LSAT 102 – Section 2 – Question 12

LSAT 102 - Section 2 - Question 12

June 1998

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT102 S2 Q12
+LR
Necessary assumption +NA
A
89%
166
B
1%
158
C
2%
157
D
7%
159
E
1%
159
131
142
153
 +Medium 148.204 +SubsectionMedium

It has long been thought that lizards evolved from a group of amphibians called anthracosaurs, no fossils of which have been found in any rocks older than 300 million years. However, a fossil of a lizard was recently found that is estimated to be 340 million years old. Lizards could not have evolved from creatures that did not exist until after the first lizards. Therefore, lizards could not have evolved from anthracosaurs.

Summary
The argument concludes that lizards did not evolve from anthracosaurs. How do we know? Because we haven’t found anthracosaur fossils in rocks older than 300 million years, but we recently found a 340-million-year-old lizard fossil. And of course, lizards could have only evolved from creatures that predated lizards.

Notable Assumptions
The argument assumes that there are no anthracosaur fossils that are older than 340 million years. If such a fossil existed, the support for the conclusion would be destroyed, because we could no longer claim that lizards predate anthracosaurs.

A
unknown anthracosaur fossils older than 340 million years
The argument tries to establish that lizards predate anthracosaurs to conclude that lizards can’t have evolved from anthracosaurs. However if these fossils did exist, then we couldn’t establish that lizards predate anthracosaurs, so the conclusion would be unsupported.
B
unknown lizard fossils older than 340 million years
The argument relies on the idea that lizards predate anthracosaurs because of each group’s oldest known fossils. Having even older lizard fossils wouldn’t change this, so like (E), this isn’t necessary.
C
known lizard fossils that predate some anthracosaur fossils
The argument explicitly states that we now know of a lizard fossil which predates even the oldest anthracosaur fossils, so this assumption would just be contradictory.
D
known anthracosaur fossils that predate some lizard fossils
The argument relies on the ages of the oldest known fossils for each group, so just saying that some anthracosaur fossils predate some lizard fossils is irrelevant.
E
known lizard fossils whose age is uncertain
Like (B), this is irrelevant because the argument has already established that the oldest known lizard fossil predates the oldest known anthracosaur fossil, and this doesn’t add anything useful.

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LSAT PrepTest 102 Explanations

Section 1 - Reading Comprehension

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

Section 4 - Logical Reasoning

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