The snake and the turtles/ellies are (so far as I know) from different cultures/mythology and I haven't seen the two combined anywhere 'reliable' before...
The 2 tail-eating serpents (sometimes called an Ouroboros) as WA
says are from Norse mythology (the scandinavian creation myths also feature a giant tree - ash I think).
The turtle/elephant/disc originates in the Orient (where they have elephants of course as well as turtles) and I think it's probably Hindu in origin, although I believe the Japanese myths have turtle gods or demons - no doubt Pooh can help us out there
. The article Tony's given us also points at the Chinese and Native Americans having turtle mythology - so a popular allegorical animal-deity worldwide