Shouldn't the low-res summaries for paragraph 3 say something like "support for one of the first two perspectives?" Maybe I'm missing something but I thought that we didn't have reason to believe that the 3rd paragraph indicated support for one of the first two perspectives over another, just that it anti-supported the third perspective.

This makes perfect sense to me. Upon blind reviewing this question I eliminated D (which I had incorrectly selected as the right answer) for exactly the reason you give -- that whales are only an example of the set of modern marine mammals, and the analogy is strictly between modern marine mammals and this prehistoric marine reptile. Drawing a dissimilarity between whales and the prehistoric reptile does not necessarily mean that this dissimilarity either matters for the purposes of the argument nor is representative of the actual class being analogized. I'm not sure if this logic is foolproof but it definitely makes sense to me.