LSAT 109 – Section 4 – Question 22

LSAT 109 - Section 4 - Question 22

December 2000

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Target time: 1:19

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT109 S4 Q22
+LR
+Exp
Necessary assumption +NA
Link Assumption +LinkA
Lack of Support v. False Conclusion +LSvFC
A
7%
158
B
3%
162
C
42%
166
D
48%
168
E
1%
161
150
168
180
 +Hardest 150.49 +SubsectionHarder

J.Y.’s explanation

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Dinosaur expert: Some paleontologists have claimed that birds are descendants of a group of dinosaurs called dromeosaurs. They appeal to the fossil record, which indicates that dromeosaurs have characteristics more similar to birds than do most dinosaurs. But there is a fatal flaw in their argument; the earliest bird fossils that have been discovered date back tens of millions of years farther than the oldest known dromeosaur fossils. Thus the paleontologists’ claim is false.

Summary
The author concludes that birds are not descendants of dinosaurs called dromeosaurs. Why? Because the earliest bird fossils that have been discovered date much further back in history than the oldest known dromeosaur fossils.

Notable Assumptions
The author assumes that the fact the earlier bird fossils are older than the earlier dromeosaur fossils proves that birds originated before dromeosaurs did.
The author assumes that there do not exist undiscovered dromeosaur fossils that are older than the earliest bird fossils that have been discovered.

A
Having similar characteristics is not a sign that types of animals are evolutionarily related.
The author doesn’t deny the idea that there’s an evolutionary relationship between birds and dromeosaurs. For example, the author could believe that dromeosaurs evolved from birds, or that they each evolved from a common ancestor.
B
Dromeosaurs and birds could have common ancestors.
Not necessary, because the author might believe there are no common ancestors between birds and dromeosaurs. All that the author is committed to about the relationship between the two is that birds did not evolve from dromeosaurs.
C
Knowledge of dromeosaur fossils and the earliest bird fossils is complete.
Too extreme to be necessary. The author doesn’t have to assume that our knowledge of the fossils is “complete.” The author just needs to assume that our knowledge of the fossils tells us that birds originated before dromeosaurs. Whether we’re missing a tooth from a skeleton or whether we’re missing some more recent fossils doesn’t affect the reasoning.
D
Known fossils indicate the relative dates of origin of birds and dromeosaurs.
Necessary, because if known fossils do NOT indicate the relative dates of origin, then what we know about bird and dromeosaur fossils doesn’t support a conclusion that birds couldn’t have evolved from dromeosaurs. After all, dromeosaurs could have originated before birds, so birds still could have evolved from them.
E
Dromeosaurs are dissimilar to birds in many significant ways.
Not necessary, because the author could agree that dromeosaurs are actually very similar to birds. That similarity may be due to dromeosaurs evolving from birds, or they both evolved from a common ancestor, or to pure coincidence.

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LSAT PrepTest 109 Explanations

Section 1 - Logical Reasoning

Section 2 - Reading Comprehension

Section 3 - Logical Reasoning

Section 4 - Logical Reasoning

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