I am not so sure that dolphins existing out of water is such a great example considering the various conditions that they can survive in that we can't. Air v water aside, I am willing to guess humans can't stand a tenth of the pressure that dolphins can. And I am not so willing to grant that humans have such a great capacity for long distance running compared to other animals. Humans have a greater intellect, no doubt, and certainly a greater dexterity of some digits, and even a better memory, so I think all in all, it is a combination of average things that we have in a greater than average that makes us more adaptable and thus more "successful".