In the Late Triassic period about 252 million years ago, the planet was mostly a vast arid desert assembled into the supercontinent Pangea. Meat-eating dinosaurs roamed the planet with ease, expanding their range throughout the land. But herbivores, whose diet is dependent on an abundance of plants, were geographically confined to greener areas, including the largest dinosaurs—and land animals—that ever lived: a group of massive, long-necked dinos called sauropodomorphs.
For millions of years, sauropodomorphs didn't really budge from their habitats in what is today Argentina and Brazil—until a dip in carbon dioxide (CO2) levels occurred 215 million years ago, reports Chrissy Sexton for Earth.com. The shift in CO2 levels may have made it easier for a group of herbivores called sauropodomorphs to migrate North, according to a new study in the journal Proceedings of the National Academy of Sciences.
"In principle, the dinosaurs could have walked from almost one pole to the other. 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,” says Dennis Kent, study co-author and geologist at Columbia University, in a statement.
It was previously thought that sauropodomorphs migrated to Greenland around 205 million to 225 million years ago. By measuring magnetism patterns within ancient rocks from South America, Arizona, New Jersey, Europe and Greenland, the authors of the new study found that the herbivores actually migrated closer to 214 million years ago, a time where Earth’s climate was rapidly changing, reports Anushree Dave for Science News.
During the late Triassic period between 215 million to 233 million years ago, Earth had extremely high carbon dioxide levels at 4,000 parts per million, Science News reports. The high CO2 levels would have made dry environments extremely arid and wet environments monsoonal, limiting the amount of plants the herbivores could feast on while migrating, reports Harry Cockburn for the Independent.
Between 212 million and 215 million years ago when the sauropodomorphs arrived in Greenland, carbon dioxide levels were halved at 2,000 parts per million, leaving researchers to suspect that this event may have made conditions on Earth more hospitable. Tropical regions likely became more mild and arid regions became less dry, allowing sauropodomorphs to migrate North, reports the Independent.
Researchers have found an abundance of sauropod fossils in what is now Greenland, suggesting that the climate and environment was suitable for the dinosaurs and they decided to stick around.
“Once they arrived in Greenland, it looked like they settled in. They hung around as a long fossil record after that,” Kent tells the Independent. Fossilized footprints of these long-necked dinosaurs are found in tropical and arid regions, but their bodies are not, suggesting they were only passing through while on their journey to Greenland, reports the Independent.
“This study reminds us that we can’t understand evolution without understanding climate and environment," says Steve Brusatte, a vertebrate paleontologist at the University of Edinburgh, who was not involved with the study, to Science News. "Even the biggest and most awesome creatures that ever lived were still kept in check by the whims of climate change."