Which biome occurs in the united states and once contained huge herds of grazing herbivores

Temperate grassland biome  

Explanation:

The temperate grasslands are referred to the biome which is comprised of vast grasslands, being the most dominant type of vegetation in the United States. There is less amount of plants and trees in this biome, and they have cold winters and hot summers. There occurs comparatively less amount of rainfall in this region that controls the height of this grasslands. The soil here is rich in nutrients that favors the growth of these vast grasslands.

This grasslands are divided into two types, namely-

(1) The Prairies- These are the grasslands that are comprised of tall grasses.

(2) The Steppe- These are the grasslands that are comprised of short grasses.

"a.) well–developed vascular system."

2%? i tried finding the exact sorry if it's not 100% correct ; -;