Logical ReasoningDifficulty: Hard

PT16 S3 Q18 Explanation

Because dinosaurs were reptiles, scientists

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsWeaken

Keep going in LSAT Lab

  • Save & drill this skill build targeted practice sets from questions like this one

  • Video walkthroughs watch every question solved step by step

  • 81 official LSATs as questions, timed sections & full-length tests

Full official LSAT questions are available through LawHub. This page provides LSAT Lab's explanation, strategy, and review tools without republishing the full official question.

Stimulus

Because dinosaurs were reptiles, scientists once assumed that, like all reptiles alive today, dinosaurs were cold-blooded. The recent discovery of dinosaur fossils in the northern arctic, however, has led a number of researchers to conclude that at least some dinosaurs might have been warm-blooded. These researchers point out that only warm-blooded animals whereas cold-blooded animals would have frozen to death in the extreme cold.

What this question is testing

Weaken

Your task

Find the choice that makes the argument's conclusion less likely to be true.

Common trap

Answers that look negative but attack a claim the argument never relied on.

Winning move

Find the assumption the argument depends on, then pick the choice that undermines it.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
18.

Which one of the following, if true, weakens the

Answer choices

  1. No Impact5% picked this

    Today’s reptiles are generally confined to regions of temperate or even

    We already know reptiles are cold-blooded and thus try to avoid cold climates. This doesn't tell us anything useful for figuring out these old dinosaur fossils.

  2. No Impact5% picked this

    The fossils show the arctic dinosaurs to have been substantially smaller than other known

    The fact that these dinos seem to have been "way smaller" doesn't seem to provide an alternate explanation for how dinosaurs could survive the arctic winter, nor does it seem to provide a way to say "it's implausible that they were warm blooded dinosaurs".

  3. Opposite (if anything)17% picked this

    The arctic dinosaur fossils were found alongside fossils of plants known for their ability to

    One potential alternate explanation for the dino fossils is that the Arctic area where the fossils were found wasn't actually cold back in the time of the dinosaurs. We wouldn't need to assume that dinos were warm-blooded if that area were just warmer than it is now. But the presence of plants able to withstand extreme cold makes it seem like the arctic WAS still wicked cold. So that would strengthen the argument, if anything.

  4. Correct66% picked this

    The number of fossils found together indicates herds of dinosaurs so large that they would need to migrate to

    Why this is right

    This provides an alternate explanation for the fossils in the arctic. They didn't belong to warm-blooded dinosaurs who lived there all year and survived the frigid winters. They belonged to regular cold-blooded dinosaurs who migrated through the arctic circle during its warmer months. Some dinosaurs would naturally die along the way, so that's how their fossils could end up in that habitat.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

  5. Opposite Impact7% picked this

    Experts on prehistoric climatic conditions believe that winter temperatures in the prehistoric northern arctic were not significantly different

    Like with (B), this helps reassure us that the arctic WAS in fact still butt cold back in the day of the dinosaurs, which helps the author. It rules out the potential alternate explanation that we found dino fossils in the arctic because the arctic was actually pretty warm back in the day.

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free