Why do you think that species living far apart, like the Bison and the Yak, would share similar characteristics

In general, bison are larger than yaks. Sexually mature male bison weigh anywhere from 1,100 to 2,000 pounds, depending on age. Females weigh 700 to 1,200 pounds. Sexually mature male yaks weigh 650 to 800 pounds; the females weigh 400 to 700 pounds. Bison have dark brown hair that can appear black from a distance, especially in the winter when the thicker undercoat is in place. Domesticated yaks vary in color from light tan to dark brown as well as black, which is the dominant color seen in wild herds. A yak's tail is long and very thick with silky hair similar to that of a horse. In contrast, a bison has a short, stubby tail that most generally sticks out in a position horizontal to its body.