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AbdurRakib
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Updated on: 03 Jun 2025, 06:15
Originally posted by AbdurRakib on 14 Jun 2017, 02:40.
Last edited by Bunuel on 03 Jun 2025, 06:15, edited 10 times in total.
Last edited by Bunuel on 03 Jun 2025, 06:15, edited 10 times in total.
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Question 1
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
75%
(hard)
Question Stats:
47% (03:27) correct
53%
(03:37) wrong
based on 8702
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Date
Time
Result
Not Attempted Yet
Question 2
E
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Difficulty:
35%
(medium)
Question Stats:
60% (01:10) correct 40%
(01:21) wrong
based on 10089
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Date
Time
Result
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Question 3
B
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Difficulty:
55%
(hard)
Question Stats:
56% (01:22) correct 44%
(01:32) wrong
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Not Attempted Yet
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.
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. 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
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. 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
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. 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. 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
27 Sep 2018, 13:13
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So what the heck is up with Question #2?
csaluja
PAVANIJOSHI374
Izzyjolly
manishk30
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:
Quote:
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.
Quote:
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:
Quote:
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).
Quote:
(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.
Quote:
The author didn't write the second paragraph in order to contrast the characteristics of these two groups. Eliminate (C).
Quote:
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.
Quote:
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...
Question 1
aviejay
Quote:
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:
Quote:
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.
