The answer is - because over 90% of this biome has been converted to agriculture.
This biome has been much larger before the development of the agriculture in this part of the USA, but because this biome provided large territories with deep fertile soil and predominantly lowland areas, people started using it for agriculture because it was the most suitable for that. So little by little, the biome was declining and more and more of it was becoming agricultural land.
Fossils only form if certain qualifications are met, and some organisms cannot meet them, so they just cease to exist, not a single sign of them. This could happen if they were organisms that decayed completely. Fossilization can include freezing, drying, and encasement, usually in tar or resin.
True.......................................
I think it's anemia thanks