Climate change 'delayed migration of big plant-eating dinosaurs by millions of years'
New study of fossils suggests arrival in northern hemisphere long after meat-eating cousins Large plant-eating dinosaurs probably arrived in the northern hemisphere millions of years after their meat-eating cousins, a delay probably caused by climate change , a new study has found. A new way of calculating the dates of dinosaur fossils found in Greenland showed that these plant eaters, big bipedal sauropodomorphs, were about 215m years old, instead of as much as 228m years old as previously thought, according to a study in Mondays Proceedings of the National Academy of Sciences. That changes how scientists think about dinosaur migration. The earliest dinosaurs all seemed to develop first in whats now South America about 230m years ago or longer. They then wandered north and all over the globe. The new study suggests not all dinosaurs could migrate at the same time. So far, scientists havent found any example of the earliest plant-eating dinosaur family in the northern hemisphere thats more than 215m years old. One of the best examples of these is the Plateosaurus, a two-legged 23ft (7-metre) vegetarian that weighed 8,800lb (4,000kg). It was on the first fossil appearances in Greenland of Plateosaurus that the new study focussed. Yet scientists find meat-eaters were pretty much worldwide by at least 220m years ago, said Randy Irmis, a paleontologist at the University of Utah, who wasnt part of the research. The plant eaters were late comers in the northern hemisphere, said study lead author Dennis Kent of Columbia University. What took them so long? Kent figured out what probably happened by looking at the atmosphere and climate at the time. During the Triassic era 230m years ago, carbon dioxide levels were 10 times higher than now. It was a hotter world with no ice sheets 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 were not enough plants for the sauropodomorphs to survive the journey, but there were enough insects that meat-eaters could, Kent said. But then about 215m years ago, carbon dioxide levels briefly halved and that allowed the deserts to have a bit more plant life and the sauropodomorphs to make the trip. Kent and other scientists said Triassic changes in carbon dioxide levels were from volcanoes and other natural forces unlike now, when the burning of coal, oil and natural gas are the main drivers. Kent used changes in the Earths magnetism in the soil to pinpoint the more exact date of the Greenland fossils. That highlighted the migration time gap, said several outside experts in dinosaurs and the ancient climate. Kents theory about climatic change being the difference in dinosaur migration is super cool because it brings it back to contemporary issues, said Irmis. It also fits with some animals around today that have migratory issues that keep them away from certain climates, said Hans-Otto Portner, a climate scientist and biologist at the Alfred Wegener Institute in Germany who wasnt part of the study. While the study makes sense, there is one potential flaw, said the University of Chicago dinosaur expert Paul Sereno: just because no fossils of plant-eaters older than 215m years have been found in the northern hemisphere, that doesnt mean there were no sauropodomorphs. The fossils just may not have survived, he said. This article was amended on 19 February 2021 to clarify that the studys focus was large sauropodomorphs, as distinct from all plant-eating dinosaurs.