Dinosaur teeth give glimpse of early Earth’s climate
New method reconstructs carbon dioxide levels and photosynthesis from fossilized tooth enamel
image:
Tooth of a Europasaurus, a dinosaur similar to Diplodocus, in limestone, found in the Langenberg quarry in the Harz Mountains which was also analysed in the study.
view moreCredit: Thomas Tütken
A previously untapped source of data sheds new light on the climate of the early Earth: fossilized dinosaur teeth show that the atmosphere during the Mesozoic era, between 252 and 66 million years ago, contained far more carbon dioxide than it does today. An international research team at the Universities of Göttingen, Mainz and Bochum made this discovery by analysing oxygen isotopes in tooth enamel. They used a newly developed method that opens up opportunities for research into the Earth's climate history. In addition, the researchers found that total photosynthesis from plants around the world was twice as high as it is today. This probably contributed to the dynamic climate during the time of the dinosaurs. The results were published in the journal PNAS.
The research team analysed the enamel of dinosaur teeth found in North America, Africa and Europe dating from the late Jurassic and late Cretaceous periods. Enamel is one of the most stable biological materials. It records different isotopes of oxygen that the dinosaurs inhaled with every breath that they took. The ratio of isotopes in oxygen is affected by changes in atmospheric carbon dioxide and photosynthesis by plants. This correlation allows researchers to draw conclusions about the climate and vegetation during the age of the dinosaurs.
In the late Jurassic period, around 150 million years ago, the air contained around four times as much carbon dioxide as it did before industrialization – that is, before humans started emitting large quantities of greenhouse gases into the atmosphere. And in the late Cretaceous period, around 73 to 66 million years ago, the level was three times as high as today. Individual teeth from two dinosaurs – Tyrannosaurus rex and another known as Kaatedocus siberi which is related to Diplodocus – contained a strikingly unusual composition of oxygen isotopes. This points to CO₂ spikes that could be linked to major events such as volcanic eruptions – for example, the massive eruptions of the Deccan Traps in what is now India, which happened at the end of the Cretaceous period. The fact that plants on land and in water around the world were carrying out more photosynthesis at that time was probably associated with CO₂ levels and higher average annual temperatures.
This study marks a milestone for paleoclimatology: until now, carbonates in the soil and “marine proxies” were the main tools used to reconstruct the climate of the past. Marine proxies are indicators, such as fossils or chemical signatures in sediments, that help scientists understand environmental conditions in the sea in the past. However, these methods are subject to uncertainty. By analysing oxygen isotopes in tooth fossils, the researchers have now developed the first method that focuses on vertebrates on land. “Our method gives us a completely new view of the Earth's past,” explains lead author Dr Dingsu Feng at the University of Göttingen’s Department of Geochemistry. “It opens up the possibility of using fossilized tooth enamel to investigate the composition of the early Earth's atmosphere and the productivity of plants at that time. This is crucial for understanding long-term climate dynamics.” Dinosaurs could be the new climate scientists, according to Feng: “Long ago their teeth recorded the climate for a period of over 150 million years – finally we are getting the message.”
The study was funded by the German Research Foundation (DFG) and by the VeWA consortium as part of the LOEWE programme of the Hessisches Ministerium für Wissenschaft und Forschung, Kunst und Kultur.
Original publication: Dingsu Feng, Thomas Tütken, Eva Maria Griebeler, Daniel Herwartz & Andreas Pack. Mesozoic atmospheric CO2 concentrations reconstructed from dinosaur tooth enamel. Proceedings of the National Academy of Sciences (PNAS) (2025). DOI: 10.1073/pnas.2504324122
Tooth of a Tyrannosaurus rex – like the teeth analysed in this study – found in Alberta, Canada
Credit
Thomas Tütken
Teeth of a Camarasaurus, found in the Morrison Formation, USA, which were also analyzed in the research.
Credit
Sauriermuseum Aathal
Journal
Proceedings of the National Academy of Sciences
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Mesozoic atmospheric CO2 concentrations reconstructed from dinosaur tooth enamel.
Article Publication Date
24-Aug-2025
Rising deep-ocean oxygen levels opened up new marine habitats, spurred speciation
Duke University
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An artist’s rendering of a prehistoric jawed fish from the Late Devonian called Dunkleosteus. These sorts of large, active vertebrates evolved shortly after the deep ocean became well-oxygenated. © 2008 N. Tamura/CC-BY-SA
view moreCredit: © 2008 N. Tamura/CC-BY-SA
Some 390 million years ago in the ancient ocean, marine animals began colonizing depths previously uninhabited. New research indicates this underwater migration occurred in response to a permanent increase in deep-ocean oxygen, driven by the aboveground spread of woody plants — precursors to Earth’s first forests.
