1. At the end of the Pleistocene (roughly 11,500 years ago), many large mammals became extinct. Large mammals in the Americas and Australia were particularly hard-hit. In Australia, 15 of the continent's 16 of large mammals died out; North America lost 33 of 45 genera of large mammals, and in South America 46 of 58 such genera went extinct. In contrast, Europe lost only 7 of 23 such genera, and in Africa south of the Sahara only 2 of 44 died out. What caused these extinctions Why did these extinctions eliminate mostly large mammals Why were the extinctions most severe in Australia and the Americas No completely satisfactory explanation exists, but two competing hypotheses are currently being debated. One holds that rapid climatic changes at the end of the Pleistocene caused extinctions, whereas another, called prehistoric overkill, holds that human hunters were responsible.
2. Rapid changes in climate and vegetation occurred over much of Earth's surface during the late Pleistocene, as glaciers began retreating. The North American and northern Eurasian open steppe tundras (treeless and permanently frozen land areas) were replaced by conifer and broadleaf forests as warmer and wetter conditions prevailed. The Arctic region changed from a productive herbaceous one that supported a variety of large mammals, to a relatively barren waterlogged tundra that supported a far sparser fauna. The southwestern United States region also changed from a moist area with numerous lakes, where saber-tooth cats, giant ground sloths, and mammoths roamed, to a semiarid environment unable to support a diverse fauna of large mammals.
3. Rapid changes in climate and vegetation can certainly affect animal populations, but the climate hypothesis presents several problems. First, why did the large mammals not migrate to more suitable habitats as the climate and vegetation changed After all, many other animal species did. For example, reindeer and the arctic fox lived in southern France during the last glaciation and migrated to the Arctic when the climate became warmer.
4. The second argument against the climatic hypothesis is the apparent lack of correlation between extinctions and the earlier glacial advances and retreats throughout the Pleistocene Epoch. Previous changes in climate were not marked by episodes of mass extinctions.
5. Proponents of the prehistoric overkill hypothesis argue that the mass extinctions in North and South America and Australia coincided closely with the arrival of humans. Perhaps hunters had a tremendous impact on the faunas of North and South America about 11,000 years ago because the animals had no previous experience with humans. The same thing happened much earlier in Australia soon after people arrived about 40,000 years ago. No large-scale extinctions occurred in Africa and most of Europe because animals in those regions had long been familiar with humans.
6. One problem with the prehistoric overkill hypothesis is that archaeological evidence indicates the early human inhabitants of North and South America, as well as Australia, probably lived in small, scattered communities, gathering food and hunting. How could a few hunters destroy so many species of large mammals However, it is true that humans have caused major extinctions on oceanic islands. For example, in a period of about 600 years after arriving in New Zealand, humans exterminated several species of the large, flightless birds called moas. A second problem is that present-day hunters concentrate on smaller, abundant, and less dangerous animals. The remains of horses, reindeer, and other small animals are found in many prehistoric sites in Europe, whereas mammoth and woolly rhinoceros remains are scarce. Finally, few human artifacts are found among the remains of extinct animals in North and South America, and there is usually little evidence that the animals were hunted. Countering this argument is the assertion that the impact on the previously unhunted fauna was so swift as to leave little evidence.
7. The reason for the extinctions of large Pleistocene mammals is still unresolved and probably will be for some time. It may turn out that the extinctions resulted from a combination of different circumstances. Populations that were already under stress from climate changes were perhaps more vulnerable to hunting, especially if smaller females and young animals were the preferred targets.
