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Question

Difficulty: HardWeaken

Paleontologists studying the extinct giant deer *Megaceros* found that fossil tooth enamel from 14,000 years ago exhibits a sharp increase in microscopic scratches and pits compared to older specimens. In modern herbivores, such abrasive wear is caused almost exclusively by chewing tough steppe grasses rather than soft forest foliage. Because regional climates became increasingly arid around that time, paleontologists concluded that shrinking forests forced *Megaceros* to shift its primary diet from forest foliage to steppe grasses.

Which of the following, if true, most seriously weakens the paleontologists' argument?

  1. A
    Skeletal remains of *Megaceros* from the late Pleistocene show changes in limb bone structure indicating that the animals traveled significantly greater daily distances to forage.
  2. B
    Regional sediment cores dating to 14,000 years ago show a severe decline in tree pollen accompanied by a rapid proliferation of abrasive steppe grasses.
  3. Intense dust storms began depositing thick coatings of abrasive mineral silt onto the canopy foliage of regional forests roughly 14,000 years ago.Answer
  4. D
    Steppe grasses were completely incapable of providing sufficient caloric nutrition to support any large herbivorous mammal during the late Pleistocene.
  5. E
    Dental micro-wear analysis is incapable of distinguishing between abrasions shallower than five micrometers on fossilized enamel.

Answer

The argument is most seriously weakened by the statement that intense dust storms began depositing abrasive mineral silt onto forest foliage around 14,000 years ago.
The conclusion claims that *Megaceros* changed its primary diet from forest foliage to steppe grasses based entirely on increased tooth wear. Showing that abrasive mineral silt coated forest leaves provides an alternative explanation for the tooth wear that does not require any change in diet, thereby substantially weakening the paleontologists' conclusion.

Step-by-Step Solution

1
Deconstruct the argument into premises and conclusion
Premises: *Megaceros* teeth from 14,000 years ago show increased abrasive micro-wear; in modern herbivores, such wear is caused by eating tough grasses; climate became arid. Conclusion: Shrinking forests forced *Megaceros* to shift its diet from forest foliage to steppe grasses.
Identifying the core premises and conclusion exposes the inferential gap between observed tooth abrasions and the assumed cause.
2
Identify the unstated assumption linking the premises to the conclusion
The author assumes that abrasive steppe grass consumption was the only plausible cause of the increased dental scratches and pits in *Megaceros*.
Weaken questions require targeting the unstated assumption by finding an alternative explanation or counterexample.
3
Evaluate the answer choices to identify the alternative cause
Abrasive mineral silt deposited on regular forest foliage explains the dental abrasions while allowing the deer to maintain their original forest diet.
Introducing a viable alternative cause directly severs the link between the dental wear evidence and the dietary shift conclusion.

Key Concept

Alternative Explanations in Causal Reasoning
Estimated Time:1m 45s
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Weaken

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