I just had a quick comment. In all the Evolution vs. ID debates I've heard, when the creationists start demanding transitional forms, the best retorts I've heard are that all living things are transitional forms and examples of recently more complete branches of the Tree assembled from fossil finds. But I'm very surprised to have never heard a list like this one: penguins, flying fish, flying squirrels, bats, frogs, toads, salamanders, sea otters, walruses, etc. Yes, I know they're not riding a fence between one species and another, but they would seem to be the perfect and existing examples of how transitions could very likely take place. Polar bear fur + porcupine quills + bird feathers would also strike me as somewhat interesting.