Conodonts, the spiky phosphatic remains (bones and teeth composed of calcium phosphate) of tiny marine animals that probably appeared about...
GMAT Reading Comprehension : (RC) Questions
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.
According to the passage, the anatomical evidence provided by the preserved soft bodies of conodonts led scientists to conclude that
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| 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. | What it says: Scientists found spiky remains from ancient tiny sea creatures, and these fossils caused major disagreements among scientists. What it does: Introduces the main subject (conodonts) and establishes they were mysterious/controversial Source/Type: Factual background information Connection to Previous Sentences: This is our starting point - no previous information to connect to Visualization: Picture tiny spiky teeth and bones scattered on the ocean floor 520 million years ago, with scientists scratching their heads trying to figure out what they came from Reading Strategy Insight: The word "controversial" signals we're about to learn about competing theories - stay alert for different viewpoints What We Know So Far: Conodonts = spiky remains from ancient sea animals, caused scientific debate What We Don't Know Yet: Why they were controversial, what the debate was about |
| Both the nature of the organism to which the remains belonged and the function of the remains were unknown. | What it says: Scientists didn't know what animal these spiky parts came from OR what the spiky parts were used for. What it does: Clarifies and simplifies why conodonts were "controversial" Source/Type: Factual explanation Connection to Previous Sentences: This directly explains the previous sentence! Sentence 1 said "controversial" - NOW we know exactly why: double mystery (unknown animal + unknown function) Visualization: Imagine holding a spiky tooth-like object and asking: "What creature did this come from?" AND "What did this creature use it for?" Reading Strategy Insight: Feel relieved here - this is simplification, not new complexity. The author is helping us understand the controversy. |
2. Passage Summary:
Author's Purpose:
To explain how a mysterious fossil discovery resolved a long-standing scientific debate about whether vertebrates first evolved hard body parts for defense or for hunting.
Summary of Passage Structure:
In this passage, the author walks us through how scientists solved an ancient mystery and what it revealed about evolution:
- First, the author introduces conodonts as mysterious spiky fossil remains that puzzled scientists for a long time because no one knew what animal they came from or what they were used for.
- Next, the author explains that a 1981 discovery of complete fossils solved this mystery and had major implications for understanding how vertebrate skeletons evolved.
- Then, the author presents two competing theories: the traditional view that skeletons evolved for defense first and teeth came later, versus the alternative view that teeth evolved first for hunting.
- Finally, the author shows how the conodont evidence supports the hunting-first theory, since these primitive vertebrates only had hard parts in their mouths and came before armored fish.
Main Point:
The conodont fossils prove that vertebrates first evolved hard body parts in their mouths for hunting prey, not for protection, which means aggression rather than defense was the main driving force behind the evolution of vertebrate skeletons.
3. Question Analysis:
The question asks specifically what scientists concluded based on the anatomical evidence from the preserved soft bodies of conodonts discovered in 1981. This is asking for a direct cause-and-effect relationship: what did the anatomical evidence lead scientists to conclude?
Connecting to Our Passage Analysis:
From our passage analysis, we know that:
- The 1981 discovery revealed complete conodont fossils with soft body parts, not just the spiky remains
- This anatomical evidence showed conodonts had basic vertebrate features (notochord, V-shaped muscles, tail fins)
- Crucially, conodonts lacked any mineralized structures except in their mouths
- This made them more primitive than armored fish like ostracoderms
- The evidence resolved the debate between defense-first vs. predation-first theories
Prethinking:
The anatomical evidence from soft body preservation showed that conodonts were primitive vertebrates with only mouth parts mineralized, which came before the fully armored vertebrates like ostracoderms. This chronological relationship - primitive vertebrates with teeth appearing before armored vertebrates - directly supports answer choice D. The passage structure builds from the 1981 anatomical discovery to the final conclusion that teeth evolved first for predation, meaning toothed vertebrates preceded armored ones in evolutionary history.
- The passage clearly establishes conodonts as vertebrates, not invertebrates
- The anatomical evidence (notochord, V-shaped muscles, tail fins) specifically identifies them as primitive vertebrates
- This directly contradicts the passage's conclusion that conodonts were among the most primitive vertebrates
- Did you confuse conodonts with the invertebrate carnivores mentioned as threats to early vertebrates?
→ Reread the passage - invertebrate carnivores were the predators that threatened early vertebrates, while conodonts were the early vertebrates themselves - Did you miss the anatomical features that classify conodonts as vertebrates?
→ Focus on the specific vertebrate characteristics: stiffening notochord, V-shaped muscle blocks, and tail fins
- This represents the traditional theory that the passage ultimately rejects
- The conodont evidence actually disproves this idea by showing teeth came first, not from armor
- The anatomical evidence supports the opposite conclusion - that teeth were primitive features
- Did you confuse the traditional theory with what the conodont evidence actually proved?
→ Remember that conodonts resolved the debate by disproving the traditional view - Are you mixing up the old theory with the new conclusion?
→ The passage structure moves from old theory (armor first) to new evidence (teeth first)
- The passage concludes that conodonts were predators, not suspension feeders
- Suspension feeders were mentioned as part of the traditional defensive theory that was disproven
- The final conclusion emphasizes that conodonts improved efficiency as predators
- Did you associate conodonts with the early vertebrates described in the traditional theory?
→ The traditional theory described hypothetical early vertebrates, while conodonts are actual fossil evidence that disproves that theory - Are you confusing the disproven theory with the proven conclusion?
→ Focus on what the conodont evidence actually demonstrates about predatory behavior
- The anatomical evidence showed conodonts were primitive vertebrates with only mouth parts mineralized
- This placed them chronologically before armored vertebrates like ostracoderms
- The evidence directly supports the sequence: teeth-first vertebrates (conodonts) preceded armor-first vertebrates
- The 1981 discovery fundamentally changed scientists' understanding of conodonts
- Original observations were limited to just the spiky remains without context
- The soft body evidence provided completely new insights that weren't available from original observations
- Did you think the 1981 discovery just confirmed what was already known?
→ The passage emphasizes this was a breakthrough that resolved longstanding controversies - Are you underestimating how much the soft body evidence changed scientific understanding?
→ The discovery had "important implications" that completely shifted theories about vertebrate evolution