In all seriousness, whatever happened to the Lion Turtles? And how many of them were there? And how did the civilizations that we all know and love spring from the (according to the Aye-Aye spirit) dozens of settlements across the world? How do you find and kill one, and why on Earth would you even try? More to the point, how is it that they could energybend?
In my own headcanon (if that's what it's called), there were not dozens, per se, but 32, each with their own population of Benders. 4 Air, 8 Fire, 8 Water, and 12 Earth, with their own cultures ten thousand years or so before the present day. That gives enough cultural innovation to make people happy, and little enough difference to keep people happy (because, after all, there's only one Air Nomad philosophy that got passed down). And it fits with the elements, too; a lighter population of Airbenders, equal numbers for Water- and Firebenders, and more Earthbenders (or at least people related to Earthbenders) than you can count on the legs of a millipede colony. But I should like to know what others think, especially as I've only tried to answer one of my questions.