LSAT Explanation PT 19, S2, Q9: Ornithologist: The curvature of the claws

LSAT Question Stem

Which one of the following is an assumption on which the ornithologist's reasoning depends? 

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

The question type for this problem is a Necessary Assumption, which means we need to find an assumption that the ornithologist's argument depends on for it to be valid.

Let's first analyze the passage and identify the premises and conclusion. The ornithologist's argument can be summarized as follows:

Premise 1: The curvature of the claws of modern tree-dwelling birds enables them to perch in trees.

Premise 2: The claws of Archeopteryx show similar curvature.

Conclusion: Archeopteryx was probably a tree-dwelling creature.

The paleontologist counters this argument by pointing out that chickens can perch in trees but are not tree-dwelling, suggesting that the ability to perch in trees is not sufficient evidence to conclude that Archeopteryx was tree-dwelling.

Now, let's create an "Evaluate" question: "Did Archeopteryx actually use the curvature of its claws to perch in trees?"

With this in mind, let's analyze each answer choice:

a) Modern tree-dwelling birds are the direct descendants of Archeopteryx.

This answer choice is not necessary for the ornithologist's argument because it concerns the ancestry of modern tree-dwelling birds rather than whether Archeopteryx was tree-dwelling itself. This choice is incorrect.

b) Archeopteryx made use of the curvature of its claws.

This is the correct answer choice. For the ornithologist's conclusion that Archeopteryx was tree-dwelling to be valid, it must be assumed that Archeopteryx used the curvature of its claws to perch in trees. If it did not, the conclusion would be invalid.

c) There have never been tree-dwelling birds without curved claws.

This answer choice is not necessary for the ornithologist's argument because it focuses on the characteristics of other tree-dwelling birds rather than Archeopteryx itself. The argument is based on the curvature of Archeopteryx's claws, not the absence of other characteristics in tree-dwelling birds. This choice is incorrect.

d) Archeopteryx was in fact the earliest birdlike creature.

This answer choice is not necessary for the ornithologist's argument because it concerns the chronological status of Archeopteryx rather than its tree-dwelling nature. Whether or not Archeopteryx was the earliest birdlike creature does not affect the conclusion that it was tree-dwelling. This choice is incorrect.

e) The curvature of the claws is the only available evidence for the claim that Archeopteryx was tree-dwelling.

This answer choice is not necessary for the ornithologist's argument because it focuses on the availability of evidence rather than the validity of the conclusion. The ornithologist's argument is based on the curvature of Archeopteryx's claws, not the exclusivity of this evidence. This choice is incorrect.

In conclusion, the correct answer choice is (b) Archeopteryx made use of the curvature of its claws, as it is a necessary assumption for the ornithologist's argument to be valid.