First attempt at a food chain

I'll preface this by saying everything I say here is up in the air, so if you read this and think "yeah... but what about <some shit>?" feel free to lemme know.

Alright, so I'm trying to start by figuring out what this world/area/province's ecosystem looks like. In particular, the food chain. Right up at the top, apex predator, captain of the football team, homecoming king and queen, is the giant tortoise that I've yet to name. Yeah after a lot of thinking about whether they'd be carnivorous or herbivorous, I decided to go with carnivorous. 

The way I see it, is that if I'm going to fashion a whole world, I want it to not be complete bullshit. I guess that's not super groundbreaking but what I mean is that while I don't hope to create a flawless world, I at least want to make a tangible world, with enough integrity to stand up to a little prodding.

So if I'm sticking to my guns about the almost entirely (entirely?) desert world, how on earth could I hope to feed a tortoise big enough to carry a village on its back? The answer I'm most interested in right now, is basically "more giant animals". So I'm sort of creating a food chain rife with mega fauna. This also helps to contribute to why these people live the way they do. Wanna not get eaten by big animals? Live on the back of the biggest/baddest one.

So my tortoises will draw heavily from alligator snapping turtles. If you're not familiar give yourself a treat and go google those bad boys.

At this point, I'm thinking about probably including three secondary predators. One would be a carrion feeding avian, the next an animal which lives and hunts in packs, and the last a solitary animal. No 'for sures' but the pack animal will probably be a big ol' hyena, and the solitary predator might be an insect? We'll see. 

So what do all these lovely predators hunt? You ask.

Not sure.

At this point I'm planning on having four major herbivores, all of which will be mega fauna. But before I can commit to that I need to address how they survive. I'll go into that in another post so that this doesn't ramble on forever.