#9 - Paleontologists have discovered fossils of centipedes

[Administrator]

Complete Question Explanation

StrengthenX. The correct answer choice is (D)

The centipede fossils are much older than the fossils which were, until now, thought to be the oldest land-dwelling animals. Also, nearby fossils were from water-dwelling animals. So how can the paleontologists say that these centipedes were land-dwelling?

Read the question stem carefully. Four of these answer choices will support the paleontologists' position. One answer choice, the correct answer choice, will not.

Answer choice (A): The well-adapted legs are good evidence for these centipedes being land-dwelling.

Answer choice (B): That all other previously known centipedes are land dwellers is good evidence for these centipedes being land-dwelling.

Answer choice (C): Perhaps the fossilized centipedes lived on mud flats, which are basically land, but occasionally water-dwelling animals were washed in with river water. Thus, this evidence is consistent with these centipedes being land-dwelling.

Answer choice (D): This is the correct answer choice. The paleontologists may want to argue, "Ignore those water-dwelling fossils. That's just a fluke, and we can explain it away." But all the previous fossils from land-dwelling animals were not found near fossils of water-dwelling animals. That fact makes the current case very suspicious.

Answer choice (E): The nearby spider fossils, which showed that the spiders could breathe only air and not water, is good evidence for these centipedes being land-dwelling.

[Tyler]

I just want to make sure my prephrase was good for this question.

I said "Something that doesn't help to prove centipedes lived on land".

I got the correct answer but would you have any suggestions on how I could have improved this prephrase?

Thanks!

[Jonathan Evans]

Tyler,

Actually, your prediction is more-or-less on the mark for this Strengthen-Except question. Here's the deal: when you have a Strengthen-Except or Weaken-Except question, you can anticipate that there will be a variety of ways to help or hurt the conclusion. When you have four incorrect answers that all help the conclusion, you can expect at least a couple "supporter" answer choices that provide new and different evidence to bolster the conclusion. There may also be one or two "defender" options that shore up the argument against potential weaknesses (answer choice (B) would be more of the defender-type here. (A), (C), and (E) are all supporters).

So what should you want out of a prephrase? In these cases, since the arguments are rather open-ended, you kinda want your prephrase to be broad enough to encompass different kinds of scenarios. Could you perhaps anticipate a couple possibilities? Sure. By all means. Should you rack your brain to exhaust all possible options? No way.

I'm on board with your prephrase here, as broad as it is. Other strengthen and weaken scenarios will require or benefit from a narrower analysis, but good job here!

[jmramon]

Hi! I was hoping I could get some guidance with this answer.

I got stuck between C and D. I thought C could be right, not for the reason the Admin stated, but because the river water could have brought the centipedes in to the land (the mud flats) and therefore indicate that the centipedes may be water-dwelling and not land-dwelling, undermining the paleontologists’ conclusion. I see that D could also provide no support by saying that the oldest known land-dwelling animal fossils didn’t contain water-dwelling animal fossils, so perhaps these new centipedes are either not the oldest or are not land-dwelling, or both, and thus weaken the paleontologists’ conclusion.
Would someone please be able to explain why my reasoning is faulty for assuming C provides the least support? Thank you

[Francis O'Rourke]

Answer choice (C) essentially allows us to ignore the evidence of water-dwelling animal fossils. Since the land was occasionally covered with river water, we would expect to find a mixture of land- and water-dwelling animal fossils there.

Since this fact discredits the only evidence that was provided that could weaken the paleontologists' conclusion, it strengthens their argument. What is interesting is that if we learned this fact in isolation, as you present it, then it would weaken the idea that the centipedes were land-dwelling. However, you must always read these answer choices in context of the argument given.

[ambarfe]

Hi! I have a question about this. I now understand why D is the correct answer (thanks!), but I’m hoping to not make this mistake again and I have a question about B. My thought process was basically: “aha! Just because something has been this way doesn’t mean it proves it!” Did I just completely confuse this with “just because X has been this way, it does not mean that X will continue to be this way”? Basically, was the first concept completely off, or did I just mis-apply it? Thank you!

[Malila Robinson]

Hi Ambarfe,
It sounds like you are confusing a Must Be True concept with a strengthen concept. In Must Be True you generally cannot bring in outside information, so in that case knowing that something has happened in the past doesn't mean it would continue. In Strengthen questions you can bring in any info that would strengthen the Stimulus. So in that case knowing that something has always been that way lends support to the possibility that that will continue.
Hope that helps!
-Malila

[ambarfe]

That’s great Malila, thank you so much!

[mthomp24]

I understand why A, B, C, and E all strengthen the conclusion, but I am still confused as to why D does not strengthen. Could someone please explain that again? Thank you!

[Jonathan Evans]

Hi, MThomp,

Answer choice (D) is tricky. It does bring up information relevant to the conclusion. The paleontologists conclude that the centipedes lived on land, even though the fossils were close to water-dwelling animal fossils.

What would happen to our conclusion if we knew that all the other early land dwelling animal fossils were found nowhere near water-animal fossils? Would we think it's more likely that the centipedes lived on land or less likely that the centipedes lived on land? If every other land dwelling animal fossil was nowhere near water-animal fossils, we would probably think it's less likely that these centipedes lived on land. After all, no other land animal fossil was near water animals.

Thus, this statement weakens the conclusion! It is an opposite answer. Since we are looking for the answer choice that is the least helpful to our argument, this one is it. It hurts our argument and does not help it at all, so it is the credited response.

I hope this helps!