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

Question

Conodonts, the spiky phosphatic remains (bones and teeth composed of calcium phosphate) of tiny marine animals that probably appeared about 520 million years ago, were once among the most controversial of fossils. Both the nature of the organism to which the remains belonged and the function of the remains were unknown. 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.

The vertebrate skeleton had traditionally been regarded as a defensive development, champions of this view postulating that it was only with the much later evolution of jaws that vertebrates became predators. The first vertebrates, which were soft bodied, would have been easy prey for numerous invertebrate carnivores, especially if these early vertebrates were sedentary suspension feeders. Thus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were secondary features, adapted from the protective bony scales. Indeed, external skeletons of this type are common among the well-known fossils of ostracoderm, jawless vertebrates that existed from approximately 500 to 400 million years ago. However, other paleontologists argued that many of the definitive characteristics of vertebrates, such as paired eyes and muscular and skeletal adaptations for active life, would not have evolved unless the first vertebrates were predatory. Teeth were more primitive than external armor according to this view, and the earliest vertebrates were predators.

The stiffening notochord along the back of the body, V-shaped muscle blocks along the sides, and posterior tail fins help to identify conodonts as among the most primitive of vertebrates. The lack of any mineralized structures apart from the elements in the mouth 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.   1 
 1. According to the passage, the anatomical evidence provided by the preserved soft bodies of conodonts led scientists to conclude that

A. conodonts had actually been invertebrate carnivores
B. conodonts' teeth were adapted from protective bony scales
C. conodonts were primitive vertebrate suspension feeders
D. primitive vertebrates with teeth appeared earlier than armored vertebrates
E. scientists' original observations concerning the phosphatic remains of conodonts were essentially correct

2 
 2. The second paragraph in the passage serves primarily to

A. outline the significance of the 1981 discovery of conodont remains to the debate concerning the development of the vertebrate skeleton
B. contrast the traditional view of the development of the vertebrate skeleton with a view derived from the 1981 discovery of conodont remains
C. contrast the characteristics of the ostracoderms with the characteristics of earlier soft-bodied vertebrates
D. explain the importance of the development of teeth among the earliest vertebrate predators
E. present the two sides of the debate concerning the development of the vertebrate skeleton

3 
 3. 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.

RC00073-01
RC00073-03
RC00073-08

GMATNinja · Accepted Answer

So what the heck is up with Question #2? Indeed, the formatting for this particular passage makes it very tough for us to tell where one paragraph begins and the other ends. ( Bunuel , any idea how to fix the formatting? You're the best technical wizard in the GMAT Club family.

) Anyway, a closer look at the 2018 OG reveals that: Paragraph 1 ends with the words, "development of the vertebrate skeleton." Paragraph 2 ends with the words, "the earliest vertebrates were predators." Paragraph 3 begins with the words, "The stiffening notochord." Here's paragraph 2 (P2) in full: This clarification might resolve a lot of doubts about the passage and question #2. But let's break it down to eliminate any lingering confusion. OK, so why did the author write this paragraph? P1 has already told us that the 1981 discovery -- of conodont remains along with conodont fossils -- has had important implications for hypotheses about the vertebrate skeleton. In P2, the author then presents two opposing hypotheses about the vertebrate skeleton: The traditional view that it was a defensive development and an opposing view that the skeletal adaptations were part of a predatory evolution. The author offer some details for each side's hypothesis, but the point of the paragraph is to show us these two sides. Let's see which answer choices line up with our understanding: Nope! P2 doesn't outline the significance of this discovery in any way. The reason that the author writes P2 is to tell us about opposing hypotheses, not get further into the details of the 1981 discovery. Eliminate (A). (B) is very tempting, but when you read closely, two thoughts should come to mind: Is the author writing P2 to contrast two views? Are the views being contrasted "the traditional view of development of the vertebrate skeleton" and "a view derived from the 1981 discovery" ? You could argue that yes, the author is contrasting two hypotheses. And one of those hypotheses is the traditional view of how and why the vertebrate skeleton developed. We are close to keeping this answer choice. But when you refer back to the passage, was the second view (of early vertebrates as predators) "derived from the 1981 discovery"? Not quite. The second paragraph doesn't create a link between the view of predatory evolution and the 1981 discovery of conodont remains. The second paragraph doesn't even mention conodonts. That's why we eliminate (B) -- or at the very least, avoid falling in love with (B) right away. The author didn't write the second paragraph in order to contrast the characteristics of these two groups. Eliminate (C). Choice (D) tempts us by identifying a thing that the author did in P2 . But this choice doesn't tell us the reason why the author wrote P2 . Because (D) is not answering the question we were asked, we can eliminate it without hesitation. Here we are! Choice (E) does seem similar to Choice (B), but it doesn't make the mistake of naming the wrong sides of this debate. Instead, (E) matches exactly what we know: The author wrote the paragraph in order to present two opposing hypotheses. This answers the question directly, doesn't add any erroneous wrinkles, and doesn't get stuck on narrow details that miss the purpose of the paragraph. That's why (E) is distinct from (B) and (D). That's also why (E) is the best available choice. I hope this explanation turned your "conodon'ts" into "can dos"! Please forgive my humor, it's an evolutionary defense mechanism against eye-burning GMAT passages. And I'm practicing my terrible "dad jokes" for when my daughter is old enough to understand them and roll her eyes at me...

