A fossil recently discovered in Marlandia, a chain of islands, proves

A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. - A fossil was recently discovered. The fossil links the lineage of a current reptile with an ancient reptile that lived in the same area many years ago.

The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago. - The author is surprised by this finding since the ancient species was presumed to have become extinct when the area was submerged a few million years ago (The surprising part is that if the ancestral species had become extinct, how do we have its living descendants!)

Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged. - Given this surprising finding, many scientists have concluded that the entire area must not have submerged (and thus the ancestral species may not have become extinct at that time.)

Gist:

The passage talks about certain reptiles in a particular chain of islands.

Recent development: A discovered fossil proves that a current species is descended from an ancient one.

Previous understanding: People used to believe that the islands had completely submerged in the past, making the ancient species extinct.

The coexistence of these two scenarios is surprising.(support), Thus, many scientists conclude that the islands must not have entirely submerged (conclusion).


The argument assumes that if the islands had entirely submerged, the species could not have survived. What if the ancestral reptiles survived at sea? If the ancestral reptiles survived at sea, we’d have living descendant of the ancestral reptiles. In such a case, we’d have no basis to say that a part of Marlandia remained unsubmerged.

What if the ancestral reptiles migrated elsewhere, and then the descendants came back and resettled? In such a case too, we wouldn’t be able to arrive at the conclusion of the argument.

The argument also assumes that if an ancestral species goes extinct, it cannot have subsequent descendants. What if, there were some interim species that eventually led to the living descendants?


We’re looking for additional support for the scientists’ conclusion that the entire area must not have submerged. We can strengthen the argument by supporting any of the assumptions we figured above.


A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.
Incorrect. Good for the reptiles! Did some adaptation come about from a complete submerge? Was there a complete submerge? Nothing here gives us a concrete answer for either of these questions.

B. Marlandia separated from a much larger landmass about eighty million years ago.
Incorrect. How the islands came into being has got nothing to do with the argument at hand.

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.
Incorrect. Let’s consider the following statement:
Fossils of the ancestral species have been found at places other than Marlandia. (This statement is quite different from the one above, but stay with us a bit.)
Does this statement WEAKEN the argument?

It does. It indicates that the ancestral species perhaps relocated elsewhere and then the species or their descendants came back to Marlandia, thus making us doubt the hypothesis that the species must have survived in Marlandia itself, and thus weakening the conclusion that the islands must not have completely submerged.

Ok, let’s consider the following variation next:

Fossils that prove the relationship between the ancestral species and the present day species have been found at places other than Marlandia.

Does this statement WEAKEN the argument?

What does finding such fossils that ‘prove the relationship’ tell us? Do we know what type of fossils prove the relationship? Can only fossils of ancient reptile species prove this relationship? Couldn’t fossils of some other species help prove the relationship between the present-day and ancestral species? For example, couldn’t there be some indicative gene discovered in a fossil of species Z that helps prove a relationship between species X and Y? We do not know anything about what kind of fossils could prove the relationship. Thus this variation does not weaken the argument.

Now, let’s consider the option mentioned and discuss whether it STRENGTHENS the argument.

The fact that fossils that ‘prove the relationship’ haven’t been found does not increase our belief that the ancient species did not migrate (and as a consequence the belief that the sea-level rise left at least part of Marlandia unsubmerged.)

In addition, even if archaeologists were looking for such fossils, not finding does not equate to not being present. Fossils are difficult to find. Maybe they are out there, just that they haven’t been found yet.
D. The present-day reptiles are able to thrive on very tiny Marlandia islands.
Incorrect. Good for them! Happy to hear that the present-day reptiles are able to thrive. The argument is about whether the islands submerged and how the ancestral reptiles survived. This option does not support the argument at all.

E. The ancestral reptiles could not have survived long at sea.
Correct. Had the islands been completely submerged, this option suggests, the ancestral reptiles could have gone extinct (since the possibility of surviving at sea is taken away). Since, in such a case, we wouldn’t find their descendants, an expectation that doesn’t match with the reality, it is likely that the islands were not completely submerged. This option does support the conclusion.


Remember: ‘To support’ does not mean ‘to confirm’. Option E does not confirm that the islands were not completely submerged. It does increase the probability, though.

If you have any doubts regarding any part of this solution, please feel free to ask.

Official Explanation

Argument Construction

This question requires that we identify the answer choice that lends the most support for the scientists' conclusion. This conclusion states that the islands of Marlandia must not have been completely submerged during a global rise in sea level as had previously been thought.

Scientists arrived at this conclusion after being surprised to find that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. They had believed that this prehistoric species had become extinct millions of years ago when Marlandia was submerged due to a global rise in sea level.

