During the first 140 million years of existence on earth, mammals were

Question

During the first 140 million years of existence on earth, mammals were relatively small, ranging from 2 to 22 pounds, but once the dinosaurs became extinct, mammals grew in size up to 1,000 times bigger and as large as 17 tons. Once the herbivorous dinosaurs were gone the mammals no longer needed to compete for space to roam and vegetation for food. They could eat all the food they wanted, and the larger mammals were better able to fend off predators. This is why we have our hippopotamuses and giraffes of today.

If the statements above are true, which one of the following must also be true on the basis of them?

(A) If the dinosaurs had lived longer, mammals today would be much smaller yet still herbivorous.

(B) If the hippopotamus we know today was a 1,000 times smaller, other mammals would also be significantly smaller.

(C) If other larger nonmammals had survived the event that made the dinosaurs extinct, modern mammals may have been much smaller due to competition for resources.

(D) If mammals had been larger during the time of the dinosaurs, the resulting competition would have made both extinct.

(E) If hippopotamuses and giraffes had evolved as carnivores and not herbivores, large mammals most likely would not have competed with the dinosaurs for space and food.

Bunuel · Accepted Answer

OFFICIAL EXPLANATION

Answer: C

STEP 1: Read the question and identify your task.

This is a Deduction question. It asks you to find a statement that must be true on the basis of the given statements.

STEP 2: Read the argument with your task in mind. 
The argument gives you a paleontological discussion concerning the survival of large mammals like the hippopotamuses and giraffes after the extinction of the dinosaurs.

STEP 3: Know what you’re looking for. 
The correct answer will most likely be a conclusion you can come to based on how such survival occurred, mainly the competition for living space and food.

STEP 4: Read every word of every answer choice. 
Answer A tries to relate a later timing of extinction to the smaller size of the surviving mammals, but nothing in the argument leads you to believe there is a relationship between the two, only that when it happened their size changed. The only thing you can assume is that the increase in size would have been delayed. With regard to answer B, the statements give no size relationship between the large mammals like the hippopotamus and other mammals. It tells only of large mammals and how they grew in size. Answer C is a very good option for your question. The statements discuss how the large mammals grew in size because they no longer had to compete for space and food with dinosaurs. Thus, you can assume that if larger nonmammals had survived the extinction event, they would have been competitors for space and food and the larger mammals would have been smaller. Answer D may be true, but nothing in the statements leads you to believe that the size of the dinosaurs had anything to do with their extinction. Answer E states something that cannot be verified by the statements. It is possible they would have competed with carnivorous dinosaurs and the same evolutionary process would have occurred. Answer C is the correct choice.

Adit_ · Answer

How is C better than B?

C talks about nonmammals when it is not a certainty that option C "must be true". I agree that there is the term "may" but drawing a causality relation of a different entity alltogether drawing the relation of size cant come under "must be true" right?

On the other hand there is a relation that since space to roam and more food was available to eat we have hippo and giraffes of today. So they explicitly cite two examples indicating animals that grew upto a massive size. This indicates a causality relation that hippo exists today because of more food and space to roam and that in general larger mammals exist because of the space and food to eat. Thus if hippos were indeed very tiny at the very least other mammals would be significantly smaller right?

Yes I do see the point being that if the mammals were already small then they would not be "significantly" smaller and the argument being that 2x relative size is coming down to 1.8x lets say as compared to a 100% decrease to 1x. And that there need not be such a correlation, but such a correlation could exist from the argument.

My overall point is even option C does not seem to be shell tight. I can't really say why is C better than B here. Neither statements seem to be "must be true".

Kindly help me out with further explanations/better clarity.  Bunuel

guddo · Answer

During the first 140 million years of existence on earth, mammals were relatively small, ranging from 2 to 22 pounds, but once the dinosaurs became extinct, mammals grew in size up to 1,000 times bigger and as large as 17 tons. Once the herbivorous dinosaurs were gone the mammals no longer needed to compete for space to roam and vegetation for food. They could eat all the food they wanted, and the larger mammals were better able to fend off predators. This is why we have our hippopotamuses and giraffes of today.
 
 If the statements above are true, which one of the following must also be true on the basis of them?

The passage says mammals became much larger after herbivorous dinosaurs disappeared because mammals no longer had to compete with them for space and vegetation.  So the supported idea is that if similar large competitors had remained, mammal size might have stayed more limited .

(A) If the dinosaurs had lived longer, mammals today would be much smaller yet still herbivorous.

This is too strong. The passage does not prove what mammals would be like today if dinosaurs had survived longer.

(B) If the hippopotamus we know today was 1,000 times smaller, other mammals would also be significantly smaller.

This is unsupported. The size of one animal does not determine the size of other mammals.

(C) If other larger nonmammals had survived the event that made the dinosaurs extinct, modern mammals may have been much smaller due to competition for resources.

