LSAT 143 – Section 4 – Question 21

LSAT 143 - Section 4 - Question 21

June 2015

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT143 S4 Q21
+LR
+Exp
Weaken +Weak
Causal Reasoning +CausR
A
4%
158
B
1%
153
C
76%
165
D
15%
160
E
4%
157
139
151
162
 +Medium 146.108 +SubsectionMedium

In modern deep-diving marine mammals, such as whales, the outer shell of the bones is porous. This has the effect of making the bones light enough so that it is easy for the animals to swim back to the surface after a deep dive. The outer shell of the bones was also porous in the ichthyosaur, an extinct prehistoric marine reptile. We can conclude from this that ichthyosaurs were deep divers.

Summarize Argument
The author concludes that ichthyosaurs were deep divers. This is because ichthyosaurs share a feature with deep-diving mammals today: a porous outer bone shell. This feature is what helps deep-diving mammals surface after deep dives.

Notable Assumptions
The author assumes that the only function of the porous outer bone shell is to help animals surface after deep dives. If any given animal isn’t a deep diver, then it won’t have the porous outer bone shell feature.

A
Some deep-diving marine species must surface after dives but do not have bones with porous outer shells.
The author never says the porous outer bone shell is necessary for deep dives. It simply indicates that an animal is a deep-diver.
B
In most modern marine reptile species, the outer shell of the bones is not porous.
We have no idea if those reptiles are deep-divers.
C
In most modern and prehistoric marine reptile species that are not deep divers, the outer shell of the bones is porous.
Reptiles generally have porous outer bone shells despite not being deep divers. Since the ichthyosaur was a reptile, we can’t conclude if it was a deep diver.
D
In addition to the porous outer shells of their bones, whales have at least some characteristics suited to deep diving for which there is no clear evidence whether these were shared by ichthyosaurs.
We don’t need ichthyosaurs to have the exact same characteristics as whales. There are plenty of deep divers that aren’t whales.
E
There is evidence that the bones of ichthyosaurs would have been light enough to allow surfacing even if the outer shells were not porous.
This tells us that ichthyosaurs could’ve been deep divers even without the porous outer bone shells. We need to weaken the claim that ichthyosaurs were in fact deep divers.

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LSAT PrepTest 143 Explanations

Section 1 - Logical Reasoning

Section 2 - Reading Comprehension

Section 3 - Logical Reasoning

Section 4 - Logical Reasoning

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