What are some ways that we can strengthen support for the conclusion? Information that rules out the possibility that the reptile could have survived even if the islands had been completely submerged would strengthen support. So would information that rules out the possibility that the reptile had migrated to somewhere other than Marlandia but traveled back to Marlandia after the islands were no longer submerged.

A. Even if it is true that reptiles on Marlandia have adapted to environmental changes since the sea-level increase, that does not support the belief that part of Marlandia never became submerged when the sea level rose. It does not rule out either of the two alternative explanations discussed immediately above, for instance.

B. The argument's conclusion is about whether some part of Marlandia never became submerged. Information indicating that Marlandia separated from a much larger landmass many millions of years before the global sea-level rise is not relevant to that conclusion.

C. It might seem that this choice supports the conclusion. If the ancestral species never lived anywhere other than Marlandia, then the present-day species could not have descended from this ancestral species elsewhere and only later, after the sea-level rise, migrated to Marlandia. That would help rule out an alternative explanation of how the present-day species survived the global sea-level rise. However, note that all we are told is that no fossils have been found anywhere other than Marlandia. Simply because no such fossils have yet been found does not indicate that these ancestral species never existed elsewhere. Fossils are often deeply buried and hard to find. After all, the fossils on Marlandia that are discussed in the argument were only recently found; perhaps other such fossils will soon be found elsewhere. Thus, this answer choice does not support the conclusion.

D. This does not provide any particular support for the argument. Note that it is not the present-day reptile species that is presumed to have survived on Marlandia when sea levels rose. Rather, it is the ancestral species that is presumed to have survived.

E. Correct. This rules out that the ancestral species could have survived the sea-level rise simply by living at sea. It also reduces the possibility that the ancestral species had also lived elsewhere than Marlandia and had only later—after the sea-level rise—migrated to Marlandia.

The correct answer is E.

First, let’s consider the structure of the passage:

• Scientists conclude that the sea-level rise 25 million years ago left part of Marlandia unsubmerged.
• This is because a fossil proves that present-day Marlandian reptiles descend from ancient species that lived on the island millions of years ago.
• Previously, the ancestral species was thought to have gone extinct during the sea-level rise.

But the scientists seem to have made a jump in their reasoning. Just because the species continued after the sea-level rise does not necessarily mean that part of Marlandia was unsubmerged. What if the ancient species survived the sea-level rise in another way?

The question asks that we find an answer choice that provides the most support for the scientists’ conclusion. With that in mind, let’s take a look at the answer choices.


(A) gives us information about what has happened since the sea-level rise, but we’re concerned with what happened during the sea-level rise. Moreover, it merely gives us information on reptiles in general, and we don’t know whether it applies to this particular species. Eliminate (A).


If Marlandia previously separated from a larger landmass, we may have some reason to believe that the ancient species was originally found on that landmass. But the fact that Marlandia separated from a larger landmass 80 million years ago gives us no reason to believe that Marlandia was left unsubmerged 25 million years ago. Eliminate (B).


(C) tells us that the only proof of a relationship between the ancient and present-day species has been found in Marlandia. This may make us think that the relationship between the two species is unique to the island. But we don’t actually know that for sure. All we know is that our existing proof only supports the relationship on Marlandia. And it still does not provide support for the idea that part of Marlandia was left unsubmerged. Eliminate (C).


The problem with (D) is that we don’t know whether the present-day reptiles are able to thrive on other islands as well. If they were only able to thrive on the tiny islands, then maybe we would have reason to believe that those islands were left unsubmerged. But we don’t actually know that, and it’s possible that the reptiles are able to thrive in many places. So, we can eliminate (D).


(E) is interesting. If the ancestral reptiles could not have survived long at sea, then we have reason to believe that the reptiles would not have survived if the entirety of the Marlandia islands were submerged. Because the reptiles did survive, (E) makes us think that at least part of Marlandia was unsubmerged. Therefore, (E) supports the scientists’ conclusion, and it is the best answer choice.
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A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.

If the ancestral reptiles can adapt, then they probably made it through the sea level rise. Weakens

B. Marlandia separated from a much larger landmass about eighty million years ago.

Irrelevant since the sea level rise is thought to have happened only 25 million years ago

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.

Irrelevant

D. The present-day reptiles are able to thrive on very tiny Marlandia islands.

Irrelevant

E. The ancestral reptiles could not have survived long at sea.

If the ancestral reptiles could not have survived at sea and they have present day descendants, the ancestral reptiles probably didn't have to survive at sea. This should mean that some part of Marlandia wasn't submerged. Strengthens

Answer is (E)
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A fossil recently discovered in Marlandia, a chain of islands, proves that a present-day reptile indigenous to Marlandia is descended from an ancient reptile species that lived on the islands millions of years ago. The finding is surprising since the ancestral species was thought to have become extinct when Marlandia was submerged in a global sea-level rise twenty-five million years ago. Based on the new discovery, many scientists have concluded that the sea-level rise in question left at least part of Marlandia unsubmerged.

