Although set in Africa, non indigenous animals are seen such as Asian elephants and a jaguar.
At the end of the movie, Cheeta (who is an ape) drinks the elixir. She does not turn into a baby chimp, she becomes a monkey with a tail. The Fountain of Youth retards aging, it would not cause evolutionary regression.
Tarzan movies almost never address the issue of how "The Ape Man," living in the jungle without easy access to hot water, scissors or a razor, always managed to maintain a clean-shaven face and a perfect haircut.
Although both Tarzan and Jane are seen wearing shoes in several sequences of this film, it is never explained where they got them or who made them.