Dinosaur expert: Some paleontologists have claimed that birds are desc

Question

Dinosaur expert: Some paleontologists have claimed that birds are descendants of a group of dinosaurs called dromeosaurs. They appeal to the fossil record, which indicates that dromeosaurs have characteristics more similar to birds than do most dinosaurs. But there is a fatal flaw in their argument; the earliest bird fossils that have been discovered date back tens of millions of years farther than the oldest known dromeosaur fossils. Thus the paleontologists' claim is false'.

The expert's argument depends on assuming which one of the following?

(A) Having similar characteristics is not a sign that types of animals are evolutionarily related.

(B) Dromeosaurs and birds could have common ancestors .

(C) Knowledge of dromeosaur fossils and the earliest bird fossils is complete.

(D) Known fossils indicate the relative dates of origin of birds and dromeosaurs.

(E) Dromeosaurs are dissimilar to birds in many significant ways.

rf3d3r3r · Accepted Answer

Here was my thought process for the question: Stem lists assumption, so look for SUPPORTER or DEFENDER assumptions based on the stimulus. Stimulus notes: The expert argues that the paleontologists are wrong in their claim that dromeosaurs are similar to birds BECAUSE the bird fossils are much much older than dromeosaur fossils. A big gap in the expert's thinking, therefore, is that he/she is thinking that the time gap is the reason for the paleontologists flaw in reasoning. This was the major gap that popped out on my first reading of the stimulus. A - This assumption is not the crux of the expert's counterargument to the paleontologists. Nothing in the stimulus suggests that the expert disagrees with the similarity of characteristics. B - The expert is actually assuming the OPPOSITE of this answer. The paleontologists are making this assumption. Remember, there are two different viewpoints in this question. C - At first glance this might make sense - all the fossils have been collected and the expert can now draw his conclusion. However, try negating this answer choice. Knowledge of dromeosaur fossils and the earliest bird fossils is NOT complete. This does not weaken the expert's conclusion severely. At this point, though, you could hold on to this answer choice as a contender. D - This is correct - The argument refers to fossils that have been found, and that the time difference between the fossils can somehow invalidate the relationship between birds and dromeosaurs. As a test, try negating it: Known fossils DO NOT indicate the relative dates of origin of birds and dromeosaurs. The expert would not be able to substantiate his/her claim now; if fossils didn't indicate the dates of their existence, then the paleontologists theories could not be disputed. E - The expert doesn't assume or attack the paleontologists claim of differences in the species, just the time difference of the fossils. --- My GMAT Experience: 670-to-760-q49-v44-ir-8-awa-6-0-no-stone-unturned-for-8-months-200051.html

Divyadisha · Answer

Can anyone please help me with this CR.

I chose 'A' as my answer because paleontologists reached to the conclusion, based on fossil record, that B and D are related after finding similar characteristic in them.

Dinosaur expert disagree with paleontologist.

Can't 'A' by the assumption that similar characteristics doesn't mean B and D are evolutionary related. Even if we negate the statement, it breaks down expert's conclusion.

I did'nt get why 'D' is the answer. What is the fossils have relative dates of origin? Does that mean B and D can't be related? Nothing in support of this is present in the argument.

Abhishek009 · Answer

Lets try -

Dinosaur expert's claim that birs are descendants of a group of dinosaurs called dromeosaurs is proved by -

But the flaw with the reasoning of the Dinosaur expert is -
 
  Bird fossils  =====tens of millions of years====== dromeosaur fossils.

If Bird  fossils > dromeosaur  fossils { Bird fossils existed before fossils of dromeosaur fossils } then the argument put forward by the Dinosaur expert is flawed.

Our argument here completely relies on the fossils of birds vs dromeosaur.

Now go through options (A) and (D) { Not going through all the options }

(A) Having similar characteristics is not a sign that types of animals are evolutionary related.

The stimulus presented to us talks about the fossil record to prove that the Dinosaur expert's reasoning is fasle. The author proves the fact by the use of the relative dates of origin of birds and dromeosaurs fossils in support of his reasoning.

Similar characteristics may be a sign of evolutaionary impact of birds/dromeosaurs but may we can not be 100% certain about it because the author uses scientific methods { dating fossils of birds and dromeosaurs }

(D) Known fossils indicate the relative dates of origin of birds and dromeosaurs.
 
Try to negate this option.

Known fossils do not indicate the relative dates of origin of birds and dromeosaurs.

If fossil records do not indicate the relative dates of origin of birds and dromeosaurs then the argument put forward by the author falls apart.
  
Hence IMHO (D)

Divyadisha · Answer

Loved the detailed explanation, and I really appreciate this effort.

However, one more query on the statement- 'earliest bird fossils that have been discovered date back tens of millions of years farther than the oldest known dromeosaur fossils.' - is that isn't it states the difference between the time of discovery of these fossils? Now the possibility is that bird's fossils were discovered first (tens of millions of year before D's fossils) or dremosaur's fossils were discovered first (bird's fossils were discovered tens of millions of year after D's fossil). The statement doesn't tell us that which fossil was discovered first.

Is there any gap in my understanding?

Abhishek009 · Answer

Ok lets try it again ( with a different approach as well )

The main point here is

The underlined part : date back tens of millions of years farther than the oldest known dromeosaur fossils.