Conclusion - Some part of Marlandia was unsubmerged when the sea-level rose.
In all the answer choices, we have to find the strengthener of this statement.

Which of the following would, if true, provide the most additional support for the scientists' conclusion?

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise. - Doesnt say anything about conclusion.

B. Marlandia separated from a much larger landmass about eighty million years ago. We are talking about 25 million years old issue here

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia. - No talk about conclusion

D. The present-day reptiles are able to thrive on very tiny Marlandia islands. - I initially marked this as it proves that the reptiles can survive even on tiny islands. so, take it as a contender

E. The ancestral reptiles could not have survived long at sea. - This shows that reptiles would have to survive at land as it cant survive in sea for sure. So, this definitely proves our conclusion.

Out of D and E, E is a better choice.

Adaptability – irrelevant

We are not interested in what was done 80m y ago – only about THAT sea level rise…

its narrowing the location where species can be found, but nothing about parts submerged

Irrelevant

If sea risen – reptiles submerged died – only unsubmerged species survived – it is

I would like to ask choice (E). What if the "unsubmerged part of Marlandia" is the separate part of another big land and the ancestral reptiles live just in that small part of the big land? Because if the above is true, then there is no need for the ancestral reptiles to be able to survive long at sea. In fact, they lived on the land and were "shipped" to where the land now is with the land movement.

"Unsubmerged part of Marlandia" is the separate part of another big land - If we assume than it would be ""Unsubmerged part of big land" not of Marlandia islands.

Need to keep our assumptions limited to given stem and information.

Thanks, I think I got the point. The question mentioned only Marlandia island, but I overextended the object being discussed, mistakenly "merged" other island into Marlandia.

Option C is a weak attempt to rule out an alternate explanation. The info is inconclusive! Suggests that the species could have not existed elsewhere during the time of the flood solely because no fossils were found yet. One can safely see how this isn't convincing. Close, but out for the doubts that could question its validity such as - What if in the future fossils are found?
Option E is straightforward. It says that the species would never have survived the sea-level rise. An evolution wouldn't have been possible with such a threat. Hence, there must have been some land on the island that wasn't affected by the sea-level rise.

GMATNinja
Can you please help with this?

Earlier Belief: Marlandia was completely submerged millions of years ago.
New Discovery:Fossils of an ancestor of an indigenous to Marlandia.
Conclusion:Marlandia was not completely submerged.
Gap:How does discovery of the fossils of the ancestor relate to the island not being submerged.
Assumption:Reptiles(ancestor) could not have survived on the submerged island.
Now the questions asks us to find a choice that strengthens the conclusion. So if we find find something that fills the gap or supports the conclusion, then we are done.
Now coming to the options:
A)If they have adapted then maybe they also survived on the submerged island. Weakens
B)No relation to the argument.Irrelevant
C)Even if fossils were found, that isn't related to submersion.
D)Current reptiles can thrive on small lands and maybe the ancestor also needed land or maybe not(no proof),this option doesn't strengthen the conclusion.Neutral
E)This option perfectly fills the gap. They could not have survived, so this increases the probability that there must have been some unsubmerged part. Correct

Hi Experts,

please help in understanding the argument and why is option E correct

GmatNinja VeritasKarishma

Thank you

Manisha_1991 you gotta tag them so they can see .

GMATNinja

VeritasKarishma

We need to keep a couple of points in mind before eliminating the answer choices:
1. The present day species is indigenous to Marlandia
2. It has been proved without any doubt that the present day species is a descended from the ancient species (evidence is the fossil record)
3. The event happened 25 million years ago

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise - Incorrect
1. This option does not tell us what those environmental changes are
2. Also, it does not help us conclude whether a small piece of Malandia was left unsubmerged after the rise in sea level 25 million years ago

B. Marlandia separated from a much larger landmass about eighty million years ago - Incorrect
The event in question happened 25 million years ago, hence what happened 80 million years ago is irrelevant

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia - Incorrect
This one goes against the evidence in point #1 and #2 from the list mentioned at the start of this explanation

D. The present-day reptiles are able to thrive on very tiny Marlandia islands - Incorrect
This tells us that present-day reptiles have adapted to present day conditions, but this option does not tell us whether a small piece of Malandia was left unsubmerged after the rise in sea level 25 million years ago

E. The ancestral reptiles could not have survived long at sea - Correct
1. In point #2 we have non debatable evidence that the present day reptiles have descended from the ancient reptile species
2. Negating this option tells us that if there was no land then these species would have gone extinct and hence there would have been no descendants
3. Negating breaks down the argument

Ans. E

A fossil has been found in Marlandia, an island.
It shows that an indigenous present day reptile descended from an ancient reptile that lived here (so perhaps the fossil has unique features of both).
This is surprising because the ancient reptile was though to have become extinct 25 million yrs ago when Marlandia got submerged.

