LSAT 17 | Section 3 | Logical Reasoning: Q21

LR Question 21 Explanation

QUESTION TEXT: Even the earliest known species of land animals…

QUESTION TYPE: Necessary Assumption

CONCLUSION: Early species of land animals must have evolved very rapidly after leaving an aquatic environment.

REASONING: The earliest known fossils of land animals were already quite adapted to life on land.

ANALYSIS: This argument exhibits a fairly common error on the LSAT: it mistakes the earliest known examples of something for the earliest example of that thing.

In plain English: There could have been land animals that existed long before 400 million years ago. We just haven’t found their fossils yet.

The argument is assuming that these animals emerged relatively recently from the ocean (since they were the first land animals).

___________

1. CORRECT. If the fossils don’t include fossils of animals that lived relatively soon after the emergence of land animals then this argument isn’t very good. It depends on the fossils having emerged relatively recently from the ocean. The conclusion was that the animals adapted very quickly to life on land.
2. It doesn’t matter what percentage of species the fossils represent. It only matters how recently those fossilized animals emerged from the ocean.
3. The stimulus is about land animals. Plants are irrelevant.
4. We only care about how animals adapted to life on land. It doesn’t matter if some eventually went back to the water as long as some stayed on land.
5. This isn’t necessary as long as some animals could be called land animals.

Recap: The question begins with “Even the earliest known species of land animals”. It is a Necessary Assumption question. Learn how to master LSAT Necessary questions on the LSAT Logical Reasoning question types page.