Why did dinosaurs move from South America to Greenland?

An intriguing weather phenomenon that reduces CO2 in the atmosphere could help dinosaurs travel the distance between South America and today’s Greenland, a PNAS study finds.

Earlier estimates suggested that sauropodomorphs, a group of long-necked herbivorous dinosaurs that ultimately included brontosaurs and brachiosaurs, arrived in Greenland between 225 and 205 million years ago.

But by carefully matching patterns of ancient magnetism in rock layers in fossil beds in South America, Arizona, New Jersey, Europe and Greenland, the new study offers a more accurate estimate: It suggests that sauropodomorphs first appeared in what is now Greenland around 12,214 million years ago. At that time, all the continents came together, forming the Pangea supercontinent.

With this new, more precise estimate, the authors were faced with another question. Fossil records show that sauropodomorphic dinosaurs first appeared in Argentina and Brazil around 230 million years ago. So why did it take them so long to expand to the northern hemisphere?

“In principle, the dinosaurs could have walked from pole to pole,” said Dennis Kent, associate researcher at the Lamont-Doherty Earth Observatory at Columbia University, in a statement, with Lars Clemmensen , from the University of Copenhagen, Denmark.

“There was no ocean in between. There were no great mountains. And yet it took 15 million years. It’s like the snails could have done it faster,” he adds. He estimates that if a herd of dinosaurs walked just a mile a day, it would take them less than 20 years to make the trip from South America to Greenland.

Interestingly, Earth was in the midst of a huge drop in atmospheric CO2 just as the sauropodomorphs would have migrated 214 million years ago. Until about 215 million years ago, the Triassic Period had seen extremely high CO2 levels, around 4,000 parts per million, about 10 times higher than today. But 215 to 212 million years ago, the CO2 concentration halved, dropping to around 2,000 ppm.

While the timing of these two events, the drop in CO2 and the migration of sauropodomorphs, may be pure coincidence, Kent and Clemmensen believe they may be related. In the article, they suggest that the milder CO2 levels may have helped break down climate barriers that might have trapped sauropodomorphs in South America.

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

“We know that with more CO2, the dry gets drier and the humidity gets wetter,” notes Kent. 230 million years ago, high CO2 conditions could have made arid belts too dry to withstand the movements of large herbivores that need to eat a lot of vegetation to survive.

The tropics may also have been trapped in monsoon-like rainy conditions that may not have been ideal for sauropodomorphs. There is little evidence that they have ventured outside of the mid-latitude temperate habitats to which they have adapted in Argentina and Brazil.

But when CO2 levels dropped 215 to 212 million years ago, the tropics may have become milder and arid regions became less dry. It is possible that there were corridors, such as along rivers and chains of lakes, that would have helped support herbivores on the approximately 10,500 kilometer journey to Greenland, where their fossils abound. today. Back in the day, Greenland would have had a similar temperate climate to New York State today, but with much milder winters, as there were no polar ice caps at the time.

“Once they got to Greenland, it looked like they had settled down,” Kent says. “After that, they stuck around like a long fossil record.

The idea that a drop in CO2 could have helped these dinosaurs overcome a climate barrier is speculative but plausible, and seems to be supported by the fossil record, notes Kent. No sauropodomorph fossil bodies have been found in the tropics and arid regions of this period, although their traces appear occasionally, suggesting that they did not remain in these areas.

Now Kent hopes to continue working to better understand the sharp drop in CO2, including the causes and how quickly CO2 levels have fallen.