An intriguing weather phenomenon that reduced CO2 in the atmosphere could help dinosaurs cover the distance between present-day South America and Greenland, a study in PNAS reveals.Previous estimates suggested that sauropodomorphs, a group of long-necked herbivorous dinosaurs that eventually included brontosaurs and brachiosaurs, arrived in Greenland sometime between 225 and 205 million years ago.
But by painstakingly 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 appeared in what is now Greenland around around 12 years ago. 214 million years.
At that time, all the continents came together, forming the supercontinent Pangea.
With this new and more precise estimate, the authors were faced with another question. Fossil records show that sauropodomorphic dinosaurs first appeared in Argentina and Brazil about 230 million years ago. So why did it take them so long to expand to the Northern Hemisphere?
“In principle, dinosaurs could have walked from almost one pole to the other,” Dennis Kent, deputy research scientist at the Lamont-Doherty Earth Observatory at Columbia University, explained in a statement, along with Lars Clemmensen, from the University of Copenhagen, in Denmark.
“There was no ocean in between. There were no big mountains. And yet it took 15 million years. It’s as if the snails could have done it faster,” he adds. He estimates that if a herd of dinosaurs walked just one mile a day, it would take them less than 20 years to make the journey between South America and Greenland.
Interestingly, Earth was in the midst of a tremendous drop in atmospheric CO2 just at the time that sauropodomorphs would have been migrating 214 million years ago.
Until about 215 million years ago, the Triassic period had experienced extremely high CO2 levels, around 4,000 parts per million, about 10 times higher than today. But between 215 and 212 million years ago, the concentration of CO2 was cut in half, dropping to about 2,000 ppm.
Although the timing of these two events, the drop in CO2 and the migration of the sauropodomorphs, could be pure coincidence, Kent and Clemmensen believe they may be related. In the paper, they suggest that the milder levels of CO2 may have helped to remove the climatic barriers that may have trapped sauropodomorphs in South America.
On Earth, the areas around the equator are hot and humid, while adjacent areas at low latitudes tend to be very dry. Kent and Clemmensen say that on a CO2-overloaded planet, the differences between those climate belts may have been extreme, perhaps too extreme for sauropodomorph dinosaurs to cross.
“We know that with more CO2, the dry becomes drier and the humid becomes wetter,” notes Kent. 230 million years ago, high CO2 conditions could have made arid belts too dry to support 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 ventured from the temperate mid-latitude habitats to which they adapted in Argentina and Brazil.
But when CO2 levels dropped 215-212 million years ago, perhaps tropical regions became milder and arid regions became less dry.
It is possible that there were some corridors, such as along rivers and lake chains, that would have helped support the herbivores along the 10,500-kilometer journey to Greenland, where their fossils now abound.
Back then, Greenland would have had a temperate climate similar to the current New York state climate, but with much milder winters, because there were no polar ice caps at the time.
“Once they got to Greenland, it seemed like they had settled,” Kent says. “After that, they remained as one long fossil record.”
The idea that a drop in CO2 could have helped these dinosaurs overcome a climate barrier is speculative but plausible, and appears to be supported by the fossil record, Kent notes.
No sauropodomorph body fossils have been found in the tropical and arid regions of this time period, although their tracks appear occasionally, suggesting that they did not remain in those areas.
Now, Kent hopes to keep working to better understand the big drop in CO2, including the causes and how quickly CO2 levels dropped.
I’m a science journalist and host of Cosmic Controversy (brucedorminey.podbean.com) as well as author of “Distant Wanderers: the Search for Planets Beyond the Solar System.” I primarily cover aerospace and astronomy. I’m a former Hong Kong bureau chief for Aviation Week & Space Technology magazine and former Paris-based technology correspondent for the Financial Times newspaper who has reported from six continents. A 1998 winner in the Royal Aeronautical Society’s Aerospace Journalist of the Year Awards (AJOYA), I’ve interviewed Nobel Prize winners and written about everything from potato blight to dark energy. Previously, I was a film and arts correspondent in New York and Europe, primarily for newspaper outlets like the International Herald Tribune, the Boston Globe and Canada’s Globe & Mail. Recently, I’ve contributed to Scientific American.com, Nature News, Physics World, and Yale Environment 360.com. I’m a current contributor to Astronomy and Sky & Telescope and a correspondent for Renewable Energy World. Twitter @bdorminey