A collection of dinosaur teeth hailing back to the Cretaceous and Jurassic periods has given scientists a new window into the world's prehistoric climate.
By studying an isotope of oxygen in the fossils to infer atmospheric carbon dioxide levels, a team led by geochemist Dingsu Feng of the Georg August University of Göttingen in Germany has reconstructed the very air the dinosaurs breathed.
The results show that dinosaur teeth are a powerful tool for scientists, not just for understanding the world in which the dinosaurs lived, but the events that took place, since changing isotope levels can imply events such as massive volcanic eruptions.
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"Our findings provide a new research avenue to reconstruct a direct link between land-living vertebrates and the atmosphere they breathed," paleontologist and geochemist Thomas Tütken of the Institute of Geosciences at Johannes Gutenberg Universität, Mainz in Germany told ScienceAlert.
"Even after up to 150 million years, isotopic traces of the oxygen molecules of the Mesozoic atmosphere that the dinosaur inhaled are still preserved in fossil tooth enamel and can tell us something about the ancient atmosphere composition and global photosynthetic biomass production."
You don't just exist in this beautiful world of ours. It also exists in you. Everything you take in – from the food you eat, to the liquid you drink, to even the very air that you breathe – leaves a chemical imprint on your body, including your bones and teeth.
This is true for all vertebrates, including the dinosaurs. Ratios of atoms of the same elements but different masses, known as isotopes, can hint at a variety of ecological and climatic variations that dominate in an organism's lifetime.
Oxygen atoms attached to carbon dioxide is just one such isotope. In particular, Feng and her team looked for tracers of an isotope called oxygen-17. Processes in the atmosphere result in a lower amount of this particular isotope in the dioxide oxygen gas that is then inhaled by living organisms.
"Air-breathing vertebrates incorporate a fraction of this anomalous air oxygen into their body water pool due to oxidative metabolism of food," Tütken explained.
"A fraction of this oxygen isotope anomaly is incorporated during biomineralization processes into dental enamel, and survives over millions of years in this vertebrate high tissue and can thus be used to infer past atmospheric CO2 levels."
The researchers recently demonstrated that oxygen isotope ratios in the tooth enamel of living, modern animals provide an accurate representation of atmospheric CO2 levels. The next logical step was then to see if they could do the same thing with fossils that are millions of years old.
"Dinosaur tooth samples were prime targets to be analyzed as large triple oxygen isotope anomalies were to be expected and could quite precisely be measured," Tütken said.
Using enamel powders previously taken from specimens obtained from museum collections across Europe for other diet-related reconstructions, Tütken and his colleagues concluded concentrations of CO2 had been high during the Mesozoic; a finding in agreement with previous investigations into Earth's CO2 history.
In the late Jurassic, CO2 levels were at about 1,200 parts per million, for example; in the late Cretaceous, around 750 parts per million. By comparison, Earth's atmosphere currently has around 430 parts per million CO2, and counting.
During the Mesozoic, atmospheric CO2 was probably produced by much higher levels of volcanic activity than we see today. Two teeth, in particular, seemed to suggest a spike in volcanic activity.
"There were surprising high triple oxygen isotope anomalies found for one T. rex and one sauropod (Kaatedocus) tooth analyzed compared to the other near-contemporaneous dinosaurs," Tütken said.
"These potentially reflect atmospheric spikes of high CO2 levels during the time these individual dinosaurs were alive. Most likely related to volcanic CO2 emission during large flood basalt eruption events. Thus our study provides new insights into the composition of the Mesozoic atmosphere in which the dinosaurs breathed and indicates that CO2 levels fluctuated (up to 160 percent) over geologically short time scales."
Now that the team has shown their technique works, they plan to look at teeth from an event known as the Great Dying, the Permian-Triassic global extinction that took place 252 million years ago and wiped out the vast majority of all animals on Earth. This event has been linked to a devastating period of volcanic activity that wrapped our planet in a volcanic shroud for millions of years.
By reconstructing the atmospheric CO2 from this period, the researchers hope to learn more about how the Great Dying impacted life on Earth.
The research has been published in the Proceedings of the National Academy of Sciences.