I get 2 interpretations (about the time of discovery of the fossils)-

1. Bird fossils> dromeosaur fossils  - {  Bird fossils were discovered prior to discovery of dromeosaur fossils  }
 2. dromeosaur fossils> Bird fossils  - {  dromeosaur fossils were discovered prior to discovery of Bird fossils }

Further we have a very crucial piece of information presented in the stimulus -

The above sentence states that the time of discovery of the fossils ( Whether Bird fossils were discovered first or dromeosaur fossils ) is not important to us , the stimulus clearly states that in the time line of the fossils Bird fossils precceds dromeosaur fossils.

Elucidating further -

Say Bird fossils ( Dated to be 10,000 year old ) were discovered in the year 2000 , but dromeosaur fossils ( Dated to be 6,000 year old )were discovered in 1987. 
Though dromeosaur fossils were discovered prior to the discovery of the Bird fossils, it is the bird fossils that existed prior to dromeosaur fossils.

Thats my understanding from the stimulus, I guess this questions needs further discussion....

goforgmat · Answer

Can you please explain how you eliminated C?
I picked C because if the knowledge of the fossils is not complete there is a possibility that there are fossils that can substantiate Paleontologists claim .

Shiv2016 · Answer

Premise: Some paleontologists have claimed that birds are descendants of a group of dinosaurs called dromeosaurs. 
Premise: They appeal to the fossil record, which indicates that dromeosaurs have characteristics more similar to birds than do most dinosaurs. 
Premise: But there is a fatal flaw in their argument; the earliest bird fossils that have been discovered date back tens of millions of years farther than the oldest known dromeosaur fossils. 
Conclusion: Thus the paleontologists' claim is false'.

DROMEOSAURS--------------------BIRDS 
SAME CHARACTERISTICS………………….. 
This is not true……………………………….. BECAUSE BIRDS FOSSILS OLDER THAN DROMEOSAURS 
According to the argument, now Dromeosaurs become descendants of birds. 
The data on fossils is correct and there is no error.
(A) Having similar characteristics is not a sign that types of animals are evolutionarily related.
Incorrect. Negated statement supports the argument.

(B) Dromeosaurs and birds could have common ancestors.

They could have but that is not the point of discussion in this argument. Incorrect.

(C) Knowledge of dromeosaur fossils and the earliest bird fossils is complete.
If the knowledge is not complete then the conclusion no longer makes sense.

(D) Known fossils indicate the relative dates of origin of birds and dromeosaurs.
We do not want to know the exact date to support the conclusion. Incorrect.

(E) Dromeosaurs are dissimilar to birds in many significant ways.
OUT OF SCOPE.

nazgull · Answer

Hi Expert,

The last posts in this thread have left the quetion still open to discussion and I request you to kindly provide a conclusive explanation. As per my understanding:

PREMISE: the earliest bird fossils that have been discovered date back tens of millions of years farther than the oldest known dromeosaur fossils. 
CONCLUSION: Thus the paleontologists' claim is false'.

Now option D is a restatement of the premise. IMHO I find C to be more relvant.

GDT · Answer

Can someone pls explain why C is not correct and how D is correct

C says that knowledge of fossils of d & earliest known fossils of birds is complete- which implies there is no scope of future discovery of fossils of the 2 that would reverse the concl

D says that known fossils tell us the relative dates of origin which is already given in stimulus

CrackverbalGMAT · Answer

Hi
 
This can also be interpreted in a different way. This could mean that the knowledge of  currently discovered fossils  is complete ie; no further information can be gleaned from the fossils that we already have. Please note that as per the answer option, what is complete is the  knowledge . This could refer to knowledge from all fossils or knowledge from currently available fossils. The option does not make this distinction clear. If this alternative explanation is taken, then fossils discovered in the future may yet reverse the conclusion. Overall, there is some doubt in this option.

Answer option (D) states: "Known fossils indicate the relative dates of origin of birds and dromeosaurs."

The stimulus actually tells us something different. The stimulus states: "...the earliest bird fossils that have been discovered date back tens of millions of years farther than the oldest known dromeosaur fossils". This is not the same as knowing the  origins  of birds and dromeosaurs. The stimulus merely tells us that the dates of the fossils of birds are older than the dates of the fossils of dromeosaurs. This is clearly only about the fossils that we currently have discovered. There may yet be undiscovered fossils of dromeosaurs which are older than the oldest known fossils of birds. Option (D) states the assumption that this is not the case.

Hope this helps.

Elite097 · Answer

Evaluating (C): "Knowledge of dromeosaur fossils and the earliest bird fossils is complete."
Why it seems tempting:
If our knowledge of the fossil record is incomplete, there could exist older dromeosaur fossils that haven't been discovered yet, invalidating the expert's argument. It seems plausible that the expert might assume the fossil record is complete to confidently state that dromeosaurs cannot be ancestors of birds.

Why it is incorrect:
The expert does not explicitly or implicitly assume that the fossil record is complete. The argument can still hold even if there are gaps in the fossil record, as long as the currently known fossils are sufficient to compare the relative timelines of birds and dromeosaurs. The expert's reasoning hinges on the relative dates provided by known fossils, not on the completeness of the fossil record.

Dinosaur expert: Some paleontologists have claimed that birds are desc

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Dinosaur expert: Some paleontologists have claimed that birds are desc

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