For the first time, researchers have accurately dated the arrival of the first herbivorous dinosaurs in East Greenland.

A new study shows extreme climatic conditions slowed down their trek from the southern hemisphere. Their long walk was only possible because as CO2 levels dropped suddenly, the Earth’s climate became less extreme.

A snail could have crawled its way faster. 10,000 kilometers (6,213 miles) over 15 million years—that’s how long it took the first herbivorous dinosaurs to make their way from Brazil and Argentina. (That’s two feet a year!)  😀

The herbivorous dinosaurs first appeared in Brazil and Argentina roughly 230 million years ago. This was during the early part of the Late Triassic period, the Norian, when the world consisted of one supercontinent called Pangea, without any seas in between. The supercontinent allowed dinosaurs to disperse, unhindered from south to north. So, what took them so long to get to Greenland?

The answer lies in the accurate dating of unique rock deposits consisting of a 350-meter-long (1,148 feet) unbroken layer series of fossil sediments with bones from about 10 herbivorous dinosaurs that researchers found on expeditions in East Greenland.

Climate was a barrier

Using studies of these ancient sedimentary deposits to help them, researchers learned that the herbivorous dinosaurs reached East Greenland exactly 214 million years ago. Interestingly, their timing coincides with a major climatic shift that most probably helped them move along. The event? A drastic decrease in atmospheric CO2 levels 215 million years ago.

“We are able to see that during the period leading up to the dinosaurs’ migration, there was ten times as much CO2 in the atmosphere than there is today. This made it difficult for them to disperse from their original habitat in the southern hemisphere, as higher levels of CO2 produce more extreme climatic conditions,” says Lars Clemmensen, professor in the geosciences and natural resource management department at the University of Copenhagen.

“The desert areas they needed to traverse were excruciatingly hot and dry and the humid equatorial areas were tremendously unstable and wet. As such, climate was most likely a barrier that delayed the dinosaurs’ northbound dispersion,” Clemmensen says.

Researchers used magnetostratigraphic studies to perform the dating. They read the Earth’s ancient magnetic fields in ancient lake deposits and compare them to similar, well-dated sedimentary sea deposits from elsewhere in the world.

Even on a global scale, the researchers’ access to a 350-meter thick, unbroken, layered series of fossils, which includes early herbivorous dinosaurs and other contemporaneous vertebrates, is unique. The unbroken layers allowed them to accurately read changes in Earth’s ancient magnetic fields and made dating the layers safe.

Carnivorous dinosaurs were super speedy

Herbivorous dinosaurs weren’t alone in East Greenland, which at the time was at the same latitude as the northeastern United States. Therefore, the area had a humid temperate climate.

Small carnivorous dinosaurs had also made their way there. The fossil finds in East Greenland and elsewhere also demonstrate that carnivorous dinosaurs were better at overcoming extreme climate barriers and migrating to new lands compared to their herbivorous relatives. The researchers’ preliminary analyses show that the meat eaters reached East Greenland 600,000 years before herbivorous dinosaurs.

Clemmensen, along with Danish, European, and American researchers, has been on seven expeditions. Along the way, he has taken part in the work of discovering bones not only from herbivorous dinosaurs, but from carnivorous dinosaurs, flying lizards, labyrinthodontia, and early mammals. The new dating method makes it possible to precisely determine their ages.

“With this new and very precise chronology, we have a tool to better understand the dispersal pattern of many early vertebrates on Pangea. This holds especially true in the area between Northern Europe and East Greenland. We can go into every layer of soil where we have found bones and precisely determine their age,” Clemmensen says.