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Dip in Carbon Dioxide May Have Helped Dinosaurs Walk from Brazil to Greenland

The new evidence rewrites the timeline of dinosaurs’ migration across two continents.

The new evidence rewrites the timeline of dinosaurs’ migration across two continents.

A cliff in Jameson Land Basin in central East Greenland, the northernmost site where sauropodomorph fossils are found. The labels point out several series of layers that helped the researchers precisely date the oldest sauropodomorph fossils in North America. (Photo by Lars Clemmensen)

(CN) — Scientists have discovered new evidence indicating a massive dip in atmospheric carbon dioxide enabled dinosaurs to migrate from South America to Greenland.

In their study, published Monday in the journal Proceeding of the National Academy of Sciences, Dennis Kent, an adjunct research scientist at Columbia University's Lamont-Doherty Earth Observatory, and Lars Clemmensen from the University of Copenhagen discuss their findings and likely theories.

The sauropodomorphs were a group of giant, long necked, herbivorous dinosaurs with small skulls and leaf-shaped teeth. To this day, dinosaurs from this clade, including the brontosaurus and the brachiosaurus, were the largest animals that have ever walked the earth. Their fossils can be found all around the world on every continent including Antarctica — meaning these highly mobile giants were able to live in vastly diverse environments. 

Scientists have generally believed that between 225 and 205 million years ago, these dinosaurs settled down in Greenland, but the findings in Monday’s study refute that. To investigate this timeline, the team revisited various fossil sites in South America, Arizona, New Jersey, Europe and Greenland where sauropodomorphs were discovered. They combed through the layers of the rocks analyzing the magnetic patterns, which are recordings of the magnetic field at the time of the rock’s formation.

A claw of a bipedal sauropodomorph (Plateosaurus) from the Jameson Land site in East Greenland. Parts of the animal were found in 1995 by Farish Jenkins (Harvard), Neil Shubin (U Penn), Lars Clemmensen (Copenhagen), and others. It is the oldest known specimen in the area. (Photo by Dennis Kent)

The rock patterns revealed sauropodomorphs actually arrived in Greenland approximately 214 million years ago, which would put their migration at the time when today’s continents made up one supercontinent known as Pangea.

But the discovery filled in one blank and revealed another one. Sauropod fossils have been found in Argentina and Brazil dating back to 230 million years ago, and even though 6,500 miles separate South American and Greenland it wouldn’t have taken the creatures millions of years to travel there, leaving the authors to wonder what took so long and why.

"In principle, the dinosaurs could have walked from almost one pole to the other," Kent said in a statement accompanying the study. "There was no ocean in between. There were no big mountains. And yet it took 15 million years. It's as if snails could have done it faster."

Kent added that if a herd of sauropods only traveled a single mile a day, it would still take less than 20 years for them to walk from South America to Greenland.

In their search for answers, they discovered a curious climate event occurring around the same time the dinosaurs would have arrived in Greenland. Earth’s carbon dioxide levels in the Triassic period 215 million years ago were incredibly high —an estimated 4,000 parts per million, which the authors note is a staggering 10 times higher than today even with climate change. However, over the next 3 million years, the atmosphere saw a huge drop in CO2 levels, slashed in half to 2,000 parts per million.

The authors hypothesized this dip in CO2 levels likely had something to do with the timing of the sauropod migration. The previous high levels could have made it difficult for the herds to travel out of South America, and they suspect the removal of half the Earth’s CO2 had immense impacts on the environment and probably made the journey less treacherous.

They elaborate that if conditions are more tropical around the equator and dryer at higher latitudes, it would make sense that an abundance of CO2 in the atmosphere would exacerbate those conditions. The two climates could have been too drastically opposite for the sauropods to weather, and therefore too dangerous for migration.

"We know that with higher CO2, the dry gets drier and the wet gets wetter," said Kent.

Before the drop in CO2, crossing into dryer regions for an extended amount of time would have been incredibly dangerous for the herbivores, who needed to eat over 1,000 pounds of vegetation every day. On the other hand, the wet regions may have been experiencing dramatic rainfall and storms that would also have made migrating dangerous. The authors note that there isn’t much that points to these dinosaurs leaving the safety of temperate South America.

After the drop, they believe conditions leveled out, making both tropical and dry regions more habitable. Furthermore, the sauropods may have had help as passageways like rivers and lakes would have provided sustenance along the way. Once they made it to Greenland, the climate was similar to New York, without the harsh winters, making it ideal for them to thrive.

Fossil records show they passed through the dryer areas but did not settle down for long. In Greenland however, body fossils are abundant and point to a prolonged stay.

"Once they arrived in Greenland, it looked like they settled in,'" said Kent. "They hung around as a long fossil record after that."

The authors emphasize their paper outlines a theory, and while it is very likely that the lack of CO2 aided the sauropodomorphs, it is not concrete yet. Moving forward, Kent plans to study the decline, investigating what caused it and why.

“The idea that a dip in CO2 could have helped these dinosaurs to overcome a climatic barrier is speculative but plausible, and it seems to be supported by the fossil record,” said Kent.

Map shows how the major continents were arranged 220 million years ago in the Pangea supercontinent. "Isch" and "P" mark locations with sauropodomorph fossils up to 233 million years old. The herbivorous dinosaurs didn't reach Jameson Land in Greenland ("JL") until about 214 million years ago. (Image by Dennis Kent and Lars Clemmensen)
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