Study: Plant-eating Dinosaurs Arrived Late to Northern Half of the World
2021-02-21
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1Plant-eating dinosaurs probably arrived in the northern half of the world millions of years after meat-eating dinosaurs, a recent study found.
2Their late arrival was likely a result of climate changes that took place hundreds of millions of years ago.
3The study used a new way to estimate the age of dinosaur remains found in Greenland.
4Researchers found that the plant-eating dinosaurs were about 215 million years old.
5The mineralized remains of bones are called fossils.
6Earlier, those fossils were thought to be as old as 228 million years.
7The findings appeared in Proceedings of the National Academy of Sciences of the United States of America.
8They could change how scientists think about dinosaur movements, or migrations.
9The earliest dinosaurs all seemed to first develop about 230 million years ago or longer.
10They appeared in what is now South America.
11Then, the creatures moved north and spread all over the world.
12The new study suggests not all dinosaurs moved at the same time.
13So far, scientists have not found any evidence of plant-eating dinosaurs living in the Northern Hemisphere before 215 million years ago.
14One of the best examples of these is the Plateosaurus, a two-legged, 7-meter-long plant-eater that weighed around 4,000 kilograms.
15However, meat-eaters lived worldwide by at least 220 million years ago, said Randy Irmis of the University of Utah.
16Irmis was not part of the research.
17Dennis Kent of Columbia University was the lead writer of the study.
18The plant-eaters "were late comers in the Northern Hemisphere," he said.
19Then he asked, "What took them so long?"
20By studying the atmosphere and the climate of the time period, Kent believes he has found an answer.
21During the Triassic period, 230 million years ago, carbon dioxide levels were 10 times higher than now.
22The Earth was hotter with no ice sheets at the poles and two areas of extreme deserts north and south of the equator, he said.
23It was so dry in those areas that there were not enough plants for the plant-eaters to survive.
24But there were enough insects so that meat-eaters could, Kent said.
25About 215 million years ago, carbon dioxide levels dropped.
26The drop resulted in more plant life in the deserts.
27The plant-eaters were then able to make the trip.
28Kent and other scientists said Triassic changes in carbon dioxide levels were from volcanoes and other natural forces.
29The changes were different from our time, when the burning of coal, oil and natural gas are considered the main causes of climate change.
30Kent used changes in Earth's magnetism to find the age of fossils in Greenland.
31Several outside experts both in dinosaurs and ancient climate said this shows that there was a time difference between the migrations of the two kinds of dinosaurs.
32Irmis described Kent's theory about how ancient climate affected dinosaurs as "super cool because it brings it back to contemporary issues."
33Contemporary is a term that means happening or beginning in recent times.
34Hans-Otto Portner of the Alfred Wegener Institute in Germany also was not part of the study.
35Portner suggested that the study's findings fit with some animals behaviors today.
36Paul Sereno of the University of Chicago said that the study makes sense.
37But, he added, it does have one possible weakness.
38Just because researchers have not found evidence of fossils older than 215 million years does not mean there were no plant-eaters in the Northern Hemisphere.
39The fossils just may not have survived, he noted.
40I'm John Russell.
1Plant-eating dinosaurs probably arrived in the northern half of the world millions of years after meat-eating dinosaurs, a recent study found. Their late arrival was likely a result of climate changes that took place hundreds of millions of years ago. 2The study used a new way to estimate the age of dinosaur remains found in Greenland. Researchers found that the plant-eating dinosaurs were about 215 million years old. The mineralized remains of bones are called fossils. Earlier, those fossils were thought to be as old as 228 million years. 3The findings appeared in Proceedings of the National Academy of Sciences of the United States of America. They could change how scientists think about dinosaur movements, or migrations. 4The earliest dinosaurs all seemed to first develop about 230 million years ago or longer. They appeared in what is now South America. Then, the creatures moved north and spread all over the world. The new study suggests not all dinosaurs moved at the same time. 5So far, scientists have not found any evidence of plant-eating dinosaurs living in the Northern Hemisphere before 215 million years ago. One of the best examples of these is the Plateosaurus, a two-legged, 7-meter-long plant-eater that weighed around 4,000 kilograms. 6However, meat-eaters lived worldwide by at least 220 million years ago, said Randy Irmis of the University of Utah. Irmis was not part of the research. 7Dennis Kent of Columbia University was the lead writer of the study. The plant-eaters "were late comers in the Northern Hemisphere," he said. Then he asked, "What took them so long?" 8By studying the atmosphere and the climate of the time period, Kent believes he has found an answer. During the Triassic period, 230 million years ago, carbon dioxide levels were 10 times higher than now. The Earth was hotter with no ice sheets at the poles and two areas of extreme deserts north and south of the equator, he said. 9It was so dry in those areas that there were not enough plants for the plant-eaters to survive. But there were enough insects so that meat-eaters could, Kent said. 10About 215 million years ago, carbon dioxide levels dropped. The drop resulted in more plant life in the deserts. The plant-eaters were then able to make the trip. Kent and other scientists said Triassic changes in carbon dioxide levels were from volcanoes and other natural forces. The changes were different from our time, when the burning of coal, oil and natural gas are considered the main causes of climate change. 11Kent used changes in Earth's magnetism to find the age of fossils in Greenland. Several outside experts both in dinosaurs and ancient climate said this shows that there was a time difference between the migrations of the two kinds of dinosaurs. 12Irmis described Kent's theory about how ancient climate affected dinosaurs as "super cool because it brings it back to contemporary issues." Contemporary is a term that means happening or beginning in recent times. 13Hans-Otto Portner of the Alfred Wegener Institute in Germany also was not part of the study. Portner suggested that the study's findings fit with some animals behaviors today. 14Paul Sereno of the University of Chicago said that the study makes sense. But, he added, it does have one possible weakness. 15Just because researchers have not found evidence of fossils older than 215 million years does not mean there were no plant-eaters in the Northern Hemisphere. The fossils just may not have survived, he noted. 16I'm John Russell. 17Seth Borenstein reported on this story for the Associated Press. John Russell adapted it for Learning English. Mario Ritter, Jr. was the editor. 18____________________________________________________________ 19Words in This Story 20hemisphere -- n. a half of the Earth 21sheet -- n. a wide, flat surface or area of something 22pole - n. either end of the imaginary line around which something (such as the earth) turns 23magnetism -n. the property of attracting certain metals : the attracting property of a magnet 24cool -adj. appealing, approved of