Logical Reasoning

PT102 · S3 · Q9 Ornithologist: The curvature of the claws

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

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

Ornithologist: The curvature of the claws of modern tree dwelling birds enables them to perch in trees.

Conclusion

Archeo was probably a tree-dwelling creature.

Evidence

Archeo's claws had a curvature like that of modern tree-dwelling birds. This curvature enables modern birds to perch in trees. It would have enabled Archeo to perch on tree limbs.

Evaluate

Our author is assuming that because this curvature would have enabled Archeo to perch on tree limbs that the curvature was used for this purpose.

When author's look at a Curious Fact like "Why did Archeo have curved claws?" and then arrive at some Causal Interpretation like , we can always weaken with an Alternate Explanation.

Maybe they didn't live in trees and had curved claws for some other adaptive purpose (food gathering? defense against predators?)

Goal

Look for an answer that rules out an alternate explanation for the curved claws or an answer that provides something that would need to be true for it to be plausible that Archeo was a tree-dwelling creature.

Which one of the following is an assumption on which the ornithologist's reasoning depends?

Modern tree-dwelling birds are the
Too Strong
If modern tree-dwelling birds were indirect descendants of Archeo, is that going to be a big objection? No. The author is only establishing that Archeo is birdlike to add plausibility to the idea that Archeo used its curved claws to perch in trees like modern birds. She isn't trying to claim that modern birds descended directly from Archeo.
8% picked this
Correct
Archeopteryx made use of the
Why this is right
Haha, what a jerky correct answer. This falls into the category of "something that would have to be true for the author's story to be plausible". If we negate this, and Archeo "made no use of the curvature of its claws", then it would pretty much destroy the argument, since you can't really perch on a tree branch unless you curve your claws around the branch. The author was assuming a similarity between Archeo and modern birds -- we know they both have curved claws, and since modern birds use those curved claws to perch in trees, the author was assuming that Archeo similarly used its curved claws to perch in trees (which is how she arrived at the conclusion that it was probably a tree-dwelling creature). If Archeo never even used the curvature of its claws, then that assumption breaks down.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
68% picked this
There have never been tree-dwelling
Too Strong
The author's argument isn't going to be ruined if we negate this and say, "there was at least one species of bird that dwelled in trees but didn't have curved claws". The author is coming closer to assuming that "there has never been a bird that didn't dwell in trees that did have curved claws", but that would still be phrased too strongly.
16% picked this
Archeopteryx was in fact the
Irrelevant
It doesn't make any difference to the author's argument whether Archeo turns out to actually be the earliest birdlike creature. Whether it's the earliest or the 2nd earliest wouldn't change the argument in the slightest.
1% picked this
The curvature of the claws
Too Strong
Too Strong: only Only Thing Mentioned ≠ Only Thing In addition to curved claws, Archeo is identified as a birdlike creature (and many/most birds dwell in trees), so it's almost contradicted to say that curved claws are the only available evidence. But even if the paragraph hadn't said "birdlike creature" -- just because curvature of claws is the only evidence the author mentioned doesn't mean she's assuming it's the only evidence that exists. If we negate this, and say that "there is additional evidence for the claim that Archeo was tree-dwelling", that would help the author's argument, not hurt it.
8% picked this

Continue the review in LSAT Lab

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

Save and practice this skill

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