Paleontologist: The giant pterosaur Quetzalcoatlus had an eleven

Question

Paleontologist: The giant pterosaur  Quetzalcoatlus  had an eleven-meter wingspan and was too heavy to take off merely by flapping its wings, even with a running start. One biomechanics researcher found that  Quetzalcoatlus  had wings that were far sturdier than it would have needed during flight, and concluded that it took off by using the wings as forelimbs, beginning its flight by leaping with all four "legs." However, this hypothesis is implausible, since  Quetzalcoatlus  had to attain a speed of at least forty-eight kilometers per hour to take off, which would have been impossible from a standing jump.

Of the following, which, if true, would be the most effective rebuttal the biomechanics researcher could make to the paleontologist's argument?

A)  Quetzalcoatlus  could plausibly have taken off by diving off a cliff from its hind limbs, then using the fall to accelerate.
B) Most other pterosaur species are known to have taken off by flapping their wings after a running start.
C) The sturdy forelimbs of  Quetzalcoatlus  could have helped it to subdue its prey when not in flight.
D)  Quetzalcoatlus  could plausibly have run fast enough to take off by leaping into the air after a running start.
E) Researchers know of no plausible way in which any giant pterosaur species could have attained a speed of 48 kilometers per hour before taking off.

gmatophobia · Accepted Answer

Conclusion of the argument  : The hypothesis that Quetzalcoatlus took off by using the wings as forelimbs, beginning its flight by leaping with all four "legs." is implausible.
  Support Given:    Quetzalcoatlus  had to attain a speed of at least forty-eight kilometers per hour to take off, which would have been impossible from a standing jump.
Hence the Paleontologist assumes that a standing jump is the only way to attain a speed of at least forty-eight kilometers per hour that the giant pterosaur  Quetzalcoatlus  could have employed. 
Any option that challenges this assumption can weaken the argument. 
   Answer Choice Elimination    
 A)  Quetzalcoatlus  could plausibly have taken off by diving off a cliff from its hind limbs, then using the fall to accelerate. 
While this option provides an alternate way of attaining speed, however, this method doesn't address the Paleontologist's argument. The Paleontologist refutes the researcher's finding, that it took off by using the wings as forelimbs, beginning its  flight by leaping with all four "legs."  because the Paleontologist believes that  Quetzalcoatlus  had to attain a speed of at least forty-eight kilometers per hour to take off, which would have been impossible from a standing jump. The option provides an alternate explanation of how the  Quetzalcoatlus  could have taken off, but doesn't address why it couldn't have leaped with all four legs. Hence, the option doesn't weaken the argument. 
 B) Most other pterosaur species are known to have taken off by flapping their wings after a running start. 
This information about other pterosaur species doesn't directly challenge the biomechanics of Quetzalcoatlus itself. Hence, we can eliminate option B.
 C) The sturdy forelimbs of  Quetzalcoatlus  could have helped it to subdue its prey when not in flight. 
This option is out of scope. What other uses the  Quetzalcoatlus  had of its forelimbs is not the contention of this argument. 
 D)  Quetzalcoatlus  could plausibly have run fast enough to take off by leaping into the air after a running start. 
This counters the paleontologist's argument that it would have been impossible for Quetzalcoatlus to attain the necessary speed for takeoff from a  standing jump . The option provides an alternate way the  Quetzalcoatlus  could have attained the speed. If Quetzalcoatlus could achieve the required speed by  running  before taking off, then the conclusion of the author becomes less compelling.
 E) Researchers know of no plausible way in which any giant pterosaur species could have attained a speed of 48 kilometers per hour before taking off. 
This sort of strengthens the argument. The option eliminates any possible way that any giant pterosaur species could have attained a speed of 48 kilometers per hour before taking off. Hence, it makes us believe more that the conclusion that the author has made is indeed true. 
  Option C

Fish181 · Answer

Answer choice A is what a lot of people chose but it can't be A due to the fact that the passage says the dinosaur leaps from all four "legs". If it dives off of something on its hind legs then it's not leaping with all four legs.

