CO2 immersion may have helped dinosaurs to move from South America to Greenland

A new paper refines estimates of when herbivorous dinosaurs had to traverse North America on a northern trek to reach Greenland, pointing to an interesting climatic phenomenon that may have helped them during the trip.

The study, conducted today in Proceedings of the National Academy of Sciences, was written by Dennis Kent, supplementary research scientist at the Lamont-Doherty Earth Observatory of Columbia University, and Lars Clemmensen of the University of Copenhagen.

Previous estimates suggest that sauropodomorphs – a group of long-necked, herbivorous dinosaurs that eventually included Brontosaurus and Brachiosaurus – arrived in Greenland between 225 and 205 million years ago. But by closely matching ancient magnetism patterns in rock layers at fossil sites in South America, Arizona, New Jersey, Europe, and Greenland, the new study provides a more accurate estimate: it suggests that sauropodomorphs in present-day Greenland reached about 214 million years ago. back. At that time, the continents were all merged to form the supercontinent Pangea.

With this new and more accurate estimate, the authors faced a different question. Fossil records show that sauropodomorphic dinosaurs first appeared in Argentina and Brazil about 230 million years ago. Why then did it take them so long to expand to the Northern Hemisphere?

“In principle, the dinosaurs could have walked from almost one pole to another,” Kent explained. “There was no ocean in between. There were no big mountains. And yet it took 15 million years. It’s like snails could do it faster.” He calculates that if a dinosaur herd walks only one kilometer a day, it will take less than 20 years to undertake the journey between South America and Greenland.

Remarkably, the earth was in the midst of a tremendous dip in atmospheric CO₂ right around the time that the sauropodomorphs would migrate 214 million years ago. Until about 215 million years ago, the Triassic period experienced exceptionally high CO₂ levels, about 4,000 parts per million – about ten times higher than today. But between 215 and 212 million years ago, the CO₂ concentration halved and dropped to about 2000 ppm.

Although the timing of these two events – the declining CO₂ and the migration of sauropodomorphs – may be purely coincidental, Kent and Clemmensen think they may be related. In the paper, they suggest that the lighter levels of CO₂ may have helped remove climate barriers that captured the sauropodomorphs in South America.

On Earth, areas around the equator are hot and humid, while adjacent areas at low latitudes are very dry. Kent and Clemmensen say that on a planet laden with CO₂, the differences between those climate belts may have been extreme – perhaps too extreme to cross the sauropodomorphic dinosaurs.

“We know this with higher CO₂, the drier gets drier and the wet gets wetter, “Kent said. 230 million years ago, the high CO₂ conditions could have made the arid belts too dry to support the movements of large herbivores that must eat a lot of vegetation to survive. Also, the tropics were possibly confined to rainy, monsoon-like conditions that may not have been ideal for sauropodomorphs. There is little evidence that they have ventured into the temperate, medium-sized habitats to which they have adapted in Argentina and Brazil.

But when the CO₂ levels dropped 215-212 million years ago, perhaps the tropical regions became softer and the arid regions became less arid. There were possibly passages, such as along rivers and strings of lakes, that would help sustain the herbivores during the 6,500-mile journey to Greenland, where their fossils are now abundant. At the time, Greenland would have had a temperate climate similar to the New York State’s climate, but with much milder winters, because there were no ice sheets at the time.

“After they arrived in Greenland, it looked like they were going to live there,” Kent said. “They then hung around like a long fossil record.”

The idea of ​​a dip in CO₂ could these dinosaurs have helped overcome a climate barrier is speculative but plausible, and it appears to be supported by the fossil record, Kent said. Sauropodomorphic body fossils were not found in the tropical and arid regions of this period – although their footprints occasionally appear – indicating that they did not reside in those areas.

Kent then hopes to continue to better understand the big CO₂ dip, including what caused it and how fast CO₂ levels dropped.