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# Birds have been said to be descended from certain birdlike dinosaur sp

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Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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Updated on: 15 May 2018, 09:45
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Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils that are much older than the earliest birdlike dinosaur fossils that have been found.

Which of the following is an assumption on which the argument relies?

A. The birdlike dinosaurs have no living descendants.

B. There are no flightless dinosaur species that have the distinctive structural features shared by birds and birdlike dinosaurs.

C. There are no birdlike dinosaur fossils that are older than the bird fossils but have not yet been unearthed.

D. It could not have been the case that some birds were descended from one of the birdlike dinosaur species and other birds from another.

E. Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features.

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Sentence Correction-Collection of Ron Purewal's "elliptical construction/analogies" for SC Challenges

Originally posted by AbdurRakib on 15 Jun 2016, 12:57.
Last edited by Bunuel on 15 May 2018, 09:45, edited 1 time in total.
Edited the question.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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16 Jun 2016, 04:08
C most logically fits the bill...

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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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18 Jun 2016, 02:21
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Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils much older than the earliest birdlike dinosaur fossils that have been found.

Pre- thinking - Because birdlike dinosaur fossils that are older that the bird fossils have not been found , it does not mean such birdlike dinosaur did not exist before birds .

Which of the following is an assumption on which the argument relies?

A) The birdlike dinosaurs have no descendants. Out of scope
B) There are no flightless dinosaur species that have the distinctive structural features shred by birds and birdlike dinosaurs. Out of scope
C) There are no birdlike dinosaur fossils that are older that the bird fossils but have not yet been unearthed. Correct - if we negate this statement , then the argument falls apart .
D) It could not have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another. Incorrect
E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features. Incorrect

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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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24 Jun 2016, 06:46
Using Negation
C) There are birdlike dinosaur fossils that are older that the bird fossils but have not yet been unearthed -- The argument will fall apart

So the correct answer is C
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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26 Jun 2016, 07:04
The issue with the reasoning is the assumption that there are no birdlike dinosaurs fossils that have not been found.

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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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14 Aug 2016, 16:06
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Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils much older than the earliest birdlike dinosaur fossils that have been found.

Which of the following is an assumption on which the argument relies?

PRETHINKING: DINOSAUR CAME LATER TO THOSE BIRDS WHOSE FOSSILS ARE DATED OLDER THAN THE DINOSAUR FOSSILS.

A) The birdlike dinosaurs have no descendants.
B) There are no flightless dinosaur species that have the distinctive structural features shared by birds and birdlike dinosaurs.
C) There are no birdlike dinosaur fossils that are older that the bird fossils but have not yet been unearthed.
This is one of the versions of our PRETHINKING.
D) It could not have been the case that some birds were descendant from one of the bird-like dinosaur species and other birds from another.
E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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04 Oct 2016, 02:42

It clearly states that there are no birdlike dinosaur fossils that are older that the bird fossils because which conclusion will hold true.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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15 Oct 2016, 08:54
Was able to narrow it down to C and E. Then used negation test to zero in on C. The negation test breaks down the argument completely.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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23 Jan 2017, 03:09
My reasoning:
Conclusion: Birds cannot be descendant of certain birdlike dinosaur species with which they share distinctive structural features
Trying to negate the D:
It could have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another --> ruining the conclusion
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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23 Jan 2017, 07:12
It is the assumed that there are no birdlike dinosaurs fossils that have not been found yet.

Therefore C is correct.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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25 Jan 2017, 14:11
C is the answer. If it is not true, there is a possibility that undermine the argument.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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27 Feb 2017, 14:41
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Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils much older than the earliest birdlike dinosaur fossils that have been found.

Which of the following is an assumption on which the argument relies?

A) The birdlike dinosaurs have no descendants.
B) There are no flightless dinosaur species that have the distinctive structural features shred by birds and birdlike dinosaurs.
C) There are no birdlike dinosaur fossils that are older that the bird fossils but have nit yet been unearthed.
D) It could not have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another.
E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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27 Feb 2017, 18:33
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Simplify the argument -

Bird fossils much older than birdlike dinosaur fossils have been found --> Birds did not descend from certain birdlike dinosaur fossils

Let us look at the answer options -

Option A - Incorrect.
Try to negate this. Even if there were descendants of birdlike dinosaurs, the argument still holds because bird fossils much older than them have been found.

