Bison occidentalis is an extinct species of bison that lived in North America during the Pleistocene. It probably evolved from Bison priscus. B. occidentalis was smaller, and smaller-horned, than the steppe bison. Unlike any bison before it, its horns pointed upward, parallel to the plane of its face from nose to forehead, instead of pointing forward through that plane. Around 5,000 years ago, B. occidentalis was replaced by today's smaller Bison bison. It has been theorized that B. occidentalis declined in numbers because of competition with other grass eaters of the megafauna epoch.