B,C,E out due to the S-V disagreement: fossils is a plural noun, thus it must be followed by a plural verb.
A is out with the wrong tense of "dated" ( it should be present perfect as the fact continues to the present.) . Besides, the use of "of" is wrong, "the earliest known mammal" must be the earliest of the same kind of thing, "islands" is not the same kind to " mammal".

D it is!

I’ve always had a soft spot for this question, just because it has such a wide variety of issues and errors. It also has an interesting little verb tense thing that really doesn’t matter at all: you could easily fixate on the difference between "was dated" (past tense) and "has/have been dated" (present perfect tense), but you don't have to choose between them at all. There are plenty of other issues to worry about instead.


The “it” (which presumably refers back to the sloth) is the first thing that jumps out at me. “Fossils of the arm of a sloth… made [the sloth] the earliest known mammal…” Huh? That makes no sense. How the heck would the fossils of a sloth make the sloth the earliest known mammal of the Greater Antilles?

The much smaller issue is that I see no real need for that first comma, but that’s unlikely to ever be a deciding factor on a GMAT question. But the nonsensical main clause is enough to wipe out (A).


This time, the pronoun “they” is the first thing that catches my eye. Who the heck is “they”? The fossils?

Plus, we have a subject-verb problem: “fossils… has been dated” is spectacularly wrong. (B) is gone.


Subject-verb fail again: “fossils… was dated.” Nope.

But there’s more: the phrase “that was found in Puerto Rico in 1991” seems to modify the sloth itself, and that makes no sense. Unless you think that the sloth had actually been alive for 34 million years. Maybe moving really slowly helps you live longer?

Finally, the word “this” is used as a singular pronoun, and that’s an unacceptable use of the word “this” on the GMAT. I’ve only ever seen “this” used as an article on the GMAT (“this week” or “this magnificent GMAT forum”), but never as a pronoun.

So we have lots of good reasons to eliminate (C).


This one looks pretty good. The subject-verb agreement works: “fossils… have been dated at 34 million years old…” Cool. The modifier “found in Puerto Rico in 1991” is nicely set apart with commas, so it seems to refer to the entire phrase “fossils of the arm of a sloth”, and not just the sloth itself, as we saw in (C).

And the last part of the underlined portion (“making the sloth the earliest known mammal…”) actually names the sloth instead of using a pronoun, and that adds a bit of extra clarity. It might not be strictly necessary, but it’s nice. We can keep (D).



Thanks to the modifier “which”, which typically modifies the immediately preceding noun, it really sounds like the sloth itself was found in Puerto Rico in 1991, and that makes no sense. (I also can’t make much sense of the comma placement in that part of the sentence, but again, comma placement isn’t really a major emphasis on GMAT SC.)

We also have the same problem that we had in (A): “fossils… made the sloth the earliest known mammal…” That’s nonsense, too.

So we can ditch (E), and (D) is our answer.

Can we reject (A) and (B) because of the use of "it" referring to a sloth. As in, the sentence is trying to say that a particular sloth was the earliest known mammal and not the whole species. To represent the whole species, the phrase the sloth should be used. Honestly I didn't realise the meaning on the basis of fossils and rejected (A) and (B) because of the difference between a sloth and the sloth. Can someone please tell me if this strategy or POE is correct?