I thought the lion-turtle had a sort of deity-like symbolism about him. the island on the turtle back reminded me of the eastern myth of the whole world being on the back of a turtle, and I saw that island as a sort of symbol for the whole world itself. if the avatar is the incarnation of the spirit of the world, this makes sense somehow. the lion part made me think of Christian symbolism with Jesus as Lion, or you know like in Narnia with Aslan the lion, and it seemed to me that this was sort of a symbol of a creator of the world itself... he did say that before the elements were bended, the lionturtles bent energies; it seemd to me that indicated that they were the original creators of the elements and the element benders themselves.

now, when they were tracking aang there was no scent anywhere in the whole world... but he also wasn't in the spirit world... that part is unclear to me but it indicates to me that this lion turtle is more than just a badger mole or a sky bison... he's probably some type of spirit (the way the Owl spirit appears in corporal form or how the moon and ocean spirits live in the physical world) and that being on him meant being completely disconnected from the world... by being on something that symbolized the whole world itself.