There is a much greater similarity between the flowering plant floras of different continents—South America, Africa, Asia, and Australia—than between the mammalian faunas (animals) of these regions. Only in the case of the African/Asian comparison are the plant and animal figures at a similar level. Three factors seem to have caused these differences.
First, the families of flowering plants evolved and dispersed earlier than the families of mammals. Recent palaeobotanical techniques have made it possible to retrieve and identify complete and partial flowers from sediments from the middle Cretaceous (144 to 65 million years ago). These demonstrate that several currently existing families had appeared by the middle Cretaceous, about 120 million years ago, and at least a dozen by 95 to 5 million years ago. Therefore, the angiosperms (flowering plants) commenced their dispersal across the world much earlier than the mammals, and thus had a much greater chance of reaching the different continents before they drifted far apart. In contrast, the diversification and dispersal of modern mammals only began in the earliest Cenozoic, 66 to 65 million years ago, by which time the continents had drifted farther apart and were more difficult to reach. However, those mammals that did succeed as colonists were able, in the isolation of each continent, to diverge into a number of unique, native groups that show little similarity to those in other continents, for example New World monkeys in South America, elephants and aardvarks in Africa, and marsupials like the kangaroo in Australia.
Secondly, there has been more extinction and replacement during the history of mammals than during that of flowering plants. For example, in addition to the approximately 100 living families of mammals, over 300 other families evolved and became extinct during the Cenozoic—some 70 percent of the families of mammals died out completely. Some of these were previously widespread families, which were replaced in the now-separate continents by new families found only in those particular regions. In other cases, the family became extinct only in some areas, so that it now had a disjunct distribution, with widely separated subgroups, as in the camel-llama group. Another example of the influence of extinction is seen if one compares the similarities between the mammal faunas of North and South America before and after a wave of extinctions in the Pleistocene (1.8 million to 10,000 years ago). All these phenomena reduced the levels of similarity between the faunal regions. In the flowering plants, in contrast, there has been much less extinction. Furthermore, groups of plants are much longer-lived than are those of mammals. For example, the distribution of the southern beech tree, Nothofagus, shows that it evolved in the Late Cretaceous, at least 70 million years ago, while the average longevity of mammalian groups is only eight million years.
Finally, of course, not all floral similarities were merely the result of early dispersal across insignificant barriers rather than a later colonization across wider gaps. The extent of the spread of flowering plants across the Pacific (over 200 different immigrant flowering plants have reached the most isolated island group, Hawaii) shows clearly that they can cross even quite wide stretches of ocean, especially where intermediate island steppingstones were available.
For all these reasons, it is not surprising that the flora of the different continents shows more similarities to one another than do their mammalian faunas. However, there is one exception: the almost identical levels of similarity for the two groups when the African and Asian regions are compared. The floral similarity here is not surprising, for it is at the same general level as the similarities between the other tropical regions. It is therefore the faunal similarity between the African and Asian regions that is unexpectedly high. This is probably because of the faunal exchange that took place between Africa and Eurasia after the two continents became connected in the Miocene era (28.3 to 5.3 million years ago) and before deserts spread through the Middle East.
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First, the families of flowering plants evolved and dispersed earlier than the families of mammals. Recent palaeobotanical techniques have made it possible to retrieve and identify complete and partial flowers from sediments from the middle Cretaceous (144 to 65 million years ago). These demonstrate that several currently existing families had appeared by the middle Cretaceous, about 120 million years ago, and at least a dozen by 95 to 5 million years ago. Therefore, the angiosperms (flowering plants) commenced their dispersal across the world much earlier than the mammals, and thus had a much greater chance of reaching the different continents before they drifted far apart. In contrast, the diversification and dispersal of modern mammals only began in the earliest Cenozoic, 66 to 65 million years ago, by which time the continents had drifted farther apart and were more difficult to reach. However, those mammals that did succeed as colonists were able, in the isolation of each continent, to diverge into a number of unique, native groups that show little similarity to those in other continents, for example New World monkeys in South America, elephants and aardvarks in Africa, and marsupials like the kangaroo in Australia.
The word “demonstrate” in the passage is closest in meaning to
Aargue
Bshow
Cemphasize
Dconclude
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First, the families of flowering plants evolved and dispersed earlier than the families of mammals. Recent palaeobotanical techniques have made it possible to retrieve and identify complete and partial flowers from sediments from the middle Cretaceous (144 to 65 million years ago). These demonstrate that several currently existing families had appeared by the middle Cretaceous, about 120 million years ago, and at least a dozen by 95 to 5 million years ago. Therefore, the angiosperms (flowering plants) commenced their dispersal across the world much earlier than the mammals, and thus had a much greater chance of reaching the different continents before they drifted far apart. In contrast, the diversification and dispersal of modern mammals only began in the earliest Cenozoic, 66 to 65 million years ago, by which time the continents had drifted farther apart and were more difficult to reach. However, those mammals that did succeed as colonists were able, in the isolation of each continent, to diverge into a number of unique, native groups that show little similarity to those in other continents, for example New World monkeys in South America, elephants and aardvarks in Africa, and marsupials like the kangaroo in Australia.
