All North American mammals except the opossum are placentals, which means that the female nourishes he run developed young through the placental membrane in the uterus.Marsupials such as the opossum have a different reproductive system and strategy. Most female marsupials have a pouch, a fold of skin over the teats, where the immature marsupials feed and undergo much of their development Marsupials differ from placentals in many other aspects of their body plan.These differences arose early in mammalian history, as far back as 75 to100 million years ago during the Cretaceous period. Marsupials are called “primitive” not only because of their ancient origin but also because their skeletal system is closer o that of the reptiles from which mammals evolved and because they appear to have been out competed and replaced by their placental competitors in many parts of the world. Among the primitive features that marsupials exhibit are a narrow brain case, a small brain, and more teeth. The common opossum, for example, has 50 teeth, whereas many placentals have only 44. The bones in a marsupial’s inner ear are not the same as those in a placental’s. But it is the evolutionary history of marsupials more than anything else that suggests they are less advanced than placental mammals.
1.According to paragraph 1, marsupials are considered primitive for all of the following reasons EXCEPT:
A.Their skeletal system is more similar to that of reptiles than to that of placental mammals.
B.They have a smaller number of teeth than do many placental animals.
C.They have been replaced by placental competitors in some habitats.
D.Their origin is ancient.
At the time the earliest marsupials began evolving, the three southern continents_Australia, Africa, and South America-were still joined in one large landmass. ▉When this landmass began breaking apart, Australia and South America became isolated from the other continents.▉In North America, Asia, Africa, and Europe,the placental mammals began to diversify and increase. Where as marsupials declined until, by 15 to 25 million years ago, they were surviving only in Australia and South America. ▉In Australia, where there was no competition from placental mammals, the marsupials diversified into a great variety of life forms, such as the large grazing kangaroos, the digging rodent-like wombats, koala bears.marsupial lions, and other carnivores such as the Tasmanian devil.▉
2.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.The increasing variety of placental mammals in Africa and the northern continents failed to reduce the number of marsupial mammals that survived, except in Australia and South America
B.Changes in the populations of mammals around 15 to 25 million years ago left fewer varieties of marsupials surviving on all continents except South America and Australia.
C.By 15 to 25 million years ago, a variety of marsupials remained in Australia and South America despite the increased difficulties that they faced there.
D.While placental mammals increased in variety and number,marsupials began to disappear so that by 15 to 25 million years ago, they existed only in Australia and South America.
3.In paragraph 2, why does the author mention various Australian marsupials?
A.To give examples of the large variety of marsupials that evolved in Australia
B.To explain why these animals are found primarily in Australia
C.To argue that Australian marsupials were more advanced than marsupials elsewhere
D.To provide evidence that by 15 to 25 million years ago.marsupials were surviving only in Australia and South America
The reconnection of South America and North America suggests that competitive extinctions were important in the decline of many marsupial groups. For some 60 million years, South America was separated from North America. During that interval, the South American marsupials diversified into forms that resembled giant hyenas and saber-toothed tigers. But when the land bridge linking the Americas arose some 2 to 5 million years ago, large placental carnivores such as jaguars and pumas began invading South America, an event shown by the fossil record to correspond with the extinction of their marsupial counterparts.
4.The word “resembled” in the passage is closest in meaning to
A.were similar to
B.developed into
C.competed with
D.lived together with
5.Paragraph 3 implies that in the years immediately before the formation of the land bridge linking the Americas, North America was home to
A.the same types of jaguars and pumas that were living in South America
B.marsupials that resembled giant hyenas and saber-toothed tigers
C.marsupial counterparts of South American jaguars and pumas
D.large, meat-eating placental mammals
However, not all marsupials have managed to survive simply because of a lack of competition with placental mammals, nor are all marsupials simply “living fossils,” animals that have not evolved significantly over time. In spite of a long history of contact with placental mammals, marsupial opossums have survived, and indeed, have moved northward out of South America and into Canada.It is often asserted that the Virginia opossum is a living fossil, a survivor in North America for the last 75 or 100 million years, but in truth this species is one of the most recent arrivals from South America. Both genetic and geological evidence indicate that this species has evolved only since the last Pleistocene glaciations, which ended between 15,000 and 10000 years ago.and its arrival in North America is even more recent. The Virginia opossum is a relatively recent immigrant to Canada. Prior to the European colonization of North America, the northern limit of this opossum was Virginia and Ohio. This opossum is one of the few animals that has benefitted from the changes wrought by the agricultural transformation of North America. The extermination of large predators, such as pumas, wolves, and fishers in the eastern United States and southeastern Canada has allowed this opossum to multiply and extend its range. Virginia opossums will eat almost anything, and it is safe to say that the garbage generated by human settlements, a share of vegetable and fruit crops, and a rise in various smal-mammal populations associated with land clearing have all increased the amount of food available to them. In any case, the Virginia opossum has experienced a kind of ecological release, allowing it to increase its range both north and south.
6.The word “relatively” in the passage is closest in meaning to
A.possibly
B.obviously
C.apparently
D.comparatively
7.According to paragraph 4, which of the following is true of the Virginia opossum?
A.It now lives primarily in Virginia, Ohio, and Canada.
B.It has expanded its territory during the last 10,000 years.
C.It has remained essentially unchanged for at least 75 million
years.
D.It has ceased to live in South America as a result of the last Pleistocene glaciations.
8.According to paragraph 4, why is it wrong to consider the Virginia opossum a living fossil?
A.It is descended from marsupials with a long history of contact with placental mammals.
B.It evolved only after the last Pleistocene glaciations.
C.It arrived in North America after European colonization.
D.It has responded positively to environmental changes made by humans.
9.Look at the four squares [▊] that indicate where the following sentence could be added to the passage.Where would the sentence best fit?
These geographic changes set in motion biological changes.
10.Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Although both marsupials and placentals are mammals, they differ significantly from one another.
A.Physical differences and evolutionary history explain why marsupials are considered more primitive than placentals.
B.With the reconnection of North and South America, marsupials diversified into a wide variety of life forms.
C.Despite evidence to the contrary, the Virginia opossum is widely regarded as a living fossil.
D.Even though marsupials and placentals began to develop physical differences early in mammalian history. differences in their reproductive system and strategy are recent.
E.Marsupials survived in many parts of the world only as long as there was little or no competition from placentals.
F.Some marsupials have evolved over time, and, in North America,opossums have spread over large areas due to human activity in the region.
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