theropods

[vikram4689]

Although many lines of evidence indicate that birds evolved from ground-dwelling theropod dinosaurs, some scientists remain unconvinced. They argue that theropods appeared too late to have given rise to birds, noting that Archaeopteryx lithographica - the oldest known bird - appears in the fossil record about 150 million years ago, whereas the fossil remains of various nonavian maniraptor theropods - the closest known relatives of birds - date only to about 115 million years ago. But investigators have now uncovered bones that evidently belong to nonavian maniraptors dating to the time of Archaeopteryx. In any case, failure to find fossils of a predicted kind does not rule out their existence in an undiscovered deposit. Skeptics also argue that the fused clavicles (the "wishbone") of birds differ from the unfused clavicles of theropods. This objection was reasonable when only early theropod clavicles had been discovered, but fossilized theropod clavicles that look just like the wishbone of Archaeopteryx have now been unearthed. Finally, some scientists argue that the complex lungs of birds could not have evolved from theropod lungs, an assertion that cannot be supported or falsified at the moment, because no fossil lungs are preserved in the paleontological record.

Which of the following is mentioned in the passage as an argument made by scientists who are unconvinced that birds evolved from theropod dinosaurs?
(A)There are no known theropod dinosaur fossils dating from a period after the time of Archaeopteryx.
(B)There are no known theropod dinosaur fossils that indicate the structure of those dinosaurs' lungs.
(C)Theropod dinosaurs appear in the fossil record about 150 million years ago.
(D)Theropod dinosaurs did not have fused clavicles.
(E)Theropod dinosaurs had certain bones that look just like those of Archaeopteryx.

[anuprajan5]

The answer is D

(A)There are no known theropod dinosaur fossils dating from a period after the time of Archaeopteryx. - In fact they do argue that the theropods lived later than the Archaeopteryx
(B)There are no known theropod dinosaur fossils that indicate the structure of those dinosaurs' lungs. - They don't argue this. They argue that that the complex lungs of birds could not have evolved from theropod lungs
(C)Theropod dinosaurs appear in the fossil record about 150 million years ago. - This is a counter to their argument
D)Theropod dinosaurs did not have fused clavicles. - Evident from - Skeptics also argue that the fused clavicles (the "wishbone") of birds differ from the unfused clavicles of theropods
(E)Theropod dinosaurs had certain bones that look just like those of Archaeopteryx. - Counter argument

[vikram4689]

in the quoted line, where is it mentioned that "Theropod dinosaurs did not have fused clavicles". It only compares fused clavicles of birds with unfused clavicles of theropods

[anuprajan5]

Vikram,

Isn't the primary difference in that the theropods had fused clavicles as compared to those of birds. WHat's the OA?

REgards
Anup

[vikram4689]

Isn't the primary difference in that the theropods had fused clavicles as compared to those of birds. WHat's the OA?

OA is D but i didn't understand how did you get there. unfortunately, i could not understand your last comment as well.

[anuprajan5]

Hey Vikram,

This is an RC passage where there is a lot of assertions by scientists and counter evidence. How I tackled this was by following only the assertions of the scientists. (because the counter evidence will confuse you as you read through the answer choices).

As to my choice and the statement in question - Skeptics also argue that the fused clavicles (the "wishbone") of birds differ from the unfused clavicles of theropods

I think the confusion stems from the fact that you think that the fused clavicles of birdes differ from the unfused clavicles. But differ through what? bone density? porosity? etc... Since none of that is evident and in essence the primary difference is that 1 is fused and the other is unfused.
Hence my conclusion.

[vikram4689]

I read your last para repeatedly but could not understand what you meant. I am listing out some points below. Please reply whether i am following your line of thought.

I think the confusion stems from the fact that you think that the fused clavicles of birdes differ from the unfused clavicles. - from the underlined portion it seems that you were suggesting that bold portion is NOT true. is this what you meant. I am asking this because passage clearly states that FUSED clavi. of birds DIFFER from UNFUSED clavi. of theropods.

Also, from blue statement i can only infer that birds have FUSED clavi. and theropods have UNFUSED clavi. and that both of these clavi. differ. NOW, how did you find that theropods DON'T have UNFUSED clavi. From question it is clear that correct answer will be MENTIONED in passage and NOT inferred.

