The major problem faced by an intelligent elephant (if we run with the initial example here) would be manipulation of their environment; as Onionsoldier pointed out, opposable thumbs are what it's all about baby. How are they going to build hearths, shelters, clothes, cultivate the land? Those trunks they sport are only so flexible. At the end of the day you can't (naturally, as far as we know) beat a human hand when it comes to making and using tools to achieve the physical improvements in environment required to enhance the safety and quality of life. And these are necessary advances; what's the point of all that intelligence if you can't find any way to use it? Sure dolphins could be clever alright, but without the means to manipulate anything, bend and shape their world to their will (and access to fire would help here too!) they're, at best, just child-like inquisitives jumping through the surf.