LSAT 102 | Section 2 | Logical Reasoning: Q12

LR Question 12 Explanation

QUESTION TEXT: It has long been thought that lizards evolved from a group of…

QUESTION TYPE: Necessary Assumption

CONCLUSION: Lizards couldn’t have come from anthracosaurs.

REASONING: The oldest lizard fossil is older than the oldest anthracosaur fossil.

ANALYSIS: This is a bad argument. Fossils don’t necessarily tell us when a species first evolved. There could be an even earlier anthracosaur fossil that we haven’t found yet.

Note that the question stem says “that there are no“.

This is actually a very useful demonstration of how to answer a necessary assumption question. Normally you have to negate (make false) the answers yourself, but this question stem does it for you.

Just take each answer as is (without the no), and see if it wrecks the argument. Ask yourself: “If there are ______, does this wreck the argument?”

The one that does is the right answer, the argument must assume that it is not true.

___________

1. CORRECT. If this isn’t true, then anthracosaurs could be older than lizards. We just have to find the fossils that prove it.
2. If there were even older lizards fossils, then the argument would be stronger.
3. Actually, we do have a lizard fossil that predates anthracosaur fossils. We found a 340 million year old lizard fossil.
4. This just means that some anthracosaur fossils are older than some lizard fossils. It doesn’t change the fact that at least one lizard fossil is older than all anthracosaur fossils.
5. Who cares if some lizard fossils can’t be dated. That doesn’t change the fact that other lizard fossils can be dated, and that they are older than anthracosaur fossils.

Recap: The question begins with “It has long been thought that lizards evolved from a group of”. It is a Necessary Assumption question. Learn more about LSAT Necessary questions in our guide to LSAT Logical Reasoning question types.