[anuprajan5]

I read your last para repeatedly but could not understand what you meant. I am listing out some points below. Please reply whether i am following your line of thought.

I think the confusion stems from the fact that you think that the fused clavicles of birdes differ from the unfused clavicles. - from the underlined portion it seems that you were suggesting that bold portion is NOT true. is this what you meant.

I am asking this because passage clearly states that FUSED clavi. of birds DIFFER from UNFUSED clavi. of theropods. Also, from this statement i can only infer that birds have FUSED clavi. and theropods have UNFUSED clavi. and that both of these clavi. differ. NOW, i how did you find that theropods DON'T have UNFUSED clavi. From question it is clear that correct answer will be MENTIONED in passage and NOT inferred.

The bold part is true. You seems to be getting something wrong. My answer and the option says that theropods do not have fused clavicles, which in essence means they have unfused clavicles. Nowhere do I mention that they don't have unfused clavicles. They don't have FUSED clavicles.

[vikram4689]

sorry for confusion. made a typo.

ok, we are in agrrement that
1)birds have FUSED clavi.
2)theropods have UNFUSED clavi.
3)that both of these clavi. in 1) and 2) differ.

now how did you find that theropods do not have FUSED clavi.

[anuprajan5]

Vikram,

This is not a factual question. This is a question whereby we are looking at the argument used by the scientists that are not convinced.

Which of the following is mentioned in the passage as an argument made by scientists who are unconvinced that birds evolved from theropod dinosaurs

What was the evidence or assertion used by the scientists?

The skeptical scientists used the assertion that theropods had unfused clavicles as an argument that birds could not have evolved from theropods.

[vikram4689]

agree to this statement - The skeptical scientists used the assertion that theropods had unfused clavicles as an argument that birds could not have evolved from theropods. i.e. scientists said birds cannot evolve from theropods because fused clavi in bird DIFFER from UN-fused clavi. in theropod

what i am failing to understand is how does Fused clavi. of theropod comes into picture

[anuprajan5]

Vikram,

And therein my point - what is the primary difference? The primary difference between the clavicles is that 1 is fused and the other is unfused, which is used as an argument by the scientists that birds could not have evolved from theropods. - and that is what the question asks.

The question asks - whats the evidence or the assertion in the passage that is presented by the scientists who are unconvinced that birds evolved from theropods.

[vikram4689]

ok, so do you mean that since scientist are comparing UN-fused clavi. of thero. with fused ones of birds, scientists wanted to convey that theropods did not be have FUSED clavi because in that case scientist would have compared FUSED ones of thero and birds.

[anuprajan5]

Vikram,

Let's take a step back with the question. WHat does the question ask?

Which of the following is mentioned in the passage as an argument made by scientists who are unconvinced that birds evolved from theropod dinosaurs?


So we are looking for arguments made by the scientists who are unconvinced.

Reading the paragraph, these are the arguments presented:

a. They argue that theropods appeared too late to have given rise to birds
b. Skeptics also argue that the fused clavicles (the "wishbone") of birds differ from the unfused clavicles of theropods
c. Finally, some scientists argue that the complex lungs of birds could not have evolved from theropod lungs

Taking the answer options:

(A)There are no known theropod dinosaur fossils dating from a period after the time of Archaeopteryx. - In fact they argued to the contrary. They argued that the theropods were present after the birds

(B)There are no known theropod dinosaur fossils that indicate the structure of those dinosaurs' lungs. - They don't argue this. They argue that that the complex lungs of birds could not have evolved from theropod lungs

(C)Theropod dinosaurs appear in the fossil record about 150 million years ago. - They don't argue this. This statement is a counter to their argument.

(D)Theropod dinosaurs did not have fused clavicles. - Evident from - Skeptics also argue that the fused clavicles (the "wishbone") of birds differ from the unfused clavicles of theropods

(E)Theropod dinosaurs had certain bones that look just like those of Archaeopteryx. - This is not part of the scientists argument. Instead this is a counter argument in the passage.

I hope that helps.

[vikram4689]

Anup,

i am convinced that a,b,c,e are wrong but even after doing POE and spending around 3min., i marked "b" because i could not infer anything related to fused clavi. of theropods and considered it out-of-scope. if you can tell how did you infer about fused clavi. of thero. then that would help.