However, D still allows this fact to be true. In your head picture some winged dinosaur running on all fours and then jumping from all fours into the air.

Weird question but the answer is definitely D.

sachi-in · Answer

There are two ways to focus on the passage:   1.  Static Jump    vs   2.  Flight

Static jump:_________

P:      Quetzalcoatlus needs 48+ kmph to take off   , not possible from a standing jump

To prove Paleontologist(P) wrong Biomed researcher (BR) must provide an edivience that suggests :     Quetzalcoatlus needs 48+ kmph to take off,    possible from a standing jump .

But if BR says:    Quetzalcoatlus needs 48+ kmph to take off,   possible by a combination of running + leaping (  option D  ) 
  this suggests:    Quetzalcoatlus needs 48+ kmph to take off,   possible by a combination of running + leaping (  P is right  it's not possible from standing jump )

But this doesnot counter  P's  statement that  Quetzalcoatlus can't take off just by jumping

To simply disprove / provide rebuttal to A we must say:     Quetzalcoatlus needs 48+ kmph to take off,    possible from a standing jump ( by jumping off from a cliff  - option A )

Option A is correct as far as this line of reasoning is concerned

Flight:____________

The   BR   actually concludes that "  Quetzalcoatlus could fly  ", (wheather a static jump was involved or not is not the important aspect, it's an evidence in support). And the focus of   P's   argument is   they can't fly   ( by disproving that static jump can't give 48+ kmp speed ). But   P   overlooks the fact that   flight is possible   by a combination of (run + jump).

If the focus is on flight then   Quetzalcoatlus can fly anytime they wish to, if they can take off by running and jumping, this provides additional evidence in support of flight ( option D ) 
 But
If they need a cliff to jump off and fly, flight is dependent on Cliff, so that's could be called gliding ( option A )

If we reread the passage we will observe the subtle difference in the focus (on flight) , hence   option D   is the correct choice.

yogi.0195 · Answer

Weird question indeed! But wouldn't D imply that the pterosaur ran using all four legs to be in a position to be on its fours just before leaping or could we assume that it's running using two but just before it's about to leap, it falls on its four and leaps with all four? Sounds weird and seems weird all along!

Fish181 · Answer

Yea possibly... I think the key takeaway here is that when you're stuck between A and D, answer choice A says the creature dives off its hind legs which are not all four of its legs therefore you'd eliminate A and that just leaves D as your answer.

I wonder whether hindlegs is something a nonnative English speaker would usually understand or not. It's a weird term.

tuyaras · Answer

I didn't choose D. as the passage said "However, this hypothesis is implausible, since Quetzalcoatlus had to attain a speed of at least forty-eight kilometers per hour to take off," and choice D. is just the  direct opposite  of what the passage say which is very strange to choose.

Raman109 · Answer

Paleontologist: The giant pterosaur Quetzalcoatlus had an eleven-meter wingspan and was too heavy to take off merely by flapping its wings, even with a running start. One biomechanics researcher found that Quetzalcoatlus had wings that were far sturdier than it would have needed during flight, and concluded that it took off by using the wings as forelimbs, beginning its flight by leaping with all four "legs." However, this hypothesis is implausible, since Quetzalcoatlus had to attain a speed of at least forty-eight kilometers per hour to take off, which would have been impossible from a standing jump.

Of the following, which, if true, would be the most effective rebuttal the biomechanics researcher could make to the paleontologist's argument?

A) Quetzalcoatlus could plausibly have taken off by diving off a cliff from its hind limbs, then using the fall to accelerate. - provides a new hypothesis rather than a rebuttal.

B) Most other pterosaur species are known to have taken off by flapping their wings after a running start. - "other pterosaur species" are out of scope.

C) The sturdy forelimbs of Quetzalcoatlus could have helped it to subdue its prey when not in flight. - out of scope.

D) Quetzalcoatlus could plausibly have run fast enough to take off by leaping into the air after a running start. - Yes. This means that the "giant pterosaur" still uses the same mechanism that the "biomechanics researcher" recommended - it took off by using the wings as forelimbs, beginning its flight by leaping with all four "legs." The "Paleontologist" assumes there is no other way by mentioning that it is "impossible from a standing jump." But this option highlights that a "giant pterosaur" could gain speed and then use limbs to leap into the air.

