By the way, I never did notice if anyone gave the correct answer to this question -- is the hippo a pig or whale?
A hippo is neither a pig nor a whale, it's a hippo. Fossil analyses say hippos seem distantly related to both pigs and whales. But according to newer DNA analysis, they are closer to whales than pigs.
Of course, you've probably seen, whenever people ask the hippos which relative they feel closer to, their only response is a big big yawn. I guess, by now hippos are bored with the subject... ;-)
At precisely what moment did a hippo become a hippo? Exactly how different from a pig does a hippo have to be to be a hippo without turning into a whale?