Conodonts, the spiky phosphatic remains (bones and teeth composed of

I doubt with the answer given for question no 3.

Nowhere it is strictly mentioned about Ostrocoderms being the earliest primitive. It is rather a matter of debate for paleontologists with varying opinions.

bm2201:

I was not able to understand why its not B in Q.2 ((Book Question: 515)

B. contrast the traditional view of the development of the vertebrate skeleton with a view derived from the 1981 discovery of conodont remains

IMO , it clearly contrast the traditional view hold before 1981.

Please correct me , why this option is wrong.

Thanks

For question 582 ("It can be inferred that on the basis...), I am confused as to where the evidence in the passage is for choice C to be incorrect. I realize that the official answer says that teeth preceded scales, but where is this in the last paragraph?

In the line "hard parts first evolved.... and that aggression rather than protection was the driving force behind the origin of the vertebrate skeleton" --> Is this where the evidence is? I see that the "hard parts that first" comes first but there is no clear transition word such as "then" or "afterwards" to indicate when the skeleton developed (couldn't it have happened at the same time?) Thank you in advance!

Hi woohoo921,

Please refer this detailed answer by expert:
https://gmatclub.com/forum/conodonts-the-spiky-phosphatic-remains-bones-and-teeth-composed-of-c-242578-20.html#p2179425


Let me know if you still have doubts.
Thanks.

Thank you, yes I saw that before posting. Unfortunately, I am still confused on this one.

B. Ostracoderms were not the earliest vertebrates.

C. Defensive armor preceded jaws among vertebrates.

i took 8 mins to complete the passage(including answers) , got all 3 right .
What should have been the ideal time to complete the passage ?

Any suggestions GMATNinja Sajjad1994 ?

Hello GMATNinja sayantanc2k

For question 3, although I marked the correct option for Q3, I was confused between B and D. Can you help to explain how to eliminate option D?

It can be inferred that on the basis of the 1981 discovery of conodont remains, paleontologists could draw which of the following conclusions?
A. The earliest vertebrates were sedentary suspension feeders.
B. Ostracoderms were not the earliest vertebrates.
C. Defensive armor preceded jaws among vertebrates.
D. Paired eyes and adaptations for activity are definitive characteristics of vertebrates.
E. Conodonts were unlikely to have been predators.

A closer look at Question #3

Your approach to this question was sound! It's a legitimately tough question, and difficult to answer without a clear read on the passage structure and process of elimination.

The only place this discovery is explicitly mentioned is in P1, but (as you know) this isn't a situation where there's some immediate factoid that we see directly connected to the year 1981. Instead, we see this big-picture statement:

"However, since the 1981 discovery of fossils preserving not just the phosphatic elements but also other remains of the tiny soft-bodied animals (also called conodonts) that bore them, scientists' reconstructions of the animals' anatomy have had important implications for hypotheses concerning the development of the vertebrate skeleton."

This doesn't point us to something that happened in 1981. Instead, the significance of this line is why the author brings up this discovery: To call into question the existing hypotheses about why the vertebrate skeleton evolved.

OK, so let's think about this structurally. P1 tells us that the conodont discovery set up scientists (and us, the readers) to reconsider two hypotheses. P2 is all about presenting those hypotheses (which existed prior to the discovery and did not use conodonts as evidence), so we're not going to find the answer there.

But the purpose of P3 is to tell us that the hypothesis of aggressive evolution seems to be correct. And P3 delivers this statement based on the discovery of conodont remains:

"The stiffening notochord...V-shaped muscle blocks...and posterior tail fins help to identify conodonts as among the most primitive of vertebrates. The lack of any mineralized structures...indicates that conodonts were more primitive than the armored jawless fishes such as the ostracoderms. It now appears that the hard parts that first evolved in the mouth of an animal improved its efficiency as a predator, and that aggression rather than protection was the driving force behind the origin of the vertebrate skeleton."

All right! The 1981 discovery triggered a new debate over the origin of the vertebrate AND placed conodonts as one of the earliest examples of vertebrate evolution being driven by aggression.

Let's start eliminating:
Sedentary suspension feeders were mentioned in P2 as potential evidence for vertebrate evolution being defensive. It's a thing that was mentioned in the passage, but it's not a statement that we can infer on the basis of the 1981 discovery of conodont remains. Eliminate (A).

This looks good! P3 specifically tells us that conodonts were vertebrates AND were more primitive than ostracoderms. This would imply that Ostracoderms were not the earliest vertebrates, because they were predated by conodonts. Let's keep choice (B) around and keep moving.

Nope. Like choice (A), this is not a statement that we can infer on the basis of the 1981 discovery of conodont remains. It's a tempting choices, but we can eliminate (C) just like we eliminated (A).

Like (A) and (C), this choice is tempting but it's not a fact that we can infer on the basis of the 1981 discovery. Eliminate (D).

Choice (E) is totally off the rails (off the spine?). The entire point of P3 is that conodonts were evolved to be predators. This is the opposite of what this choice says, so let's eliminate (E), too.

(B) is the only choice that directly answers the question and is backed up by our understanding of the 1981 discovery's importance.

I hope this helps clarify how to stay ahead of this question! Whether or not it increases your appreciation of conodonts is up to you. I do hear rumors that they taste like chicken... :tongue_opt2