PrepTest 142, Section 2, Question 12
Shark teeth are among the most common vertebrate(15 more words not shown)
Which one of the following,(11 more words not shown)
- AUnlike the bony(23 more words not shown)
- BThe rare fossilized(22 more words not shown)
- CFossils of sharks'(13 more words not shown)
- DSome species of(13 more words not shown)
- EThe physical and(21 more words not shown)
Reading the argument
A shark has many teeth but only one skeleton. Could that explain why teeth are so much easier to find?
That's my first thought. If sharks also replace teeth during their lives, one animal might leave many opportunities for a tooth fossil. We'd still want to know whether that explains the entire pattern, including why shark skeletons are rare compared with other vertebrate skeletons.
What we’re looking for
For this paradox question, keep both facts: shark teeth are common fossils, and shark skeletons are comparatively rare. The explanation needs a difference that makes those findings fit together. The number of teeth is one possible direction; the answers might offer another.
Working the answers
- ACorrect
This gives us a difference in preservation. Shark skeletons are cartilage, whereas other vertebrates have bony skeletons. Teeth and bone are much more likely to fossilize than cartilage.
So finding lots of shark teeth needn't mean we should find lots of shark skeletons. The teeth preserve more readily than the cartilage does. The same distinction also explains why shark skeletons are rare among vertebrate skeletons: the other animals' bones have a better chance of fossilizing. That addresses both comparisons without claiming cartilage can never fossilize.
- B
Different locations don't explain different numbers. We could find the few skeletons somewhere else and still wonder why they are so scarce. B tells us where fossils occur, not why teeth preserve so much more abundantly.
- C
Difficulty distinguishing teeth doesn't establish that the fossils were misidentified. The passage gives us the abundance of shark teeth as a fact to explain. C also supplies no explanation for the relative rarity of shark skeletons.
- D
This resembles the initial prediction: repeated sets of teeth could help explain why one shark leaves more teeth than skeletons. But it describes some species alive today, without establishing the same pattern among the sharks responsible for these fossils. And even a large number of teeth doesn't explain why shark skeletons are unusually rare compared with other vertebrate skeletons. A directly addresses preservation and covers both parts of the puzzle.
- E
Saying the processes occur equally often doesn't give us the needed reason for different fossil abundances. Their frequency isn't necessarily the same as the chance that a particular material becomes a fossil. A supplies that missing material difference; E doesn't explain why teeth and skeletons have such different outcomes.
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