Logical Reasoning

PT143 · S4 · Q21 In modern deep-diving

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In modern deep-diving marine mammals, such as whales, the outer shell of the bones is porous.

Conclusion

Ichthyosaurs were deep divers

Evidence

Ichthyosaurs had porous outer bones. + Modern deep diving mammals have porous outer bones.

Evaluation

This is an argument by Analogy / Comparison. Since deep-diving mammals and ichthyosaurs have one thing in common (porous outer bones), they probably have another thing in common (deep diving).

We strengthen these types of arguments by adding more similarity between the two cases. We weaken them by pointing out important differences.

Maybe porous bones are different when it comes to modern vs. prehistoric, or mammal vs. reptile. Maybe we'll learn of a different functionality for the porous bones in ichthyosaurs.

Goal

Find an answer that makes it less fair to compare Ichthyosaurs to modern deep-diving mammals, or find an answer that makes it seem like ichthyosaurs had porous bones for a different adaptive reason than deep-diving.

21.

Which one of the following, if true, most weakens the argument?

Some deep-diving marine species must
No Impact
It would hurt this argument to talk about things that had porous bones but don't deep sea dive, but this answer is talking about things that deep sea dive but don't have porous bones.
4% picked this
In most modern marine reptile
No Impact
We don't care whether porous outer bones is something most modern marine reptiles have or don't have. We care about whether deep sea diving is a trait that most marine reptiles with porous bones have or don't have.
1% picked this
Correct
In most modern and prehistoric
Why this is right
This would weaken even more if it were phrased, "for most modern and prehistoric marine reptile species that have porous outer bones, they are not deep-divers". But this still weakens by showing us that there are many examples of a prehistoric marine reptiles that have porous bones but don't deep dive. It makes it seem more speculative to go from knowing Ichthyosaur has porous bones to assuming it was a deep diver. It also suggests that these marine reptiles are evolving porous bones for a different reason than to aid with deep diving (since most non-deep divers have them).
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
76% picked this
In addition to the porous
No Impact
This could have potentially worked if it said, "whales have other qualities suited for deep diving, but ichthyosaurs don't have those other things". Since this instead just says "there's no clear evidence" we have no idea whether ichthyosaurs did or didn't share these other traits.
14% picked this
There is evidence that the
No Impact
There's a little distortion in terms here. The porous outer bones make it easy to surface. This answer choice is talking about whether their bones are light enough to allow them to surface. No one ever implied that ichthyosaurs need porous bones to surface, just that having porous bones makes it easier to surface.
5% picked this

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