That rise in oxygen coincided with a period of remarkable diversification among fish with jaws — the ancestors of most vertebrates alive today. The finding suggests that oxygenation might have shaped evolutionary patterns among prehistoric species.
“It’s known that oxygen is a necessary condition for animal evolution, but the extent to which it is the sufficient condition that can explain trends in animal diversification has been difficult to pin down,” said co-lead author Michael Kipp, assistant professor of earth and climate sciences in the Duke University Nicholas School of the Environment. “This study gives a strong vote that oxygen dictated the timing of early animal evolution, at least for the appearance of jawed vertebrates in deep-ocean habitats.”
For a time, researchers thought that deep-ocean oxygenation occurred once at the beginning of the Paleozoic Era, some 540 million years ago. But more recent studies have suggested that oxygenation occurred in phases, with nearshore waters first becoming livable to breathing organisms, followed by deeper environments.
Kipp and colleagues homed in on the timing of those phases by studying sedimentary rocks that formed under deep seawater. Specifically, they analyzed the rocks for selenium, an element that can be used to determine whether oxygen existed at life-sustaining levels in ancient seas.
In the marine environment, selenium occurs in different forms called isotopes that vary by weight. Where oxygen levels are high enough to support animal life, the ratio of heavy to light selenium isotopes varies widely. But at oxygen levels prohibitive to most animal life, that ratio is relatively consistent. By determining the ratio of selenium isotopes in marine sediments, researchers can infer whether oxygen levels were sufficient to support animals that breathe underwater.
Working with research repositories around the world, the team assembled 97 rock samples dating back 252 to 541 million years ago. The rocks had been excavated from areas across five continents that, hundreds of millions of years ago, were located along the outermost continental shelves — the edges of continents as they protrude underwater, just before giving way to steep drop-offs.
After a series of steps that entailed pulverizing the rocks, dissolving the resulting powder and purifying selenium, the team analyzed the ratio of selenium isotopes that occurred in each sample.
Their data indicated that two oxygenation events occurred in the deeper waters of the outer continental shelves: a transient episode around 540 million years ago, during a Paleozoic period known as the Cambrian, and an episode that began 393-382 million years ago, during an interval called the Middle Devonian, that has continued to this day. During the intervening millennia, oxygen dropped to levels inhospitable to most animals. The team published their findings in Proceedings of the National Academy of Sciences in August.
“The selenium data tell us that the second oxygenation event was permanent. It began in the Middle Devonian and persisted in our younger rock samples,” said co-lead author Kunmanee “Mac” Bubphamanee, a Ph.D. candidate at the University of Washington.
That event coincided with numerous changes in oceanic evolution and ecosystems — what some researchers refer to as the “mid-Paleozoic marine revolution.” As oxygen became a permanent feature in deeper settings, jawed fish, called gnathostomes, and other animals began invading and diversifying in such habitats, according to the fossil record. Animals also got bigger, perhaps because oxygen supported their growth.
The Middle Devonian oxygenation event also overlapped with the spread of plants with hard stems of wood.
“Our thinking is that, as these woody plants increased in number, they released more oxygen into the air, which led to more oxygen in deeper ocean environments,” said Kipp, who began this research as a Ph.D. student at the University of Washington.
The cause of the first, temporary oxygenation event during the Cambrian is more enigmatic.
“What seems clear is that the drop in oxygen after that initial pulse hindered the spread and diversification of marine animals into those deeper environments of the outer continental shelves,” Kipp said.
Though the team’s focus was on ancient ocean conditions, their findings are relevant now.
“Today, there’s abundant ocean oxygen in equilibrium with the atmosphere. But in some locations, ocean oxygen can drop to undetectable levels. Some of these zones occur through natural processes. But in many cases, they’re driven by nutrients draining off continents from fertilizers and industrial activity that fuel plankton blooms that suck up oxygen when they decay,” Kipp said.
“This work shows very clearly the link between oxygen and animal life in the ocean. This was a balance struck about 400 million years ago, and it would be a shame to disrupt it today in a matter of decades.”
Funding: MAK was supported by an NSF Graduate Research Fellowship and Agouron Institute Postdoctoral Fellowship. Additional support was provided by the NASA Astrobiology Institute’s Virtual Planetary Laboratory.
Citation: “Mid-Devonian ocean oxygenation enabled the expansion of animals into deeper-water habitats,” Bubphamanee K., Kipp M., Meixnerová J., Stüeken E., Ivany L, Bartholomew A., Algeo T., Brocks J., Dahl T., Kinsley J., Tissot F., Buick R. Proceedings of the National Academy of Sciences, August 2025, DOI: 10.1073/pnas.2501342122
Journal
Proceedings of the National Academy of Sciences
Method of Research
Experimental study
Subject of Research
Animals
Article Title
Mid-Devonian ocean oxygenation enabled the expansion of animals into deeper-water habitats
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