significant implications for research on dinosaur evolution and extinction, as well as environmental changes on Earth during the Late Cretaceous. Such findings can transform fossils into compelling narratives about Earth’s history.
Dr Bi Zhao.
Dinosaur egg fossil sampled for geochronology.Credit: Dr Bi Zhao
Aerial view of Qinglongshan Dinosaur Egg Fossil Site.Credit: Dr Bi Zhao
Publication:
Abstract
The Cretaceous Period, marked by global events such as volcanic activity, oceanic anoxic episodes, and the end-Cretaceous mass extinction, has been extensively studied in marine records. However, terrestrial Cretaceous systems remain understudied except in regions like northeastern China. Dinosaur eggs, abundant in Upper Cretaceous terrestrial strata, provide critical insights into paleoenvironments, climate, and biotic evolution. The Qinglongshan site in Yunyang District, Shiyan, Hubei Province, preserves thousands of semi-exposed, three-dimensionally intact dinosaur eggs with minimal deformation, offering a rare opportunity to study nesting behavior and environmental dynamics. Preliminary studies classified these eggs as Placoolithus tumiaolingensis (Dendroolithidae), but their chronostratigraphic context remains poorly constrained, hindering regional correlations. This study addresses this research gap by applying Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometer (LA-MC-ICP-MS) U-Pb dating to biogenic calcite samples from egg - bearing horizons, and the test results indicate a depositional age (DA) of 85.91 ± 1.74 Ma. The results aim to establish a robust chronological framework for the Qinglongshan egg assemblage for the first time, enhancing understanding of Late Cretaceous terrestrial ecosystems in China’s interior and their response to global environmental changes. This study underscores the potential of dinosaur egg fossils as proxies for reconstructing the “Cretaceous World” in terrestrial settings.
1 Introduction
The Cretaceous period has garnered significant attention due to a series of major global events, including widespread volcanic activity, oceanic anoxic events, superchrons, biotic radiation, and mass extinctions (Jones and Jenkyns, 2001; Bralower et al., 1994; Cronin et al., 2001.1; Walliser, 1996; Leckie et al., 2002). However, most studies have focused on marine strata and fossil records from the Cretaceous. In contrast, research on terrestrial Cretaceous systems remains limited, except in regions such as northeastern China, where studies have achieved relatively higher resolution (Xi et al., 2019). In other areas, critical environmental-biological events in terrestrial Cretaceous settings are often difficult to define due to challenges in stratigraphic correlation or incomplete fossil records (Zhao et al., 2013).
Dinosaur eggs are a common fossil type in Upper Cretaceous terrestrial strata. They exhibit diverse microscopic shell structures and nesting patterns, and have been discovered in various sedimentary environments (Horner and Makela, 1979; Cousin et al., 1994.1; Mikhailov et al., 1994.2; Zhao, 2003; Sander et al., 2008). These fossils provide critical insights into regional stratigraphic correlation, paleoenvironmental reconstruction, and paleoclimate studies (Zhao et al., 2015). In recent years, research on dinosaur egg fossils, their burial chronologies, and associated environmental contexts has emerged as an important approach to understanding the terrestrial “Cretaceous World” (He et al., 2013.1; Zhao et al., 2017; Han et al., 2022).
Abundant Late Cretaceous dinosaur egg fossils were discovered in Qinglongshan (Qinglong mountain), Yunyang District, Shiyan, Hubei Province (Zhou, 1998). Through conservation efforts, thousands of these eggs are now semi-exposed in situ within their original stratigraphic layers. Most eggs exhibit minimal deformation, preserved as intact three-dimensional structures. Their unique arrangement and well-defined nesting patterns indicate limited post-depositional disturbance, while the continuous egg-bearing section reveals dozens of fossilized egg layers. A preliminary study by Zhang et al. (2018) classified the majority of Qinglongshan eggs as a single oospecies, Placoolithus tumiaolingensis, which belongs to the oofamily Dendroolithidae—a group characterized by highly porous egg-shells with branched eggshell units. However, the dinosaur species responsible for laying these eggs remains unidentified. Thus, Qinglongshan represents an understudied dinosaur nesting site, offering critical insights into dinosaur reproductive behavior and the Late Cretaceous climate, environmental dynamics, and biotic evolution in China’s interior regions.