According to paragraph 2, how do we know that flowering plants had appeared before the continents drifted far apart?
AFrom the large number of living flowering plants that can be traced back to the Cenozoic
BFrom flowers found in sediments dating to the middle Cretaceous
CFrom the fact that the earliest flowering plants were not very successful at colonizing across oceans
DFrom the fact that flowering plants reached all the continents before mammals did
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First, the families of flowering plants evolved and dispersed earlier than the families of mammals. Recent palaeobotanical techniques have made it possible to retrieve and identify complete and partial flowers from sediments from the middle Cretaceous (144 to 65 million years ago). These demonstrate that several currently existing families had appeared by the middle Cretaceous, about 120 million years ago, and at least a dozen by 95 to 5 million years ago. Therefore, the angiosperms (flowering plants) commenced their dispersal across the world much earlier than the mammals, and thus had a much greater chance of reaching the different continents before they drifted far apart. In contrast, the diversification and dispersal of modern mammals only began in the earliest Cenozoic, 66 to 65 million years ago, by which time the continents had drifted farther apart and were more difficult to reach. However, those mammals that did succeed as colonists were able, in the isolation of each continent, to diverge into a number of unique, native groups that show little similarity to those in other continents, for example New World monkeys in South America, elephants and aardvarks in Africa, and marsupials like the kangaroo in Australia.
The author mentions “New World monkeys in South America” in order to
Agive an example of the range of mammals that are now found only in isolated regions within continents
Bsupport the point that mammals generally dispersed later than flowering plants did
Cexplain how groups of mammals were able to succeed as colonists on different continents as a result of diversification
Dgive an example of a group of mammals that developed in isolation and are now very different from their closest relatives on other continents
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Secondly, there has been more extinction and replacement during the history of mammals than during that of flowering plants. For example, in addition to the approximately 100 living families of mammals, over 300 other families evolved and became extinct during the Cenozoic—some 70 percent of the families of mammals died out completely. Some of these were previously widespread families, which were replaced in the now-separate continents by new families found only in those particular regions. In other cases, the family became extinct only in some areas, so that it now had a disjunct distribution, with widely separated subgroups, as in the camel-llama group. Another example of the influence of extinction is seen if one compares the similarities between the mammal faunas of North and South America before and after a wave of extinctions in the Pleistocene (1.8 million to 10,000 years ago). All these phenomena reduced the levels of similarity between the faunal regions. In the flowering plants, in contrast, there has been much less extinction. Furthermore, groups of plants are much longer-lived than are those of mammals. For example, the distribution of the southern beech tree, Nothofagus, shows that it evolved in the Late Cretaceous, at least 70 million years ago, while the average longevity of mammalian groups is only eight million years.
The word “Furthermore” in the passage is closest in meaning to
AHowever
BTherefore
CIn addition
DIn effect
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Secondly, there has been more extinction and replacement during the history of mammals than during that of flowering plants. For example, in addition to the approximately 100 living families of mammals, over 300 other families evolved and became extinct during the Cenozoic—some 70 percent of the families of mammals died out completely. Some of these were previously widespread families, which were replaced in the now-separate continents by new families found only in those particular regions. In other cases, the family became extinct only in some areas, so that it now had a disjunct distribution, with widely separated subgroups, as in the camel-llama group. Another example of the influence of extinction is seen if one compares the similarities between the mammal faunas of North and South America before and after a wave of extinctions in the Pleistocene (1.8 million to 10,000 years ago). All these phenomena reduced the levels of similarity between the faunal regions. In the flowering plants, in contrast, there has been much less extinction. Furthermore, groups of plants are much longer-lived than are those of mammals. For example, the distribution of the southern beech tree, Nothofagus, shows that it evolved in the Late Cretaceous, at least 70 million years ago, while the average longevity of mammalian groups is only eight million years.
According to paragraph 3, which of the following is true of mammals?
AAll of the currently living families had evolved by the beginning of the Cenozoic.
BThe families that still exist consist of widely separated subgroups.
CThe majority of families became extinct during the Cenozoic.
DThe families that became extinct during the Cenozoic were more widespread than those that survived.