1..According to paragraph 1, which of the following groups of mammals experienced a high extinction rate at the end of the Pleistocene
A. Large mammals living in North America
B. Small mammals living in South America
C. Large mammals living in South Africa
D. Large mammals living in Europe
2..According to paragraph 1, researchers have been able to answer which of the following questions about late Pleistocene extinctions
A. Why did some parts of the world experience more extinctions than others
B. Which parts of the world experienced the greatest number of extinctions
C. Did the large mammals of the Americas or Australia become extinct first
D. How rapidly did the climate change during the extinctions
3..What can be inferred from paragraph 1 about the extinctions that occurred at the end of the Pleistocene
A. They were caused by a single factor.
B. They had relatively little impact on small mammals.
C. They wiped out nearly all of the world's large mammal species.
D. They occurred slowly over a period of thousands of years.
4..The word sparser in the passage is closest in meaning to
A. more thinly distributed
B. more threatened
C. less adapted
D. less mobile
5..All of the following are mentioned in paragraph 2 as changes that occurred during the late Pleistocene EXCEPT:
A. The Eurasian tundras became more forested as both temperature and rainfall increased.
B. The Arctic region became less productive, and much of its fauna and flora began to disappear.
C. The southwestern United States became much drier, resulting in a decline in species diversity.
D. The North American open steppe tundras became cooler, resulting in a decrease in vegetation.
6..In paragraph 3, why does the author point out that some animals living in southern France migrated to the Arctic when the climate became warmer
A. To show that more suitable habitats existed at the time that the megafauna became extinct
B. To question the idea that the megafauna were able to migrate to more suitable habitats
C. To provide evidence that weakens the climate hypothesis for the megafauna extinctions
D. To argue that smaller animals are more successful at adapting to rapid changes in climate
7..The word episodes in the passage is closest in meaning to
8..The word Proponents in the passage is closest in meaning to
9..In paragraph 5, why does the author discuss what happened in Australia 40,000 years ago
A. To suggest that humans most likely arrived in North and South America much earlier than 11,000 years ago
B. To make a comparison that supports the prehistoric overkill hypothesis
C. To argue that most extinctions can be traced to the impact of humans on the environment
D. To emphasize the similarities between the extinctions that occurred in Australia and those that occurred in Africa and Europe
10..The word swift in the passage is closest in meaning to
11..According to paragraph 6, archaeological evidence of settlement patterns in North and South America indicates which of the following
A. Human populations may have been too small and too far apart to have caused the extinction of large mammals.
B. Humans may have lived too far away from the habitats of large mammals to have been responsible for their extinctions.
C. Humans probably did not cause the extinction of large mammals, because they spent far more time gathering food than hunting.
D. Humans probably did not remain in their settlements long enough to have a significant impact on populations of large mammals.
12..In paragraph 6, the author identifies all of the following as being problems with the prehistoric overkill hypothesis EXCEPT:
A. There were not enough people to kill so many species of large animals.
B. There is little evidence to show that extinct animals were hunted.
C. Prehistoric Europeans apparently preferred hunting smaller animals.
D. It took 600 years for humans in New Zealand to exterminate just a few species of moa birds.
13.. Look at the four squares that indicate where the following sentence could be added to the passage.
It should be noted, however, that island conditions that lead to extinction, such as limited space to escape predators, do not apply to landmasses such as continents.
Where would the sentence best fit Click on a square to add the sentence to the passage.
14..Drag your choices to the spaces where they belong. To review the passage, click on View
A. Rapid climate change has been proposed as a cause of the extinctions, though there is strong evidence that mammals were able to survive similar climate changes in the past.
B. The climatic hypothesis has gained more support than the prehistoric overkill hypothesis because climate change can explain why very few extinctions occurred in Europe and Africa.
C. Some researchers have begun to doubt the idea that mass extinctions occurred at the end of the Pleistocene, because large animal remains are rarely found at settlements dating from this time.
D. Late Pleistocene hunters may have killed off large mammals when they first arrived in certain areas, but evidence from settlements and animal remains does not often support this hypothesis.
E. According to the prehistoric overkill hypothesis, the extinctions were concentrated in North and South America because these areas had more hunters and smaller populations of large mammals.
F. Although neither the climatic hypothesis nor the prehistoric overkill hypothesis alone explains late Pleistocene extinctions, elements of both and other factors may have contributed to the extinctions.