LSAT Explanation PT 22, S4, Q22: Dinosaur expert: Some paleontologists have claimed

LSAT Question Stem

The expert's argument depends on assuming which one of the following? 

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is D. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. The dinosaur expert is arguing against the claim that birds are descendants of a group of dinosaurs called dromeosaurs. The expert's conclusion is that the paleontologists' claim is false. The premise supporting this conclusion is that the earliest bird fossils date back tens of millions of years farther than the oldest known dromeosaur fossils.

To better understand the argument, imagine a simpler example. Suppose scientists claim that cats are descendants of a specific group of animals called "ancient cats," based on similarities between cats and ancient cats. However, the earliest cat fossils date back millions of years farther than the oldest known ancient cat fossils. In this case, the argument would be that the scientists' claim is false because the cat fossils are older than the ancient cat fossils.

An "Evaluate" question for this argument could be: "Do the known fossils accurately represent the relative dates of origin of birds and dromeosaurs?"

Now, let's discuss the question type and the answer choices. This is a Necessary Assumption question, which asks us to identify an assumption that the expert's argument depends on.

a) This answer choice is not necessary for the argument, as the expert's argument is based on the relative dates of fossils, not the similarities between the animals.

b) This answer choice is irrelevant to the argument, as the expert is focused on whether birds descended from dromeosaurs, not whether they share common ancestors.

c) This answer choice is tempting, but it is not necessary for the argument. Even if our knowledge of dromeosaur fossils and the earliest bird fossils is incomplete, the argument could still hold, as the relative comparison of the incomplete fossils still indicates that bird fossils are older than dromeosaur fossils.

d) This is the correct answer. The expert's argument depends on the assumption that the known fossils indicate the relative dates of origin of birds and dromeosaurs. If the known fossils do not indicate the relative dates of origin, then the premise would not support the conclusion.

e) This answer choice is irrelevant, as the expert's argument is based on the relative dates of fossils, not the similarities or dissimilarities between the animals.

In summary, the correct answer is D, as the expert's argument depends on the assumption that the known fossils indicate the relative dates of origin of birds and dromeosaurs. Other answer choices are either irrelevant or not necessary for the argument.