Bison occidentalis is an extinct species of bison that lived in North Americafrom about 11,000 to 5,000 years ago, spanning the end of the Pleistocene to the mid-Holocene. Likely evolving from Bison antiquus, B. occidentalis was smaller overall from its ancestor and other species such as the steppe bison. B. occidentalis had a highly variable morphology, and their horns, which pointed rearward, were much thinner and pointed than Pleistocene species of bison. Around 5,000 years ago, B. occidentalis was replaced by today's smaller Bison bison.
B. occidentalis may have declined in numbers because of competition with other grass eaters of the megafauna epoch. More recently ancient DNAstudies have proven interbreeding between B. occidentalis and ancestral modern bisons, so B. occidentalis was proposed to have been a localized offshoot of B. antiquus and part of the transition from that chronospecies to modern bisons.