Option B - Incorrect.
We are interested only in birds and birdlike dinosaurs and their fossils. Talking about flightless dinosaurs is not relevant to the argument.

Option C - Correct.
Negate this.
If there are indeed such fossils (but have not yet been unearthed), the conclusion "Birds did not descend from certain birdlike dinosaur fossils" will be significantly weakened.

Option D - Incorrect.
Even if that were the case, the argument is not weakened because bird fossils that are much older than those of birdlike dinosaurs have been found.

Option E - Incorrect.
Negate this one.
"Birds could have descended from dinosaur species with which the birds do not share the distinctive structural features." - But we do not know whether these other dinosaur species lived before or after birdlike dinosaurs.
If they did not live before, the argument is not weakened. Hence, incorrect.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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28 Feb 2017, 11:35
p1 : Birds descended bird like dinosaur species with which they share distinctive structural features

conclusion this cannot be true why because bird fossils much older

what if dinosaur fossils found are older than bird fossils. Conclulsion be false
hence assumption be :- dinosaur fossils found are not older than bird fossils
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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11 Apr 2017, 20:34
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AbdurRakib wrote:
Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils much older than the earliest birdlike dinosaur fossils that have been found.

Which of the following is an assumption on which the argument relies?

A) The birdlike dinosaurs have no descendants.
B) There are no flightless dinosaur species that have the distinctive structural features shred by birds and birdlike dinosaurs.
C) There are no birdlike dinosaur fossils that are older that the bird fossils but have nit yet been unearthed.
D) It could not have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another.
E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features.

OG 2017 (Book Question 607)

nit (noun) = the egg of a louse, which sticks to the fur of an animal or the hair of a person

Birds and Dinosaurs

Step 1: Identify the Question

The word assumption in the question stem indicates that this is a Find the Assumption question.

Step 2: Deconstruct the Argument

Birds desc from B-like dinos?
C: Fossil = NO b/c B fossils older than B-like dino fossils

The author concludes that a certain theory CANNOT be true. As evidence, the author states that there are bird fossils even older than the oldest birdlike dinosaur fossils found. So birds must be descended from something other than birdlike dinosaurs?

NOT necessarily. The author is assuming that the fact that older birdlike dinosaur fossils haven’t been found means that these fossils don’t exist. It’s possible that there were older birdlike dinosaurs but either their fossils haven’t been found yet or their bones didn’t survive as fossils for some reason.

Step 3: Pause and State the Goal

On Assumption questions, the goal is to find something that the author must believe TO BE TRUE in order to draw the conclusion.

Step 4: Work from Wrong to Right

(A) The author’s argument does not assume anything about modern-day descendants of the birdlike dinosaurs.
(B) The argument is confined to the possible connection between birds and birdlike dinosaurs. Flightless dinosaurs, another category, are not at issue in the argument.
(C) CORRECT. The author does assume that there aren’t older fossils of the birdlike dinosaurs that just haven’t been found yet. Try the Negation Test: if there are birdlike dinosaur fossils that just HAVEN'T been found yet, then the author’s argument is ruined.
(D) The author’s argument does not assume that all birds descended from the same birdlike dinosaur species. The author’s argument is open to the idea that there could have been multiple birdlike dinosaur species from which modern-day birds evolved.
(E) The argument is confined to rebutting the idea that birds descended from certain birdlike dinosaur species. It does not address whether the birds could have been descended from other dinosaur species with different structural features.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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28 Sep 2017, 04:10
Hientran48 wrote:
My reasoning:
Conclusion: Birds cannot be descendant of certain birdlike dinosaur species with which they share distinctive structural features
Trying to negate the D:
It could have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another --> ruining the conclusion

I negated D and it destroyed the conclusion for me too. Though option C's negation was a stronger destroyer of the argument, I request an expert to clarify why option D is certainly not the right answer.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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28 Sep 2017, 04:11
I negated D and it destroyed the conclusion for me. Though option C's negation was a stronger destroyer of the argument, I request an expert to explain why option D is certainly not the right answer.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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29 Sep 2017, 15:43
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gumnamibaba wrote:
I negated D and it destroyed the conclusion for me. Though option C's negation was a stronger destroyer of the argument, I request an expert to explain why option D is certainly not the right answer.

