Yellowstone is home to two species of bears: grizzly bears and black bears. Of the two species, grizzly bears have a much smaller range across the United States. The grizzly bear is typically larger than the black bear and has a large muscle mass above its shoulders; a concave, rather than straight or convex, facial profile; and much more aggressive behavior. The grizzly bear is a subspecies of brown bear that once roamed large swaths of the mountains and prairies of the American West. Today, the grizzly bear remains in a few isolated locations in the lower 48 states, including Yellowstone.In coastal Alaska and Eurasia, the grizzly bear is known as the brown bear.