PrepTest 156, Section 2, Question 2
Body temperature can be estimated by the relative(56 more words not shown)
Which one of the following,(7 more words not shown)
- ALarge warm-blooded animals(14 more words not shown)
- BThe fossilization process(14 more words not shown)
- COxygen was more(12 more words not shown)
- DSmall warm-blooded animals(16 more words not shown)
- EWarm-blooded animals are(9 more words not shown)
Reading the argument
What if dinosaurs were different from the cold-blooded animals living today?
The scientist estimates ancient body temperatures from oxygen isotope ratios in fossil bones. Those estimates suggest that a dinosaur's arms and legs were about as warm as the rest of its body. That's unlike today's typical cold-blooded animal, whose core is much warmer than its limbs. The scientist concludes that dinosaurs were probably warm-blooded.
I can see the comparison, but why assume a cold-blooded dinosaur would have worked just like a cold-blooded animal today? Perhaps dinosaurs had some other way of keeping their body temperatures relatively even. We aren't told enough about their biology to rule that out.
What we’re looking for
For a weakener, I'd initially look for a relevant difference between dinosaurs and modern cold-blooded animals. That would challenge the comparison the argument relies on. We should still consider another answer if it gives us a different reason to distrust the conclusion.
Working the answers
- A
A slightly warmer core is compatible with having nearly the same temperature throughout the body. The passage contrasts that near uniformity with the much higher core temperature of typical cold-blooded animals. A doesn't show that dinosaurs fail to fit the warm-blooded pattern. Be careful not to turn 'nearly the same' into 'exactly identical.'
- BCorrect
This takes a different route from my prediction: can we trust the temperature estimates in the first place? The method depends on the original oxygen isotope ratios in the bones. If fossilization changes those ratios so much that we can't recover the originals, today's fossil measurements don't reliably reveal the dinosaur's body temperature.
We were trying to explain why dinosaurs had relatively uniform temperatures. B makes us question whether the fossils establish that uniformity at all. It doesn't prove that dinosaurs were cold-blooded. It undermines the evidence offered for calling them warm-blooded.
- C
More oxygen in the atmosphere is not the same as a different proportion of two oxygen isotopes in bone. C gives no connection between atmospheric oxygen abundance and the reliability of these temperature estimates. The shared word 'oxygen' doesn't supply that missing explanation.
- D
This compares mice with elephants. Our concern was whether dinosaurs could have differed from modern cold-blooded animals, and this choice doesn't address that comparison. It also doesn't tell us that the estimated dinosaur temperatures are incompatible with being warm-blooded.
- E
How much oxygen an animal uses is different from the ratio of oxygen isotopes in its bones. We aren't told how active dinosaurs were or how much oxygen they used. E therefore gives us no reason to reject the fossil-based inference. Follow what the oxygen information actually means, rather than choosing an answer simply because it repeats a familiar word.
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