If I weren't you, I wouldn't break down the names of creatures. White rhinos aren't white, and jellyfish aren't fish.
But you're right, for a Sea Rex to get there, the lake would have to be a fair way above the surface of the highest of those teirs - which frankly does seem unlikely, as the entire plateau would then need to be flooded, which would cover a vast area of Mudos in water.
But then again, in MO we have native vending machines and floating metal islands.