Bison evolved from the bovine family that includes cows and other buffalo. 220,000 years ago ancestors of the North American bison, Bison Priscus, crossed the bearing land bridge into North American. Like many other animals, they migrated south where the harsh environment of ice age North America began to select for more imposing traits. Like other ice age mammals, the Bison grew into megafauna. Bison latifrons, standing 9 feet tall and with 6 foot wide horns, Bison latifrons was one of the largest bovines to ever live.