Q21 - Ichthyosaurs and Fish

[nandy_millette]

So I got this question correct and I am just wondering if my reasoning is accurate.

So this is a Must Be True question and the stimulus is based on comparison so from my experience, the correct answer choice will highlight something this is similar or different about the things being compared as stated in the stimulus, or some other general statement based on a similarity or difference highlighted in the stimulus.

Stimulus
Icth and fish are similar due to convergence
Convergence-->Different species in the same environment independently develop similar features
Icth and fish belong to different classes of organisms-->Icth Marine Reptile
Icth and fish have fins

A-Out of scope-->the stimulus focused on species of different organisms, so much cannot be inferred about species of the same organism. Also words such as "all" and "most" made this answer choice unattractive to me.

B- Same reasoning as A above.

C-The stimulus focuses on one way that different classes of organisms can develop similar features however we cannot infer that that is the ONLY way.

E- Although the stimulus was based on the fact that Icth and Fish are different, it did not elaborate on the extent of that difference. The stimulus only stated that Icth are marine reptiles and fish are not. So its difficult to say that different organism WILL have SEVERAL different external body features. Additionally, we only know about Icth and Fish not all organisms.

So here is where I was stuck, I was able to eliminate all the above so I was left with D, but I am not sure if I understand why this is the correct answer choice. Here is my reasoning:

D is correct because Icth and Fish have similar body features yet still they are not in the same class of organism. So from this information, we can safely conclude that having similar body features does not guarantee that two species will be in the same class.

Am I right?

[christine.defenbaugh]

Hot stuff nandy_millette!! Excellent breakdown of a tough inference question!

The only substantive comment I have is that you should be wary of making predictions on inference questions. Even if you've seen a strong pattern relating to comparisons, the truth is that they would be within rights to ask you any valid inference stemming from any of the information in the stimulus - even if that information only related to fish and not ichthyosaurs, for instance.

But great work muscling through the eliminations! Also, you seemed unsure of the justification for (D), but your reasoning is spot on. If one or more similar body features were enough to determine that two organisms belonged to the same class, fish and ichthyosaurs would be in the same class. But they aren't! So that must not necessarily always be true.

Keep it up!

[nandy_millette]

The only substantive comment I have is that you should be wary of making predictions on inference questions. Even if you've seen a strong pattern relating to comparisons, the truth is that they would be within rights to ask you any valid inference stemming from any of the information in the stimulus - even if that information only related to fish and not ichthyosaurs, for instance.

I understand, predicting answers is not always wise.

Excellent breakdown of a tough inference question!