 Wood bison is potentially more primitive in phenotype than plains bison while the latter probably evolved from mixing of "Bison occidentalis" and "Bison antiquus".In comparison to plains bison ("B.b.bison", the other surviving North American subspecies/ecotype), the wood bison is larger and heavier, with large males reaching in body length with tails and tall at withers and in weight, making it morphologically more similar to at least one of chronological subspecies of ancestral steppe bisons ("Bison priscus" sp.