Paleontologists have discovered fossils of centipedes that are 414 million years old. These fossils are at least 20 m...

shunhe on July 31, 2020

Hi @JessicaR,

Thanks for the question! So let’s break down this stimulus real quickly. We’re first told that paleontologists have found these fossils of centipedes that are super old. 414 million years old, to be precise. And these are at least 20 million years older than the earliest land-dwelling animals previously identified. But the paleontologists are still confident that the centipedes lived on land, despite the fact that the centipede fossils were found in rock that also had fossils from water-dwelling animals.

So now we’re asked for something that would least support the truth of the paleontologists’ view; in other words, the thing that least strengthens the argument here. The ideal answer choice will either be irrelevant or weaken the argument. And the argument, remember, is that the centipedes live on land.

(A) tells us that the legs were good for moving on land. Well, that would make us think they did live on land, and strengthens the argument. (A)’s out.

(B) tells us that all the previous centipedes were land dwellers. Well, if the other ones were, then it’d make sense that these were too. This strengthens, and (B)’s out.

(C) tells us that the rock in which the centipede fossils were found was formed from mud flats that were sometimes covered by water. This one’s a bit weirder, but it still strengthens the argument. Why? Well, the centipedes could’ve lived on the mud flats (which are land), and then river water would’ve sometimes covered them. Which explains why the water-dwelling animals were found there, they got washed up when the mud flats were covered with river water. So this gives a reasonable explanation for the water-dwelling animals being there, which helps us think that the centipedes actually did live on land, so (C)’s wrong.

(E) tells us that fossils of spiders that could only breathe air were found in the same rock. Well, that means we found land animal fossils in the rock. Which suggests that there might be other land animal fossils, which would help us think that the centipedes are land animal fossils. So (E) is wrong.

(D) tells us that the fossils of the earliest land-dwelling animals were found in rocks that didn’t have the fossilized remains of water-dwelling animals. Well, that should make us think, why would we expect to find land-dwelling animals with these water-dwelling animal fossils? And so that casts doubt on the claim that the centipedes are land animals. Because this weakens,

Hope this helps! Feel free to ask any other questions that you might have.

JackM on March 10, 2023

Maybe i'm not understanding. Are you saying D is correct because they did not find water dwelling fossils on the same rock as the centipedes? Wouldn't that just make it more probable that the centipedes were land dwellers.

Or do we have to compare this answer to the stimulus. Are we saying the the fossils in E are the the same fossils found in the stimulus? Because if they are the same types of fossils, and there were no water-dwelling fossils on the rocks mentioned in D, then that would mean that those centipedes int he stimulus might have been water-dwelling?

Emil-Kunkin on March 12, 2023

D tells us that fossils of the other oldest land dwellers (that is not including the millipedes in the paragraph) were not found with water dwellers. This Would lead me to expect to find old land dwellers in rock that contains no water dwellers, not (as happens in the passage) in rock that contains water dwellers. This thus slightly weakens (or at very least does not strengthen) the argument that the millipedes were land dwellers.