Dinosaur egg dating generally relies on indirect methods, as fossilized eggs often lack sufficient radioactive isotopes for direct dating. Constraints are achieved by dating volcanic rocks or ash layers around the eggs using U-Pb or K-Ar/Ar-Ar methods to determine the age of zircon and feldspar. Relative dating methods like biostratigraphy are also used, comparing other fossils in the same rock layer with global stratigraphic profiles to estimate the eggs’ age. Paleomagnetic dating helps identify the stratum and constrain the eggs’ age (e.g., Li et al., 2010 used magnetostratigraphy to show that the Xixia Basin dinosaur eggs are no later than 83 Ma). However, these methods have indirect errors, such as volcanic eruptions occurring before or after the eggs, or surrounding minerals being affected by later geological processes.
Similarly, dinosaur bone dating faces similar challenges. But advances in carbonate U-Pb absolute dating have enabled in-situ dating of dinosaur bones. Qi et al. (2024) used LA-ICP-MS to U-Pb date early diagenetic calcite in Jurassic sauropod bone cavities from the Sichuan Basin, South China, obtaining an age of 165.3 ± 3.6/5.6 Ma, consistent with the maximum depositional age of 165.8 ± 1.0 Ma from detrital zircons in surrounding rocks, indicating rapid post-mortem diagenesis.
Nevertheless, the absence of reliable chronostratigraphic data for the egg-bearing horizons at Qinglongshan has significantly hindered regional stratigraphic correlation and sedimentological analysis. To address this gap, our study employs LA-MC-ICP-MS U-Pb dating on calcite samples recently identified within the dinosaur eggs. The results aim to establish a robust chronological framework and enhance the comprehensive understanding of the temporal and environmental context of this significant dinosaur egg assemblage.
2 Geological setting and sample
The east-west trending Qinling Orogenic Belt traversing central China has under-gone three major tectonic evolutionary stages since the Neoproterozoic: ocean-continent plate subduction orogeny, continent-continent plate subduction-collision orogeny, and intracontinental orogeny (Zhang et al., 2019.1). From the Late Jurassic to the Cretaceous, the Qinling Orogenic Belt experienced extensional deformation that propagated from its core to the margins. Localized extension along pre-existing NWW-trending faults formed a series of faulted basins such as Xixia, Xichuan, and Yunyang (Figure 1). These basins were filled with thick, predominantly coarse-clastic deposits comprising alluvial fan, fan-delta, and lacustrine facies sediments (Liu and Zhang, 2008.1).
FIGURE 1
The Qinglongshan area, located in the western part of the Yunyang Basin, is dominated by red terrigenous clastic continental deposits primarily composed of alluvial fan facies. These deposits unconformably overlie Precambrian metamorphic rocks. Guan et al. (1997) subdivided this red-bed sequence into three lithological units from bottom to top (Figure 1D). The lower unit is distinguished from the middle and upper units by its composition of breccias, breccia-bearing siltstones to fine sandstones, and abundant dinosaur egg fossils, the dinosaur eggs collected in this study were obtained from this stratum. Zhou et al. (1998) assigned the lower unit to the Late Cretaceous based on dinosaur egg fossil studies, correlating it with the Gaogou Formation in the Xichuan (Xixia) Basin. According to Guan et al. (1997) and Zhou et al. (1998), the Yunyang Qinglongshan Formation and the Gaogou Formation in the Xixia Basin are equivalent. Pan et al. (2007) identified the Xixia Basin as the Late Cretaceous Coniacian (89.8–86.3 Ma) through dinosaur egg fossils, small dinosaur bone fossils, and some fossil fragments of bivalves, gastropods, ostracods, charophytes, plant pollen, and plant fossils. However, the parataxonomic validity of reported oogenera such as Faveoloolithus, Dictyoolithus, and Prismatoolithus has been questioned (Zhao et al., 2015), and issues persist in the subdivision of Dendroolithidae (Zhang et al., 2018).
(A) Spatial distribution of Cretaceous basins in the Qinling Orogen (modified after Chen and Santosh, 2014; Dong et al., 2021). (B) Simplified geological map of Yunyang area. (C) Simplified geological map of Qinglongshan area. (D) Stratigraphic column of Qinglongshan region, the Upper Cretaceous is divided into three groups (modified after Guan et al., 1997). The dinosaur egg samples were collected from the lower Gr.
