Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated

Hello Everyone!

Let's take a look at this question, one issue at a time, and narrow it down to the correct choice! To begin, here's the original question with the major differences between the options highlighted in orange:

Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles islands.

A. sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of
B. sloth, that they found in Puerto Rico in 1991, has been dated at 34 million years old, thus making it the earliest mammal known on
C. sloth that was found in Puerto Rico in 1991, was dated at 34 million years old, making this the earliest known mammal of
D. sloth, found in Puerto Rico in 1991, have been dated at 34 million years old, making the sloth the earliest known mammal on
E. sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of

After a quick glance over the options, a few key differences jump out:

1. Comma placement and verb choice after "sloth" (essential vs. non-essential clauses)
2. dated / has been dated / was dated / have been dated (verb tense)
3. made it / making it / making this / making the sloth / made the sloth (verb tense & pronouns)
4. of / on / known on (idioms)

Let's start with #1 on our list, which is to focus on how each sentence handles essential and non-essential clauses. Whenever we see a phrase in the middle of a sentence that's between two commas, it's supposed to be a non-essential clause.

This means that if we removed the phrase, the sentence would remain a complete sentence and wouldn't lose its intended meaning. A quick way to check this is to cross out any non-essential clauses you can find, and read what's left over. If it still makes sense, keep it for later. If it becomes a sentence fragment, or the meaning is totally changed, eliminate it. To make this easier, I've added in the non-underlined portions of the sentence:

A. Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles islands.

This is INCORRECT because the meaning of the sentence is altered by taking out the phrase "and dated at 34 million years old." By removing that phrase, we're simply saying that the presence of sloth fossils found in 1991 is enough proof that they are the earliest known mammals on the islands. But how do we know that? Because they were dated at 34 million years old. If we remove that bit of information, what's left over is vague and confusing for readers.

B. Fossils of the arm of a sloth, that they found in Puerto Rico in 1991, has been dated at 34 million years old, thus making it the earliest mammal known on the Greater Antilles islands.

This is INCORRECT because when we eliminate the non-essential clause, we can clearly see that there is a subject-verb agreement problem. This sentence uses the singular "has been dated" with the plural "Fossils," so let's rule this one out.

C. Fossils of the arm of a sloth that was found in Puerto Rico in 1991, was dated at 34 million years old, making this the earliest known mammal of the Greater Antilles islands.

This is INCORRECT because, if we read the sentence with the non-essential phrase crossed out, it doesn't make sense. It's actually missing a verb! Therefore, let's eliminate this option.

D. Fossils of the arm of a sloth, found in Puerto Rico in 1991, have been dated at 34 million years old, making the sloth the earliest known mammal on the Greater Antilles islands. --> OKAY

E. Fossils of the arm of a sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of the Greater Antilles islands. --> OKAY

We can eliminate options A, B, & C because they have problems when dealing with non-essential clauses.

Now that we've narrowed it down to 2 options, let's take a closer look at what we have left:

D. sloth, found in Puerto Rico in 1991, have been dated at 34 million years old, making the sloth the earliest known mammal on

This is CORRECT! The non-essential phrase, "found in Puerto Rico in 1991" truly is a non-essential piece of information. The important points (fossils were found, they were dated at 34 million years old, we now know they were the earliest mammals from the island) are all there and punctuated correctly. The sentence also uses the correct verb tense "have been dated" to show that the fossils were dated after they were found, but before the present, which is what we're looking for. It also correctly uses "making" to turn the last clause into an -ing modifier that refers back to the previous phrase, which is what we're looking for.

E. sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of

This is INCORRECT for one main reason - it contains two competing verbs! It correctly uses commas to make the phrase "found in Puerto Rico in 1991" a non-essential clause. However, it has two verb phrases (was dated at 34 millions years old / made the sloth the earliest known mammal...) without anything to connect them together. The last phrase should start with "making" to change it to a modifier that shows cause and effect. The fossils were dated at 34 million years old, and that led to them being known as the oldest mammals on the islands. Without the -ing modifier, it's unclear what actions led to what results.


There you have it - option D is the correct choice! This is an incredibly complex question, but if you can focus on the differences between the options, you can narrow down your options to only a couple you can focus on in more detail.


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