Quote:
D) It could not have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another.

To negate choice (D) is not to say that some birds definitely were descended from multiple dinosaur species. If we do not make the assumption stated in choice (D), we allow for the possibility that some birds were descended from MULTIPLE dinosaur species rather than a single birdlike dinosaur species.

In order for the author's argument to hold, it is not necessary that we first establish that birds could not have descended from multiple dinosaur species. Here is a breakdown of the argument if we do not make the assumption stated in choice (D):

• Birds may have descended from one or more species of dinosaurs
• Whether it was one species or multiple species, if birds were in fact descended from dinosaurs, we would not expect to find birds fossils that are older than dinosaur fossils.
• Since there are bird fossils that are much older than the earliest birdlike dinosaur fossils that have been found, the fossil record shows that birds could NOT have descended from certain birdlike dinosaur species.

Choice (D) is tricky, but, unlike choice (C), it is not a required assumption.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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18 Oct 2017, 07:47
AbdurRakib wrote:
Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils much older than the earliest birdlike dinosaur fossils that have been found.

Which of the following is an assumption on which the argument relies?

A) The birdlike dinosaurs have no descendants.
B) There are no flightless dinosaur species that have the distinctive structural features shred by birds and birdlike dinosaurs.
C) There are no birdlike dinosaur fossils that are older that the bird fossils but have nit yet been unearthed.
D) It could not have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another.
E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features.

OG 2017 New Question

Hello, below is my analysis.

- Before, bird is believed come from birdlike dinosaurs, not from bird itself.
- However, this might be wrong, because we found BIRD FOSSIL that is OLDER than BIRDLIKE DINOSAUR FOSSIL.

- So, let's say that the age of BIRD FOSSIL is year 100 and the age of BIRDLIKE DINOSAUR FOSSIL is from year 200.

- Is it enough to conclude that the descendant of the BIRD is not A BIRDLIKE DINOSAUR?
- How if one day we found another BIRDLIKE DINOSAUR FOSSIL from year 50? --> This might be our assumption.

- Clearly C state this assumption. It must be true to the conclusion hold true.
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Re: Birds have been said to be descended from certain birdlike dinosaur sp [#permalink]

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06 Dec 2017, 03:04
AbdurRakib wrote:
Birds have been said to be descended from certain birdlike dinosaur species with which they share distinctive structural features. The fossil record, however, shows that this cannot be so, since there are bird fossils much older than the earliest birdlike dinosaur fossils that have been found.

Which of the following is an assumption on which the argument relies?

A) The birdlike dinosaurs have no descendants.
B) There are no flightless dinosaur species that have the distinctive structural features shred by birds and birdlike dinosaurs.
C) There are no birdlike dinosaur fossils that are older that the bird fossils but have nit yet been unearthed.
D) It could not have been the case that some birds were descendant from one of the bird like dinosaur species and other birds from another.
E) Birds cannot have been descended from dinosaur species with which the birds do not share the distinctive structural features.

OG 2017 New Question

Pre thinking can really help you with this sort of questions, read the premise and then conclusion. Now think this way, okay the conclusion is (since there are bird fossils much older than the earliest birdlike dinosaur fossils that have been found.)
What can be the reason which negates this. maybe all fossils of birdlike dinosaurs have not been found??.

And you will notice it is the option C

Its not always that what you pre think will be among the options but it gives you the idea of what lines to follow on. Powerfull tool to have for CR.
Re: Birds have been said to be descended from certain birdlike dinosaur sp   [#permalink] 06 Dec 2017, 03:04

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