The fossil record shows that the climate of North America : GMAT Critical Reasoning (CR)
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# The fossil record shows that the climate of North America

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The fossil record shows that the climate of North America [#permalink]

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22 Sep 2010, 14:32
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The fossil record shows that the climate of North America warmed and dried at the end of the Pleistocene period. Most of the species of large mammals then living on the continent became extinct, but the smaller mammalian species survived.
Which of the following, if true, provides the best basis for an explanation of the contrast described above between species of large mammals and species of small mammals?

(A) Individual large mammals can, in general, travel further than small mammals and so are more able to migrate in search of a hospitable environment.
(B) The same pattern of comparative success in smaller, as opposed to larger, species that is observed in mammals is also found in bird species of the same period.
(C) The fossil record from the end of Pleistocene period is as clear for small mammals as it is for large mammals.
(D) Larger mammals have greater food and space requirements than smaller mammals and are thus less able to withstand environmental change.
(E) Many more of the species of larger mammals than of the species of smaller mammals living in North America in that period had originated in climates that were warmer than was that of North America before the end of the Pleistocene period.

Please explain the reasoning, i do not see this one
[Reveal] Spoiler: OA
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22 Sep 2010, 14:41
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It is not explaining the contrast. In fact it contradicts the contrast by saying that the larger mammals can survive by migrating (A) Individual large mammals can, in general, travel further than small mammals and so are more able to migrate in search of a hospitable environment.

Irrelevant (B) The same pattern of comparative success in smaller, as opposed to larger, species that is observed in mammals is also found in bird species of the same period.

Irrelevant (C) The fossil record from the end of Pleistocene period is as clear for small mammals as it is for large mammals.

Only one providing a valid justification(D) Larger mammals have greater food and space requirements than smaller mammals and are thus less able to withstand environmental change.

It is not explaining the contrast. In fact it contradicts the contrast by saying that the larger mammals should be able to survive the warm temperatures (E) Many more of the species of larger mammals than of the species of smaller mammals living in North America in that period had originated in climates that were warmer than was that of North America before the end of the Pleistocene period.
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22 Sep 2010, 15:05
The gist of the argument is climatic changes caused extinction of most large mammal species but not of smaller mammalian species. One is trying to find a cause of this aberration. Looking at the options

A) This actually contradicts our premise. If large mammals can travel further then they would have immediately migrated to a hospitable climate. Incorrect.
B) It says a similar pattern was observed in bird species of the same period. So what? Now we got to understand why large birds died but smaller ones didn't. Be careful here and don't use correlation as causality.
C) It is just another piece of evidence that simply reinforces the premise but has no bearing on the conclusion.
D) Larger mammals cannot withstand environmental change. Bingo...right answer.
E) This is another attractive answer and it is always tempting to tick the longest answer. But the key point of "adaptability" is missing over here. It is simply stating that larger mammals originated in comparatively warmer climates. Why would that be a reason for larger mammals not able to adapt to warm and dry climate? Incorrect.
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22 Sep 2010, 15:51
You are asked to find a reason to explain why large mammals didn't survive while the smaller ones did. With this in mind, look at the answer choices.

tatane90 wrote:
The fossil record shows that the climate of North America warmed and dried at the end of the Pleistocene period. Most of the species of large mammals then living on the continent became extinct, but the smaller mammalian species survived.
Which of the following, if true, provides the best basis for an explanation of the contrast described above between species of large mammals and species of small mammals?

(A) Individual large mammals can, in general, travel further than small mammals and so are more able to migrate in search of a hospitable environment. Contradicts given view. This should mean that larger mammals survived better
(B) The same pattern of comparative success in smaller, as opposed to larger, species that is observed in mammals is also found in bird species of the same period. Not an explanation or basis, just an observation
(C) The fossil record from the end of Pleistocene period is as clear for small mammals as it is for large mammals. Substantiates evidence but does not provide any explanation
(D) Larger mammals have greater food and space requirements than smaller mammals and are thus less able to withstand environmental change. The only reason that provides an answer to the question WHY. Hence correct.
(E) Many more of the species of larger mammals than of the species of smaller mammals living in North America in that period had originated in climates that were warmer than was that of North America before the end of the Pleistocene period. Long and wordy and irrelevant

Please explain the reasoning, i do not see this one
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23 Sep 2010, 19:35
straight D
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23 Sep 2010, 21:28
Straight D.
It clearly says that larger mamals were gluttons and due to the drastic weather changes thy were unable to survive.
I don't say this is the best choice but better among the 5.
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23 Sep 2010, 23:31
clearly D.
Only it explains that the larger animals were not able to adapt to that environment.
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24 Sep 2010, 04:59
+1 for D
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24 Sep 2010, 18:11
+1 for D as well
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08 Oct 2010, 13:34
D for me
Re: Fossil north America   [#permalink] 08 Oct 2010, 13:34
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