Related MediaFeb 17, 2021 13:45:45 IST
Plant-eating dinosaurs seem to have reached the Northern Hemisphere millions of years after their meat-eating cousins, a delay caused by climate change, a new study has found. A new method of dates dinosaur fossils found in Greenland shows that the eaters of the plants, known as sauropodomorphs, were about 215 million years old, according to a study on Monday. Proceedings of the National Academy of Sciences. The fossils were previously thought to be as old as 228 million years. That changes the way scientists think about dinosaur migration.
The earliest dinosaurs today appeared to have evolved in South America around 230 million years ago or more. They would then go north and across the globe. The new study suggests that dinosaurs could not migrate at the same time.
To date, scientists have not found any example of the earliest plant-eating dinosaur family in the Northern Hemisphere that is more than 215 million years old. One of the best examples of these is the Plateosaurus, a 23-foot (7-meter) two-legged vegetarian who weighed 8,800 pounds (4,000 kilograms). But scientists are discovering that meat eaters were largely worldwide at least 220 million years ago, said Randy Irmis, a paleontologist at the University of Utah, who was not part of the research.
Plant eaters were “latecomers in the Northern Hemisphere,” said study lead author Dennis Kent, of Columbia University. “What took so long?”
Plateosaurus Models at the State Museum of Natural History in Stuttgart, Germany. Image Credit: Randall Irmis / AP
Kent figured out what might have happened by looking at the atmosphere and climate at the time. During the Triassic, 230 million years ago, carbon dioxide levels were 10 times higher than they are now. It was a warmer world without ice shelves at the poles and two bands of extreme deserts north and south of the equator, he said.
It was so dry in those regions that there weren’t enough plants for the sauropodomorphs to survive the trip, but there were enough insects that meat eaters could eat, Kent said.
But then about 215 million years ago, carbon dioxide levels fell in half and that allowed the deserts to gain a little more plant life and the sauropodomorphs were able to make the journey.
Kent and other scientists said Triassic’s changes in carbon dioxide levels came from volcanoes and other natural forces – unlike right now, when burning coal, oil and natural gas are the main drivers.
Plateosaurus Models at the State Natural History Museum in Stuttgart. Plant-eating dinosaurs like the Northern Hemisphere appear to have reached millions of years later than their meat-eating cousins, according to a study published on February 16, 2021. Image: Randall Irmis / AP
Kent used changes in the Earth’s magnetism in the soil to mark the more accurate date of Greenland’s fossils. That highlighted the migration time gap, said several outside experts both in dinosaurs and and old-fashioned.
Kent’s theory of climate change as the difference in dinosaur migration is “very cool because it brings back contemporary issues,” Irmis said.
It also responds to some animals around today that have migratory issues that keep them away from a particular climate, said Hans-Otto Portner, climate scientist and biologist at the Alfred Wegener Institute in Germany that was not part of the study.
While the study makes sense, there is one potential flaw, said University of Chicago dinosaur expert Paul Sereno: Just because fossils of plant-eaters older than 215 million years old have not been found in the Northern Hemisphere, that does not mean that there were no sauropodomorphs. The fossils may not have survived, he said.