#4 - Paleontologists had long supposed

[Administrator]

Complete Question Explanation

Assumption. The correct answer choice is (D).

The argument presents evidence, in the form of computer models, that Diplodocus could not have used its neck in the way that paleontologists had long believed they did, to reach high-growing vegetation such as at the tops of trees. We also learn that the dinosaur could have bent its neck downward to eat vegetation off the ground, and even reach below ground level to eat underwater vegetation. From this evidence the author concludes that Diplodocus must have eaten vegetation at ground level or underwater, rather than stuff much higher up.

The question stem asks us to identify an Assumption required by the argument, which means we must find an answer that the author has to believe is true in order for their argument to hold up to scrutiny.

The argument depends on at least two assumptions, and students might prephrase either or both before proceeding to the answer choices. For one thing, whenever we see that a conclusion is based on a study, experiment, or other data, the author must assume that the data is valid. Here, that means assuming that the computer models are correct. Also, the author concludes that because something could be true (Diplodocus could eat food at or near the ground or underwater), that it must be true, and this requires the assumption that that there is no alternative, no other way for the dinosaur to eat food that is found higher up than to raise its long neck.

Answer choice (A): While answer A might strengthen a claim about what Diplodocus ate, it is not a required assumption of the argument. It is possible that no modern animals have a similar neck structure, even if the author's argument is correct.

Answer choice (B): This is a completely unnecessary and irrelevant claim. It may or may not be true, but it has no bearing on whether the argument as presented is valid, and the conclusion could still follow from the premises even if Diplodocus could see in front of itself easily.

Answer choice (C): Like answer A, this could strengthen the claim that Diplodocus did not raise its head to eat leaves from treetops, but the argument does not require this to be the case. Even if an animal as large as this one could supply blood to an elevated brain, it still might be unable to get food from treetops and therefore eat only from supplies near ground level.

Answer choice (D): This is the correct answer choice. Answer D matches the second of our two prephrases above, that there is no alternative method for Diplodocus to gather food from high above ground other than to raise its neck. Try the Negation Technique on this answer and you get that it could have gotten that high-up food some other way, such as standing on its hind legs, which destroys the claim that it must have eaten food found down near the ground.

Answer choice (E): It would not matter to our author whether Diplodocus could kneel or not, or whether it could walk into lakes and rivers and forage for food there. The argument that it must have eaten only food found near or below ground level could still be valid whether it could kneel or not.

[christinecwt]

Answer choice (C): Like answer A, this could strengthen the claim that Diplodocus did not raise its head to eat leaves from treetops, but the argument does not require this to be the case. Even if an animal as large as this one could supply blood to an elevated brain, it still might be unable to get food from treetops and therefore eat only from supplies near ground level.

Hi Team - would you mind explaining why an animal still might be unable to get food from treetops even if it could supply blood to an elevated brain? so why Answer Choice C is wrong?

[atierney]

I would say answer choice C is a trap/shell type answer. The general rule is that necessary assumption answers should tie into the argument's conclusion, i.e. provide proof of the conclusion by addressing one of the core facts the conclusion relies. Here, while it may be implied that answer choice C encompasses a conclusion similar to answer choice D, i.e. if the blood could not be supplied to the dinosaur's elevated brain, then presumably there would be no way of accessing high growth vegetation; however, here is where we come to an unfortunate fact about the LSAT: In a choice between an answer that implies a condition and one that states such a condition at face value, take the latter.

It's a skill to read into things for sure, and I agree that the natural consequence of answer choice is something quite similar to answer choice D; however, rather than presuming this consequence, you should always take the answer choice that states it outright. And this somewhat makes sense because it begs the question of whether, regardless of the dinosaur's inability to elevate itself, there are other ways of accessing the vegetation, such as, waiting for the tree to fall down (in so far as the vegetation is still there) or waiting for another animal to drop it, etc. The point is that, in this particular section, the LSAT doesn't reward thinking in contingencies over recognizing outright the broader principle such a contingency conveys. We need to know C only because it implies D. Therefore, D is the principle or the necessary condition we are really after.

Let me know if you have any questions on this.