Conclusion - Some parts were not submerged.

We need to strengthen this.

A. Reptiles in Marlandia have adapted to many environmental changes since the sea-level rise.

Doesn't say anything about whether all of Marlandia could have been submerged or not.

B. Marlandia separated from a much larger landmass about eighty million years ago.

Irrelevant how Marlandia came into being.

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.

No fossils have been found elsewhere does not mean they don't exist elsewhere. We are not given that the ancient reptiles lives only on Marlandia. Perhaps the fossil reptiles came to Marlandia and then the present day reptiles descended from them. Though to a small degree, it does increase the probability that some parts of Marlandia were not submerged but finding fossils is such a rare occurrence that not finding elsewhere has little meaning. Let's hold this.

D. The present-day reptiles are able to thrive on very tiny Marlandia islands.

Irrelevant.

E. The ancestral reptiles could not have survived long at sea.

This does help to strengthen that some parts of Marlandia were not submerged. If the ancient reptile could not have survived long at sea, it could not have stayed in the sea and then come back to Marlandia when it rose up again. This also means the ancient reptile could not have swum somewhere else and then come back to Marlandia once it rose again. Hence, it does become more likely that some land of Marlandia must not have been submerged.


Also, now looking at option (C) again (while ignoring option (E)), we know that it doesn't strengthen the conclusion. The ancient reptile could have swum to other land and returned to Marlandia once it rose again. So not finding fossils elsewhere doesn't help us.

Answer (E)
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What
that the sea-level rise in question left at least part of Marlandia unsubmerged.
Why
- ancestral species thought to have become extinct when island was submerged.
If the ancestral species became extinct, they should have no future generations.
- But species did not become extinct as the fossil links ancestral reptiles to current reptiles (future generations)

Thought process
Discovery Indicates 2 things one is it links the current reptiles to ancestorial ones and implicitly means that ancestry was not extinct at the time the island submerged.

So since the ancestry survived (this inference is essential to make) at least part of the Marlandia unsubmerged.
Gap: Assumption. Ancestry could not survive at sea.
If ancestry survived sea, conclusion breaks else conclusion holds.

E. The ancestral reptiles could not have survived long at sea.
As per our thought process

C. No fossils that prove the relationship between the present-day species and the ancestral species have been found anywhere other than Marlandia.
Just for knowledge one can infer - No fossils have been found doesn’t mean they do not exist.

But the reasoning is not about the fossils, it is the ancestry surviving sea or not.

C implies fossils that prove… have not been found elsewhere. Only found in Marlandia.
This Marlandia could have been completely submerged or unsubmerged.
The creature could have survived both cases (We know the ancestry surely survived. It is proved “the fossils prove” )
In short the choice doesn’t tell us that ancestry was allergic to sea and no sea was essential to their survival.

You are confusing the things, please read Karishma Mam's explanation for clarity
Conclusion is that some portion of Islands are unsubmerged as per the discovery
Option E indicates that ancient reptiles could not survive long at sea, so ancient reptiles could become extinct if it were on sea as it cannot swim, neither it can escape from sea and reach Marladia Islands. So it gives us a possibility that a portion of Island was unsubmerged and ancient reptiles were able to survive and present day reptiles descended from them

Option C is incorrect as no fossils were found does not means that fossils do not exist elsewhere. May be some fossils exist at some other place and ancestral reptiles existed in past at those other places

Subject: A fossil recently discovered in Marlandia, a chain of islands, proves




Hey yes I did not specifically mention but i am against option C too.
I basically mean what can be inferred or what choice C means.
Correct answer is SURELY E.

What my post pertains to is the relevance of the fossils.

Premises say

Earlier
The ancestry was supposed to be extinct. Implies that the current day reptiles had unknown ancestry till the finding.

After finding fossils
The fossil found links the ancestry to the current day reptiles. This is surprising because the ancestry was thought to be extinct in the submerging, but post this finding the ancestry is established.

"It also establishes that the ancestry was present at the time of submergence AND survived it because thats how the current day reptiles came in to existence."
My earlier post is all about the above statement.

Conclusion
Therefore at least part of the island was not submerged.

Can it really be drawn that at least part of the island was not submerged.
What if the specimen in fossil could survive at sea.

I am in complete agreement with Karishma mam. Her explanation is always flawless. I just didn't mention the correct answer explicitly.

This explanation is my opinion. Thanks