LSAT 109 | Section 4 | Logical Reasoning: Q22

LR Question 22 Explanation

QUESTION TEXT: Dinosaur expert: Some paleontologists have claimed that birds are…

QUESTION TYPE: Necessary Assumption

CONCLUSION: The paleontologists are wrong: birds did not descend from dromeosaurs.

REASONING: We have found bird fossils that are older than the oldest dromeosaur fossils.

ANALYSIS: Fossils don’t tell the whole truth. Suppose the oldest dromeosaur we found is 50 million years old. Does that mean that dromeosaurs didn’t exist 100 million years ago?

Not necessarily. We just might not have found the rights fossils. Or maybe the dromeosaurs that lived 100 million years ago didn’t leave any fossils.

___________

1. This supports the expert, but it isn’t necessary. You don’t have to be related if you have similar characteristics, even if they can be a sign of a relation.
2. This hardly matters. Whether or not birds and dromeosaurs have common ancestors, it’s still true that current bird fossils are older than dromeosaur fossils.
3. This would be a sufficient assumption, but it isn’t necessary. Suppose that our knowledge of fossils was complete, except for one bird fossil from 1 million years ago. Would that weaken the argument?
4. CORRECT. If this isn’t true, then our fossils prove nothing. Dromeosaurs might still be older than birds. We just haven’t found their fossils.
5. This supports the argument, but it isn’t necessary. The main point is that birds seem to be older than dromeosaurs.

Recap: The question begins with “Dinosaur expert: Some paleontologists have claimed that birds are”. It is a Necessary Assumption question. Learn more about LSAT Necessary questions in our guide to LSAT Logical Reasoning question types.