The atmosphere of Earth during the Mesozoic era, between 252 and 66 million years ago, contained far more carbon dioxide than it does today and total photosynthesis from plants around the world was twice as high as it is today, according to an analysis of oxygen isotope composition of dinosaur teeth.
The fossilized teeth of Camarasaurus from the Morrison Formation in the United States. Image credit: Sauriermuseum Aathal.
In the study, Dr. Dingsu Feng from the University of Göttingen and colleagues analyzed the dental enamel of dinosaurs that lived in North America, Africa and Europe during the Late Jurassic and Late Cretaceous periods.
“Enamel is one of the most stable biological materials,” they said.
“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 us 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 dinosaur species — Tyrannosaurus rex and Kaatedocus siberi — contained a strikingly unusual composition of oxygen isotopes.
This points to carbon dioxide 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 carbon dioxide 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.
“Our method gives us a completely new view of the Earth’s past,” Dr. Feng said.
“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. Long ago their teeth recorded the climate for a period of over 150 million years — finally we are getting the message.”
The study was published August 4, 2025 in the Proceedings of the National Academy of Sciences.
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Dingsu Feng et al. 2025. Mesozoic atmospheric CO2 concentrations reconstructed from dinosaur tooth enamel. PNAS 122 (33): e2504324122; doi: 10.1073/pnas.2504324122