Never thought of that.
Sea creatures consuming most if not all is one possibility. Imagine though when the waters receded the dung, the remnants of a receding global sea.
Only God knows though.
I don't think we're meant to have all the answers. And not everything is to make sense.
The Genesis creation epic for instance.
Noah's story for that matter is predated by the epic of Gilgamesh.
I think the human condition is one fated to wonder about a few things for as long as we walk the earth.
Why are we here? And, what's the point of a higher powers ego needing to be appeased by lesser beings behaviors when that higher power created them to be a disappointment from the moment they were born?
Interestingly is that there are over 200 flood legends in different cultures all over the world.
I would say that the The Epic of Gilgamesh and other ancient writings that contain Flood stories does not call the Genesis account into question. On the contrary, it provides evidence that verifies the fact of a global Flood, and is exactly what any person who has given the idea much thought would expect to happen if the Flood were a historic reality.