Dinosaur teeth serve as ‘climate time capsules,’ unlocking secrets of Earth’s ancient greenhouse climate

A previously unexploited source of information is now throwing new light on Earth’s climate during the age of dinosaurs. Fossilized dinosaur teeth show that concentrations of carbon dioxide in the atmosphere during the Mesozoic Era, i.e., 252 to 66 million years ago, were far higher than they are today. This has been determined by researchers at the universities in Göttingen, Mainz, and Bochum following the analysis of oxygen isotopes in the dental enamel of dinosaur teeth.

The scientists used a new innovative method to detect the relative ratios of all three natural oxygen isotopes, opening new prospects for geological climate research. In addition, the isotope data shows that the primary production of all plants at the time was double that of the current yield. This probably contributed to a climate that was particularly dynamic when dinosaurs roamed Earth. The results of the research project have been published recently in the journal Proceedings of the National Academy of Sciences.

The team of researchers investigated the tooth enamel of dinosaur teeth found in North America, Africa and Europe and dating back to the late Jurassic and the late Cretaceous periods. Tooth enamel is one of the most stable biological materials. It contains three isotopes of the oxygen that a dinosaur would have inhaled with the air during respiration.

The ratios of individual isotopes in airborne oxygen are determined by changes in atmospheric carbon dioxide levels and the photosynthetic activity of vegetation. The resultant connection means that dinosaur teeth can be used to draw conclusions with regard to the nature of the climate and vegetation during the dinosaur age.

During the Late Jurassic, roughly 150 million years ago, the atmosphere contained a concentration of carbon dioxide (CO₂) four times that in the period before industrialization commenced, i.e., before human activity resulted in the release of large quantities of greenhouse gases into the air. Some 73 to 66 million years ago, in the Late Cretaceous, the corresponding concentration of CO₂ was three times higher than the preindustrial level.

The team discovered that certain teeth of Tyrannosaurus rex and Kaatedocus siberi contained unusual combinations of oxygen isotopes. This might be evidence of peaks of CO₂ levels in the air that could be attributable to volcanic activity, such as the massive eruptions that occurred in what is now India in the flood basalt region of the Deccan Traps at the end of the Cretaceous period. That the land and aquatic vegetation was more photosynthetically active in global terms can also probably be ascribed to the levels of CO₂ and the higher average annual temperatures.

The new results represent a breakthrough in paleoclimatology. To date, researchers have mainly used soil carbonates and so-called marine proxies to reconstruct the climate of the past. Marine proxies are indirect indicators present in marine environments that correlate so closely with the parameters under investigation that they represent surrogates for these.

Unfortunately, the results obtained are subject to uncertainty. By analyzing the three oxygen isotopes in fossilized teeth, the researchers have developed the first method focusing on land-based vertebrates.

“Our method provides us with completely new insights into Earth’s past,” stated the lead author of the paper, Dr. Dingsu Feng of the Geochemistry and Isotope Geology Department of the University of Göttingen. “We now have the possibility to use fossilized tooth enamel to study the composition of the atmosphere of the early Earth and the productivity of terrestrial and marine vegetation back then. This is crucial for our understanding of long-term climate dynamics.”

As Feng points out, dinosaurs are becoming climate experts: “Their teeth recorded the climate more than 150 million years ago—and at last we are able to read that record.”

“The information obtained through our study on the global primary production provides important evidence of both marine and terrestrial food webs that would otherwise be difficult to obtain, as the available plant biomass limits the abundance and number of species and the length of food chains in the ecosystem,” emphasized co-author Professor Dr. Eva M. Griebeler of the JGU Institute of Organismic and Molecular Evolution.

And JGU paleontologist Professor Dr. Thomas Tütken, also co-author of the article, added, “The analysis of the three oxygen isotopes in dental enamel allows us to also measure the proportions of oxygen assimilated with respiratory air and drinking water. This provides us with greater understanding of the physiology and paleobiology of dinosaurs but can equally be used for the study of other vertebrate species.”

Hence, the quantification of the three oxygen isotopes in the dental enamel of land-based vertebrates provides new insights into changes to the composition of the atmosphere and into the climatic and environmental conditions throughout the history of our planet.