That is your assumption, but since dinosaurs are extinct, and there was no *pre-Adamic earth* (Exodus 20:11), you can draw your own conclusions.
And God said unto Noah, The end of all flesh is come before me; for the earth is filled with violence through them; and, behold, I will destroy them with the earth.... And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female. Of fowls after their kind, and of cattle after their kind, of every creeping thing of the earth after his kind, two of every sort shall come unto thee, to keep them alive... And all flesh died that moved upon the earth, both of fowl, and of cattle, and of beast, and of every creeping thing that creepeth upon the earth, and every man: All in whose nostrils was the breath of life, of all that was in the dry land, died. And every living substance was destroyed which was upon the face of the ground, both man, and cattle, and the creeping things, and the fowl of the heaven; and they were destroyed from the earth: and Noah only remained alive, and they that were with him in the ark. (Gen 6:13,19,20; 7:21-23).
Two of every sort would be a pair of dinosaurs. "Kind" means species in Genesis. The rest of those creatures died in the Flood. And even these -- had they multiplied -- died out eventually (possibly hunted into extinction). But during the Flood, there was rapid burial in millions of tons of water, and produced fossilization and that is what is found today.