GMATNinja · Answer

Question 1

This is a sneaky one... indeed, the  traditionalists  would agree with choice (B). But the anatomical evidence provided by the preserved soft bodies of conodonts caused scientists to  question  the traditional views:

So now we have to consider the new evidence, which is NOT phosphatic (i.e. not the bones and teeth). This new evidence includes paired eyes, muscular adaptations for active life, the stiffening notochord along the back of the body, V-shaped muscle blocks along the sides, and posterior tail fins. The evidence from these non-phosphatic remains suggests that conodonts actually came BEFORE the armored jawless fishes such as the ostracoderms.

In other words, in light of the new evidence, other paleontologists argued that "teeth were more primitive than external armor." This new theory contradicts that of the traditionalists and the statement in choice (B). Thus, (B) should be eliminated.

GMATNinja · Answer

Passage breakdown 
In the first paragraph (P1), the author  introduces a debate:

There are different hypotheses concerning the development of the vertebrate skeleton. 
 A 1981 discovery regarding conodonts has "important implications" regarding this debate.

In the second paragraph, the author  explains both sides of the controversy

The  traditional view : that the vertebrate skeleton was first developed for  defense  
 The  other view : that it was developed for  predation . 
 The author then provides evidence for each side from BEFORE the 1981 discovery.

In the third paragraph, the author  argues that the 1981 discovery supports the "other view"

The vertebrate skeleton was developed for predation/aggression, not for defense.

For more on the process of breaking down RC passages, check out  this article  and  our live RC videos .

Valhalla · Answer

Please comment on answer as I have not purchased OG to double check my reasoning.

Tone: Evaluate
Organization:
P1: Describe the significance of a discovery that led to some hypotheses.
P2: Describe 2 hypotheses - traditionalists view and paleontologists view. Authors seems to favor paleotologists' view.

Topic: Discovery of fossils
Scope: Development of vetebrate skeleton based on discovery.

1. D
Uncertain between choice B and D.
B. conodonts' teeth were adapted from protective bony scales
Thus, traditionalists argued, these animals developed coverings of bony scales or plates, and teeth were secondary features, adapted from the protective bony scales.

D. primitive vertebrates with teeth appeared earlier than armored vertebrates 
The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more primitive than the armored jawless fishes such as the ostracoderms.

Remarks: 
Is it always the case that the credited answer is what the author actually intends to support? I finally choose E because the whole passage are gears towards paleontologist view and traditionalists view is just for evaluation, that is, initially it was thought, then (MAIN CONCLUSION).
Furthermore, there is the word indicate which can be concluded as conclude in this case?

2. E present the two sides of the debate concerning the development of the vertebrate skeleton
Uncertain between A and E.
A. It does actually use findings to support each argument.
E. It is mainly about presenting 2 different view using the same evidence?

Remarks:
Chosen E because it encompasses 2 views and is more general. 
Usually function question does not include details in the answer.

3. B. Ostracoderms were not the earliest vertebrates.
The lack of any mineralized structures apart from the elements in the mouth indicates that conodonts were more primitive than the armored jawless fishes such as the ostracoderms.

Although I have obtained all credited answer ,but I did not complete in the recommended time.

anje29 · Answer

Official explanation is here https://books.google.co.in/books?id=f5v ... &q&f=false

TheMechanic · Answer

There could be a huge debate of where the 2nd passage starts and where it ends. I even looked in official guide 2018 where it can be horridly concluded that the 2nd passage end in line 29.

I just got lost and selected a wrong answer choice. I hope I don't see such instances of bad formatting in actual GMAT.

BillyZ · Answer

Extra reading https://uahost.uantwerpen.be/funmorph/ra ... ll1995.pdf

manishk30 · Answer

Same thing happened with me. I also thought that the para 2 is ending at line 29 and chose the wrong option on that basis.

JS1290 · Answer

GMATNinjaTwo ,

Hi GMATNinja, I was wondering could you please explain the difference between option B and E for Q2? I ended up picking option E but it was more of a lucky guess. Would greatly appreciate it if you could please shed some light on option B especially!