E) Researchers know of no plausible way in which any giant pterosaur species could have attained a speed of 48 kilometers per hour before taking off. - Weakner at best for biomechanics researcher.

DmitryFarber · Answer

Well, we do want to oppose the argument. You're right that we don't usually do that by directly contradicting one of the author's premises. However, D doesn't do that. The original argument says that the leaping hypothesis is implausible because the dino couldn't achieve the needed speed for flight from a standing jump. D just points out that it *could* achieve that speed with a *running* jump. That's a different possibility that the author didn't address, so it effectively weakens the argument.

kymoll373 · Answer

I feel that everyone's response completely disregards the statement in the premise that clearly says the pterosaur "was too heavy to take off merely by flapping its wings, even with a running start". I was between A & D during my mock and went with A b/c D suggests the pterosaur would be able to fly from a running start which seemingly attacks a premise in the first sentence that  I thought  we are supposed to be taking as true. Can anyone help me understand where my logic is flawed?

KarishmaB · Answer

Paleontologist : Q had wings too heavy to take off merely by  flapping its wings, even with a running start .

Biomechanics researche r:Q had wings that were far sturdier than it would have needed during flight. So it took off by using the wings as forelimbs,  beginning its flight by leaping with all four "legs."  (not by merely flapping its wings)

Paleontologist : This hypothesis is implausible, since  Q  had to attain a speed of 48 kmph to take off, which would have been  impossible from a standing jump .

What could the  Biomechanics researcher  say now? He could say that Q could attain the speed by  leaping after a running start  (not from a standing jump)

This is option (D) hence it works. 
  D)  Quetzalcoatlus  could plausibly have run fast enough to take off by leaping into the air after a running start.

Why is (A) incorrect.

A)  Quetzalcoatlus  could plausibly have taken off by diving off a cliff from its hind limbs, then using the fall to accelerate.

Biomechanics researcher is rooting for  beginning its flight by leaping with all four "legs." 
Option (A) talks about using only hind legs. That is not consistent with Biomechanics researcher's theory.

Answer (D)

egmat · Answer

Understanding the Rebuttal Structure in This CR Question 
This question presents a fascinating argument structure that appears frequently on the GMAT. Let me break down the logical flow to help you see the pattern:

The Argument Chain: 
 
 Paleontologist presents background: Quetzalcoatlus too heavy for normal wing-flapping takeoff 
 Biomechanics researcher's hypothesis: Used sturdy wings as forelimbs for four-legged jumping takeoff 
 Paleontologist's criticism: This is impossible because 48 km/h speed needed, can't achieve from  standing jump

Key Strategic Insight: 
The paleontologist's entire criticism rests on one assumption - that the four-legged jump would be from a  standing position . This is the vulnerability we need to exploit for an effective rebuttal.

Let's analyze the trap answers first:

Option A: Cliff diving approach  - This abandons the researcher's hypothesis entirely rather than defending it. Classic trap!
 Option C: Alternative use for sturdy wings  - Actually  undermines  the researcher by suggesting wings had different purpose
 Option E: No pterosaur could reach 48 km/h  - This  strengthens  the paleontologist's argument!

The Correct Approach:

We need something that shows the four-legged jumping method  could  achieve 48 km/h

Want to see why (D) perfectly addresses the speed criticism and learn the complete framework for handling rebuttal questions?

The  detailed solution  reveals a powerful pattern recognition technique that applies to all CR rebuttal questions, plus shows you exactly how to spot the "assumption vulnerability" that makes these questions solvable in under 90 seconds.

Paleontologist: The giant pterosaur Quetzalcoatlus had an eleven

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­Paleontologist: The giant pterosaur Quetzalcoatlus had an eleven

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615 to 715 in 15 Days (Ria's Strategies)

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Paleontologist: The giant pterosaur Quetzalcoatlus had an eleven