#6 - Recently discovered bird fossils are about 20 million

[Administrator]

Complete Question Explanation

Flaw in the Reasoning. The correct answer choice is (A)

This stimulus deals with recently discovered bird fossils that are 20 million years older than the
fossils of some birdlike dinosaurs. Most paleontologists claim that birds descended from these
birdlike dinosaurs. But the author of this stimulus concludes that no birds could have descended from
any dinosaur.

The question stem asks how the reasoning is fl awed. What is wrong with the conclusion above?
The author concludes that birds did not descend from any dinosaur because some bird fossils are
older than the fossils of some dinosaurs from which the birds are believed to have descended. The
argument breaks down as follows:

• Premise: There are some bird fossils older than some dinosaur fossils.
  Conclusion: Therefore, no bird could have descended from any dinosaur.

This conclusion is overly broad, and is not justifi ed based on the information provided in the
stimulus (for example, hypothetically, birds could have descended from dinosaurs with the two
species coexisting for 50 million years. If this were the case, we could conceivably find some of the
older bird fossils to be 20 million years older than some recent dinosaur fossils, even though the
birds in this hypothetical scenario descended from the dinosaurs).

Answer choice (A): This is the correct answer choice. The author draws a generalization that is
broader than warranted by the findings cited. In other words, the premise that there are some bird
fossils that are older than some dinosaur fossils is not sufficient to draw such a broad conclusion
about birds and dinosaurs in general, as discussed above.

Answer choice (B): While the author of this stimulus does indeed reject a consensus view, there is
not necessarily a requirement to provide a counterexample when doing so. Since this is not a fl aw,
this answer choice should be rejected.

Answer choice (C): This answer choice describes the classic source argument, or ad hominem attack.
The author of the stimulus does not personally attack the paleontologists who hold the majority
opinion, so this answer choice is incorrect.

Answer choice (D): Since the argument in the stimulus concerns whether or not any bird descended
from any dinosaur, the possibility referenced in this answer choice is irrelevant. Since this possibility
need not be considered, this answer choice cannot be correct.

Answer choice (E): The argument does not explicitly discuss the possibility that the two species
discussed share a common ancestor, but this is irrelevant to the author’s conclusion that no bird
descended from any dinosaur, and that the prevailing paleontologist view is wrong.

[netherlands]

Hi there PS,

I can understand why A is correct - the author makes the assumption that because birds don't descend from birdlike dinosaurs then they must not descend from any dinosaurs. I guess that simply because we have findings going against the idea that birdlike dinosaurs are the ancestor doesn't mean that we can say they didn't descend from any other dinosaurs. So the author is making a general statement ( encompassing all dinosaurs) based off of limited findings ( birdlike dinosaur fossils being younger).

But again, I find myself looking at another possible choice, E, and wondering why that too couldn't be considered a flaw. Doesn't the author assume that the birds didn't descend from another dinosaur (common ancestor) that the birdlike dinosaur also descended from. Maybe "A" kind of encompasses that answer choice though.

[BethRibet]

Hi Netherlands,

Thanks for writing in. Answer choice E reads: "ignores the possibility that dinosaurs and birds descended from a common ancestor"

So it's certainly true that the passage does not acknowledge the possibility that birds and dinosaurs share a common ancestor. I understand your argument/interpretation of E, but the phrasing dinosaurs, plural, seems to indicate all dinosaurs, not just one breed of dinosaur (birdlike or not) which might be descended from a different breed of dinosaur. Given that, I would rule out D.

Hope that helps!

Beth

[MBG13]

I want to make sure that I understand because I also selected E. The reason that this answer is wrong is that its saying dinosaurs (plural) in general instead of "birdlike dinosaurs." Am I understanding that correctly?

[Shannon Parker]

Hi there,

I can understand why answer choice "E" is an attractive answer because it is disregarded in the stimulus. However answer choice "E" has no bearing on the argument in this question. Whether or not birds and dinosaurs descended from a common ancestor does not affect whether any bird descended from any dinosaur. The common ancestor could have been a bird, or some other species.

The flaw in this argument is a simple over generalization, where the author draws the conclusion that no bird descended from any dinosaur bases solely on proof that one species of bird is not descendent from the species of dinosaur that it was previously thought to have descended from. There are numerous other species of birds that could have descended from dinosaurs, and the stimulus does not cutoff the possibility that these birds descended from a different dinosaur.

Answer choice "A" is therefore the correct answer.

I hope this helps.

~Shannon

[Aliya316]

Here I feel like the author is making a narrow definition, that’s why I chose E. In my mind, the author separated birdS from any dinosaur origin.

[lsatstudying11]

Hello!

Initially, when I read the stimulus, I thought to myself that one problem might be there could exist fossils even older than 20 million years that have not yet been discovered but would demonstrate that birds did come from dinosaurs. Could this hypothetically be a correct answer? Or is this off the mark of the conclusion or something that goes against what is stated to be 'generally accepted'? Thank you

[Adam Tyson]

The author's failure to consider that possibility is why the conclusion is too broad, lsatstudying11, so yes, that is at least part of the flaw here. So is failing to consider that while some birds might be older than dinosaurs, other birds may nonetheless have descended from dinosaurs. There are possible alternatives that the argument failed to consider!

And Aliya, the problem with answer E is that if the author HAD considered a common ancestor, that would actually STRENGTHEN their argument! That would be further evidence that birds did not descend from dinosaurs! So while the author never did mention that possibility, that's not a flaw in this case.