This episode of Tarzan leans on the lost civilization trope, which was big in Edgar Rice Burroughs' books, but not in many of the varies eras of Tarzan movies.
However, it also brought up the old concept of the Elephant's Graveyard, which was a big element of a couple of the Jonny Weissmuller movies but never appeared in the books. LOL
The problem I had with the episode is a mastodon connected with the lost city. What's the problem? You can't have "just one" of an ancient animal that's out of place. It had to have parents. If it had parents, there would be more. It's similar to King Kong. If you're going to have a giant anything, where are the parents. :-)
Otherwise, this was an average episode of the series, thought they did stretch a bit to have an army of animals face off against an army from the lost city.