Dinosaurs take a hike

A new paper pinpoints the date that a large group of dinosaurs made it to Greenland, suggesting that climatic changes may have determined dinosaur migration patterns.

It was previously known that sauropodomorphs – a clade of herbivorous dinosaurs that later evolved into Brontosaurus and Brachiosaurus, among others – first emerged in modern-day South America and then migrated north between 225 and 205 million years ago.

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Key research points

• There was previously a broad window for when sauropodomorphs arrived in the Northern Hemisphere
• New research narrows the date of arrival to 214 million years ago
• This timing coincides with a massive dip in CO₂ levels
• There may have been a change in climate that allowed them to move

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This research narrows that dinosaur migration estimate down to 214 million years ago. The work is published in the Proceedings of the National Academy of Sciences.

Researchers analysed the magnetism patterns in ancient rock layers at fossil sites all across the Americas and Europe, which let them identify when the dinosaurs first appeared in Greenland.

But this discovery gave rise to another mystery: why did it take so long for the dinosaurs to get to the Northern Hemisphere? The sauropodomorphs first appeared in Argentina and Brazil 230 million years ago, and Earth’s land at the time was still mostly connected up into the supercontinent Pangaea.

“In principle, the dinosaurs could have walked from almost one pole to the other,” says Dennis Kent, an author on 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.”

But the new migration date does line up with another dramatic planetary change: a drop in carbon dioxide levels from 4,000 to 2,000 parts per million (or 10–5 times the amount of today’s levels). This would have caused a significant change in climate, which could have allowed the dinosaurs to move through previously uninhabitable areas.

“We know that with higher CO₂, the dry gets drier and the wet gets wetter,” says Kent. He thinks it’s plausible the milder levels opened up passageways through the hot and humid equatorial zone, although the timing may just be a coincidence.

The sauropodomorphs were well-suited to the warmer climate of Greenland at the time. “Once they arrived in Greenland, it looked like they settled in,” says Kent. “They hung around as a long fossil record after that.”