This is correct. The passage says mammals grew larger after dinosaurs disappeared because competition for space and vegetation decreased. So if other large competitors had survived, mammals may have remained smaller.

(D) If mammals had been larger during the time of the dinosaurs, the resulting competition would have made both extinct.

This is far too strong. The passage says competition limited mammal size, not that competition would have caused extinction.

(E) If hippopotamuses and giraffes had evolved as carnivores and not herbivores, large mammals most likely would not have competed with the dinosaurs for space and food.

This is unsupported. The passage focuses on competition with herbivorous dinosaurs for vegetation and space, but it does not discuss this carnivore scenario.

Answer: (C)

RahulSax · Answer

Break down the argument

The passage says:

1. Mammals remained small while dinosaurs dominated.
2. After dinosaurs became extinct, mammals grew dramatically larger.
3. One reason was that mammals no longer had to compete with herbivorous dinosaurs for space to roam & vegetation (food)
4. More food/resources allowed larger mammals to thrive.
5. This led to large mammals such as hippopotamuses and giraffes.

So the key causal relationship is:
 Less competition for resources → mammals could become much larger.

(A)If the dinosaurs had lived longer, mammals today would be much smaller yet still herbivorous.
 Too strong . The passage does not establish what mammals would be today, nor that they would necessarily remain herbivorous.
 Not must be true.

(B) If the hippopotamus we know today was 1,000 times smaller, other mammals would also be significantly smaller.
Nothing in the passage links the size of hippos to the  size  of all other mammals.
 Unsupported .

(C) If other larger nonmammals had survived the event that made the dinosaurs extinct, modern mammals may have been much smaller due to competition for resources.
This matches the logic perfectly:
Dinosaurs' disappearance  removed  competition.
If  another group of large nonmammals had remained and competed for the same resources , mammals may have stayed smaller.
Notice the careful wording " may have been," not "would have been ."
 Must be supported . That's your Answer

(D) If mammals had been larger during the time of the dinosaurs, the resulting competition would have made both extinct.
The passage never suggests competition causes extinction of both groups.
 Unsupported.

(E) If hippopotamuses and giraffes had evolved as carnivores ... large mammals most likely would not have competed with dinosaurs for space and food.
The passage only discusses herbivorous dinosaurs and competition for vegetation. It says nothing about carnivorous evolution of hippos or giraffes.
 Unsupported.

egmat · Answer

Hi Adit_,

Your instinct that "neither feels shell-tight" is actually the right radar - this is a  must be true  question, so the test is whether the passage  forces  the statement, not whether it leaves it possible. Two small reads are doing the damage here. Let's pull them apart.

The causal claim in the passage - read it precisely

The passage gives you exactly one cause-and-effect rule:

-  Competition for space and food with large competitors  → mammals stay small.
- Remove the competitors (dinosaurs go extinct) → mammals grow.

That's the only mechanism on the table. The hippo and giraffe are mentioned only as  examples  of what mammals became  after  the competitors disappeared - they aren't a rule about how mammals' sizes relate to each other.

Why B is not forced

B says: if today's hippo were  1,000 times smaller ,  other  mammals would also be significantly smaller.

This needs a link the passage never gives - a correlation  among mammals  themselves. The passage tells you what made mammals grow (no competitors), not that mammal sizes move together. A smaller hippo in some alternate world could exist for any number of reasons - none of them say anything about giraffes or other mammals.

You spotted this yourself when you wrote  "there need not be such a correlation, but such a correlation could exist from the argument."  That's the giveaway:  could exist  is not  must be true . On a Deduction question,  could  loses.

Why C is forced - and the word "may" is doing real work

C says: if larger nonmammals had survived, modern mammals  may  have been much smaller due to competition for resources.

This is just the passage's own rule, run in reverse:

- Passage: large competitors gone → mammals grew large.
- C: large competitors stay → mammals  may  stay small.

That word  "may"  is exactly why C clears the bar that B fails. C isn't claiming mammals  definitely would  be smaller - only that this outcome is on the table because the very mechanism the passage names (competition for resources) is present. Since the passage explicitly says competition kept mammals small, "may have been smaller" is something the passage  forces  you to accept.

The habit to build - watch the modal words

Try this on the two choices and feel the difference:

- B says  "would be"  - a strong, definite claim. The passage has to support a guaranteed link, and it doesn't.
- C says  "may have been"  - a soft, possibility claim. The passage only has to leave room for it, and it actively does.

On  must be true  questions, the weaker the claim's wording ( may ,  could ,  some ), the easier it is for the passage to force it. The stronger the wording ( would ,  will ,  all ), the more the passage has to deliver. B over-promises; C under-promises just enough to be airtight.

Answer: C

During the first 140 million years of existence on earth, mammals were

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During the first 140 million years of existence on earth, mammals were

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