Sforno on Genesis 7:23/ספורנו על בראשית ז׳:כ״ג

1וימח את כל היקום, the structure of all the living beings was completely dissolved, but not that of the plants. “[trunks of trees might survive in recognisable form, whereas bodies would not be recognisable. Ed.]

2This is why the Torah added the words מאדם ועד בהמה, עד רמש ועד עוף השמים וימחו מן הארץ, “man or beast, moving creatures, including the birds of the sky disintegrated completely.” No traceable remains survived.