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Herbivorous dinosaurs likely arrived in the northern hemisphere millions of years after their carnivorous cousins, a delay likely caused by climate change, according to a new study.
A new way to calculate the dates of dinosaur fossils found in Greenland showed that plant eaters, called sauropodomorphs, were around 215 million years old, instead of 228 million years old as previously thought, study finds published Monday in Proceedings of the National. Academy of Sciences.
It changes the way scientists think about dinosaur migration.
The earliest dinosaurs all seemed to first develop in what is now South America around 230 million years or more ago. They then wandered north and all over the world. The new study suggests that not all dinosaurs could migrate at the same time.
So far, scientists have not found any examples of the northern hemisphere’s oldest family of herbivorous dinosaurs, which is over 215 million years old. One of the best examples of these is the Plateosaurus, a two-legged 7-meter vegetarian who weighed 8,800 lbs (4,000 kg).
Still, scientists find meat eaters were roughly in the world at least 220 million years ago, said Randy Irmis, a paleontologist at the University of Utah, who was not part of the research.
The plant eaters “were late arrivals to the northern hemisphere,” said lead author Dennis Kent of Columbia University. “What took them so long?”
Kent understood what probably happened by looking at the atmosphere and climate at the time. During the Triassic era, 230 million years ago, carbon dioxide levels were 10 times higher than today. It was a warmer world with no ice caps at the poles and with two bands of extreme deserts north and south of the equator, he said.
It was so dry in those areas that there weren’t enough plants for the sauropodomorphs to survive the trip, but there were enough insects that the meat-eaters could, Kent said.
But about 215 million years ago, carbon dioxide levels briefly halved and that allowed deserts to have a few more plants and sauropodomorphs to make the trip.
Kent and other scientists said the Triassic changes in carbon dioxide levels were due to volcanoes and other natural forces – unlike now, when the burning of coal, oil, and natural gas are the primary drivers. .
Kent used changes in the Earth’s magnetism in the soil to identify the more exact date of the Greenland fossils. This highlighted the migration time lag, several outside dinosaur and ancient climate experts said.
Kent’s theory that climate change is the difference in dinosaur migration “is super cool because it brings it back to contemporary issues,” Irmis said.
It also fits with some animals today that have migration issues that keep them away from certain climates, said Hans-Otto Pörtner, climatologist and biologist at the Alfred Wegener Institute in Germany who was not part of the study.
While the study makes sense, there is a potential flaw, said University of Chicago dinosaur expert Paul Sereno: Just because no plant-eating fossils over 215 million years ago has not been found in the northern hemisphere, this does not mean that there have not been sauropodomorphs. The fossils may not have survived, he said.
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