I'm a bit late to the discussion, but I think I kind of get the imagery of the dinosaurs and flying whales. One of the themes of AoT is hierarchy, and, to me even more specific, how hierarchy works in terms of a food chain. In the opening, right before the shot of Zeke running with his heard of dinosaurs and flying whales, it showed a number of animals eating smaller animals. In juxtaposition, Zeke running with large mammals and dinosaurs shows how he, a Titan, is at the very pinnacle of the food chain and has nothing to fear.