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Secondly, there has been more extinction and replacement during the history of mammals than during that of flowering plants. For example, in addition to the approximately 100 living families of mammals, over 300 other families evolved and became extinct during the Cenozoic—some 70 percent of the families of mammals died out completely. Some of these were previously widespread families, which were replaced in the now-separate continents by new families found only in those particular regions. In other cases, the family became extinct only in some areas, so that it now had a disjunct distribution, with widely separated subgroups, as in the camel-llama group. Another example of the influence of extinction is seen if one compares the similarities between the mammal faunas of North and South America before and after a wave of extinctions in the Pleistocene (1.8 million to 10,000 years ago). All these phenomena reduced the levels of similarity between the faunal regions. In the flowering plants, in contrast, there has been much less extinction. Furthermore, groups of plants are much longer-lived than are those of mammals. For example, the distribution of the southern beech tree, Nothofagus, shows that it evolved in the Late Cretaceous, at least 70 million years ago, while the average longevity of mammalian groups is only eight million years.
According to paragraph 3, the similarity between the mammals of North America and those of South America was significantly reduced by
Athe large number of mammal families that went extinct in the Pleistocene
Bthe spread of certain families of mammals at the expense of others
Cdifferences in how rapidly different families of mammals dispersed through the continents
Ddifferences in the number of subgroups that developed on each continent
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Finally, of course, not all floral similarities were merely the result of early dispersal across insignificant barriers rather than a later colonization across wider gaps. The extent of the spread of flowering plants across the Pacific (over 200 different immigrant flowering plants have reached the most isolated island group, Hawaii) shows clearly that they can cross even quite wide stretches of ocean, especially where intermediate island steppingstones were available.
The discussion of “Hawaii” supports the idea that families of plants would probably be more widespread than families of mammals even if
Athere had not been significant barriers to the dispersal of mammals
Bmany families of plants had gone extinct in some areas but not in others
Cplants had not dispersed before the continents drifted apart
Dthere had been more extinction among plants than among mammals
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For all these reasons, it is not surprising that the flora of the different continents shows more similarities to one another than do their mammalian faunas. However, there is one exception: the almost identical levels of similarity for the two groups when the African and Asian regions are compared. The floral similarity here is not surprising, for it is at the same general level as the similarities between the other tropical regions. It is therefore the faunal similarity between the African and Asian regions that is unexpectedly high. This is probably because of the faunal exchange that took place between Africa and Eurasia after the two continents became connected in the Miocene era (28.3 to 5.3 million years ago) and before deserts spread through the Middle East.
According to paragraph 5, what probably explains the high animal similarity between the African and Asian regions?
AThe animal exchange between the two regions occurred earlier than exchanges between other regions.
BFor a period after Africa and Eurasia connected, animals could cross from one region to the other relatively easily.
CThe flora of the two regions were highly similar before the continents became connected.
DMammals were able to adapt to the deserts that eventually spread throughout most of the Middle East.
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Secondly, there has been more extinction and replacement during the history of mammals than during that of flowering plants. For example, in addition to the approximately 100 living families of mammals, over 300 other families evolved and became extinct during the Cenozoic—some 70 percent of the families of mammals died out completely. Some of these were previously widespread families, which were replaced in the now-separate continents by new families found only in those particular regions. In other cases, the family became extinct only in some areas, so that it now had a disjunct distribution, with widely separated subgroups, as in the camel-llama group. Another example of the influence of extinction is seen if one compares the similarities between the mammal faunas of North and South America before and after a wave of extinctions in the Pleistocene (1.8 million to 10,000 years ago). [■] All these phenomena reduced the levels of similarity between the faunal regions.[■] In the flowering plants, in contrast, there has been much less extinction. [■] Furthermore, groups of plants are much longer-lived than are those of mammals. [■] For example, the distribution of the southern beech tree, Nothofagus, shows that it evolved in the Late Cretaceous, at least 70 million years ago, while the average longevity of mammalian groups is only eight million years.
Look at the four squaresthat indicate where the following sentence could be added to the passage
In fact, there is no record yet of the extinction of a major group of flowering plants.
Where would the sentence best fit？Click on a square sentence to the passage.
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Mammals on different continents are more different from each other than are flowering plants on the same continents.
AUnlike mammals, flowering plants appeared and spread before the continents drifted apart, which helps explain the greater similarity of flora than of fauna between continents.
BBy reconstructing complete flowers from flower parts found in ancient sediments, scientists have shown that most currently existing families had not yet appeared by the middle Cretaceous.
CResearch on the separation of continents and dispersal of species has shown that the oldest living groups of plants were first found in South America.
DUnlike plants, many families of mammals died out and were replaced by families unique to certain regions, or else evolved very differently on different continents.
EThe floral similarity between isolated islands such as Hawaii and other tropical regions is not as great as that between continents that were connected when flowering plants first appeared.
FPlants can spread across wide stretches of ocean, but mammals generally can spread only when there is a land connection—such as that which appeared between Africa and Eurasia in the Miocene.
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