The carbonate samples in this study were collected from a calcite-filled dinosaur egg fossil preserved at Site No. 1 of the Tumiaoling Dinosaur Egg Fossil Locality in Qinglongshan. The sample consists of monomineralic calcite with well-developed crystals and coarse grain size. The sampled egg is embedded within breccia-bearing siltstone of the lower unit and forms part of a large clutch containing 28 eggs. The morphological characteristics of these eggs and the clutch align closely with Placoolithus tumiaolingensis as described by Zhang et al. (2018). The sampled oblate-spheroid egg shows consistent morphology with others in the clutch, displaying regular spacing without evidence of compressive deformation (Figure 2A). Two additional eggs in the clutch also exhibit calcite infilling. While the sampled egg suffered partial shell damage during collection, the other two calcite-filled eggs retain nearly intact external shells and contain no mixed sediments or shell fragments internally. In contrast, the remaining 26 eggs in the clutch show varying degrees of shell fragmentation, with some retaining only the lower approximately 1/2–3/4 of their shells. Their interiors are filled with breccia-bearing siltstone containing shell fragments, lithologically identical to the host rock (Figures 1A, 2B). These observations suggest that the calcite crystallization process occurred under conditions of intact eggshell preservation, likely postdating or contemporaneous with the fossilization of the dinosaur eggs. The sampling criteria were as follows: the outer surface of the dinosaur eggshell was highly intact, and inside the egg, there were almost no other mixed sediments or eggshell fragments except for calcite crystals, mainly based on purity and homogeneity. In addition, since the dinosaur egg preservation site has been built into a museum, we only collected two fragments from a broken dinosaur egg according to the above principles (Zhang et al., 2018).
FIGURE 2
Calcite dating samples from the eggs. (A) Sampled dinosaur egg fossil; (B) Egg clutch containing the sampled dinosaur egg fossil (red arrow indicates the egg fossil sampled in this study; blue arrows mark two additional calcite-filled egg fossils within the clutch).
The emended oogenus Placoolithus is characterized by the following unique combination of characters: oblate egg shape; an equatorial plane circular or sub-circular with long axis of 120–170 mm and short axis of 117–159 mm (Figure 2); eggshell thickness of 1.31–2.40 mm. Moreover, symmetric or asymmetric branches of eggshell unit usually appear in the middle part of the eggshell, and occasionally near the outer surface of the eggshell (Zhang et al., 2018). The eggshell units of the eggs usually contain two symmetrical branches. Most of the eggshell units branch in the middle part of the eggshell, while the others divide near the inner surface of the eggshell. Sometimes, one of the two branches subdivides into two smaller branches near the outer surface of eggshell (Figure 3).
[…]
FIGURE 3
Photos of dinosaur eggshell under the microscope. The eggshell unit is slender and symmetrical (rarely asymmetrical), and is divided into two branches in the middle part of the eggshell. The compact layer accounts for 1/10–1/4 of the eggshell.
Chen Q, Cheng X, Wang J, Zhao B, Zhang S, Ning Y, Wang G, He K, Zhang W, Yu D, Li J, Zou Y, Chen G, Li M and Cheng H (2025)
Geological age of the Yunyang dinosaur eggs revealed by in-situ carbonate U-Pb dating and its scientific implications.
Front. Earth Sci. 13:1638838. doi: 10.3389/feart.2025.1638838
Copyright: © 2025 The authors.
Published by Frontiers Media S.A. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
The chronology revealed by these eggs is, of course, a major problem for creationists. At around 85 million years old, they sit squarely in the Late Cretaceous, tens of millions of years before the end-Cretaceous extinction event and more than four orders of magnitude older than the young-Earth timeline allows. For anyone committed to the idea that Earth and all life were conjured into being just a few thousand years ago, the data are not merely awkward but completely irreconcilable.
The inevitable fallback argument is that radiometric clocks must once have ticked faster—that radioactive decay rates have somehow changed. But this claim is implausible on both physical and observational grounds. The half-lives of uranium isotopes are determined by fundamental forces within the atomic nucleus. To accelerate those decay rates by a factor of a million or more, as creationists would require, would mean wholesale changes to nuclear physics itself. Such changes would release cataclysmic amounts of energy, enough to vaporise the Earth’s crust many times over. No such event is recorded in geology, ice cores, or human history.
Even more tellingly, if decay rates had varied so drastically, atoms themselves could not have formed stably in the first place—precisely at the point in cosmic history when creationists insist their god was “fine-tuning” the universe for life. Their supposed solution to the problem of radiometric dating would, in effect, make chemistry, stars, planets, and living organisms impossible.
Moreover, decay rates are not assumed; they are directly measured in the laboratory and checked continuously against natural “clocks” in minerals. Independent methods—from uranium–lead to potassium–argon to luminescence dating—consistently converge on the same vast timescales. If decay rates had varied, these different clocks would disagree wildly, yet they do not. Instead, they paint a coherent and self-consistent picture of deep time.
So the eggs from Tumiaoling are not just a fascinating glimpse into dinosaur reproduction; they are also another robust reminder that Earth’s history is measured in billions, not thousands, of years. Creationists can deny, dismiss, or distort, but the evidence remains—layer upon layer, fossil upon fossil, isotope upon isotope—an overwhelming record of a deep past that their worldview simply cannot accommodate.
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