Bison are a keystone species. Their staple foods are grasses and sedges. They once roamed the North American continent in great herds, and their grazing helped shape the ecology of the Great Plains. The bisons has a large head with relatively small, curving horns. Its dark brown coat is long and shaggy on the forequarters, including the front legs, neck, and shoulders, while the rest of the body has shorter, finer hair.