PAVANIJOSHI374 · Answer

Hi,

I have a similar doubt.. For Q2, option B & option E are very similar.
How does one choose the right one? 
Please help!!

Izzyjolly · Answer

Question 2
(Book Question: 515)
The second paragraph in the passage serves primarily to
A. outline the significance of the 1981 discovery of conodont remains to the debate concerning the development of the vertebrate skeleton
B. contrast the traditional view of the development of the vertebrate skeleton with a view derived from the 1981 discovery of conodont remains
C. contrast the characteristics of the ostracoderms with the characteristics of earlier soft-bodied vertebrates
D. explain the importance of the development of teeth among the earliest vertebrate predators
E. present the two sides of the debate concerning the development of the vertebrate skeleton

I was down to B and D and ended up choosing B because I thought that the 2nd passage end in line 29. 
How can we eliminate option B here? Please help.

Rebekah · Answer

Can someone explain the third question? I got it right, but I spent almost 3 mins on this one. I had difficulties in locating where should I refer to answer this question.

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.
DPaired eyes and adaptations for activity are definitive characteristics of vertebrates.
E Conodonts were unlikely to have been predators.

I found the discovery in p1 and p3. p1 just states that the discovery changes the views scientists hold about the development of vertebrate animals. p3 seems talk about the discovery(in a vague and subtle way, there is no obvious link between the discovery talked about in p1)

Cheers!

GMATNinja · Answer

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...

shabuzen102 · Answer

Hi GMATNinja , Thank you for the very clear explanation. Everything makes perfect sense, except for the way the question is phrased "According to the passage, the anatomical evidence provided by the preserved soft bodies of conodonts led scientists to conclude that" They talked about the PRESERVED SOFT BODIES, of conodonts, which I couldn't find anywhere. That whole paragraphs talked about the preserved remains of soft-bodied animals, not preserved soft bodies (which I don't think is possible either since soft bodies have no fossils, they would just debiograde): 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, How can I make sense of this wording of the question? May I also ask what exactly do they mean "also called conodonts"? The remains of the tiny-soft bodied animals are also called conodonts, or just the tiny soft-bodied animals are called conodonts? The very first lines seemed to refer to conodonts as remains, not the animals. So what exactly do they mean by conodonts here, and "the preserved soft bodies of conodonts"? Please help

Thank you very much!

GMATNinja · Answer

Two different things in the passage are referred to as "conodonts":

1) "the spiky phosphatic remains (bones and teeth composed of calcium phosphate) of tiny marine animals"; AND
2) "tiny soft-bodied animals (also called conodonts)"

So, the word "conodont" refers to BOTH the phosphatic remains of certain tiny animals, and to the tiny animals themselves.

In 1981, scientists discovered fossils that preserved both the phosphatic and "other" remains of the tiny animals. These additional remains were, in fact, softer tissues, including a "notochord along the back of the body, V-shaped muscle blocks along the sides, and posterior tail fins." (Side note: soft tissues can indeed be fossilized -- read about dinosaur soft-tissue fossilization  here.  Apparently it is uncommon for soft tissues of land-dwellers to be fossilized unless the animal "suffer  a rare catastrophic burial -- such as death by landslide." Good stuff.)

Question #1 asks about the "preserved soft bodies of conodonts," which we know to be the fossils discovered in 1981.

I hope that clears it up!

IloveMBA123 · Answer

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.

GMATNinja · Answer

An inference, by definition, does not need to be explicitly stated in the passage. And while paleontologists once had two hypotheses, the passage definitely supports one, namely that ostracoderms were not the earliest vertebrates. Take a look at  our previous post  where we discuss this question in a bit more detail, and let us know if you have any more questions!

Teitsuya · Answer

Hi  GMATNinja

"P2 is all about presenting those hypotheses (which existed prior to the discovery and did not use conodonts as evidence)"
Which `s word/phase specifically mentioned that P2 were the hypotheses before the discovery 1981?

GMATNinja · Answer

P2 presents two hypotheses:

First hypothesis: how vertebrate skeletons  "had traditionally been"  regarded,  
 Second hypothesis: the viewpoint argued by "other" paleontologists.

Because the first hypothesis describes how skeletons HAD BEEN regarded, we know that this viewpoint existed BEFORE the 1981 discovery. And because the second viewpoint is presented as a counterpoint to this first view, we know that these two positions existed at the same time as one another.

So, the overall timeline goes something like:

Paleontologists take up two different positions regarding the vertebrate skeleton. 
 Then, there's a discovery in 1981. 
 This discovery supports one position over the other position.

I hope that helps!

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

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GMAT Reading Comprehension (RC) Questions

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

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