PrepTest 94+, Section 2, Question 2
Body temperature can be estimated by the relative proportion of two oxygen isotopes in bone. Such estimates derived from dinosaur fossils suggest that dinosaurs had nearly the same body temperature in their limbs as in the rest of their bodies. Typically, the core body temperature of cold-blooded animals today is much higher than the body temperature in their limbs. Thus, dinosaurs were probably warm-blooded.
Body temperature can be estimated by the relative proportion of two oxygen isotopes in bone. Such estimates derived from dinosaur fossils suggest that dinosaurs had nearly the same body temperature in their limbs as in the rest of their bodies. Typically, the core body temperature of cold-blooded animals today is much higher than the body temperature in their limbs. Thus, dinosaurs were probably warm-blooded.
Body temperature can be estimated by the relative proportion of two oxygen isotopes in bone. Such estimates derived from dinosaur fossils suggest that dinosaurs had nearly the same body temperature in their limbs as in the rest of their bodies. Typically, the core body temperature of cold-blooded animals today is much higher than the body temperature in their limbs. Thus, dinosaurs were probably warm-blooded.
Body temperature can be estimated by the relative proportion of two oxygen isotopes in bone. Such estimates derived from dinosaur fossils suggest that dinosaurs had nearly the same body temperature in their limbs as in the rest of their bodies. Typically, the core body temperature of cold-blooded animals today is much higher than the body temperature in their limbs. Thus, dinosaurs were probably warm-blooded.
Which one of the following, if true, most seriously weakens the argument?
Large warm-blooded animals keep their core body temperature slightly higher than the body temperature in their limbs.
The fossilization process introduces changes to bones such that their original oxygen isotope ratios cannot be predicted.
Oxygen was more abundant in Earth's atmosphere during the period in which the dinosaurs lived.
Small warm-blooded animals like mice tend to have more uniform body temperatures than do large warm-blooded animals like elephants.
Warm-blooded animals are more active and use more oxygen than cold-blooded animals.
Explanations
The author argues that dinosaurs were probably warm-blooded. They base this claim on three ideas strung together: (1) oxygen isotopes in bone can predict body temperature; (2) estimates derived from dinosaur bones suggest dinosaurs had roughly the same body temperature in their bodies as in their limbs; (3) today's cold-blooded creatures have colder limbs than bodies.
We're asked to weaken this argument. Though we probably won't predict the answer verbatim, it's always good to go into the answer choices with some ideas in mind. So, what would weaken this argument?
For starters, I'm looking at the relationship between bones left long ago and bones found today. What if fossilization distorts the ions in the bone, not just of oxygen, but potentially all the molecules in the bone? That would call into question a key piece of evidence in this author's argument. For another, the passage points to the fact that typically cold-blooded creatures have colder limbs than bodies—what if dinosaurs share more DNA with the atypical cold-blooded creatures than the ones discussed in the passage? If that was true, that would hurt the argument.
Armed with these predictions, let's read some answer choices:
Nah, total trap answer. This doesn't do much. Who cares about "large" warm-blooded creatures? What about small ones? We know from the passage that dinosaurs (meaning all) "had nearly the same body temperature in their limbs as in the rest of their bodies." This would only call into question what's going on with large dinosaurs, at best. The rest would remain unaccounted for.
Perfect. And very close to one of my predictions. If it's true that bones change so much in the process of becoming fossils that the oxygen estimation technique is no longer trustworthy, then our author's argument makes no sense. How could we determine anything about the dinosaur's warm- or cold-bloodedness at that point? This is a devastating weakener.
Nope. This has no impact on the author's conclusion and doesn't call into question any of their premises.
No. This is another trap, like A. This only calls into question what we know about dinosaurs of various sizes. The passage talks about all dinosaurs. We need something that affects all of them.
Nah, this is extraneous to the argument, too. I don't care much about dinosaurs' oxygen consumption behaviors—just whether or not the oxygen isotope in their bones is consistent (or inconsistent) with warm- or cold-blooded creatures today.
0 Comments