The bison's coat is a combination of guard hairs and a woolly undercoat. The forequarters, the head, the shoulders and the front legs are covered with a long curly and woolly dark brown or black mane. Their muzzle is black and hairless and their tongue is narrow, long and blue. It takes six and a half years for their permanent teeth to fully develop. The bison doesn't have upper incisors. The newborn calf has a cinnamon-coloured (ochre) coat until the age of 4-6 months. The wisent, it's European cousin, has no difference in colour between birth and maturity.

The bison, like all ruminants, has a four-chamber stomach. The rumen (the paunch), the reticulum (second stomach), the omasum and the abomasum (fourth stomach). With a rumen larger than that of beef cattle, the bison can take better advantage of the ingested fibres. The bison's oesophagus is twice as large as that of a cow which multiplies the entry of air and, consequently, improving their stamina. The plains bison differs from the wood bison by it's longer beard and legs covered with long hair. The wood bison is characterized by it's more pronounced withers. Furthermore, the wood bison's hair is longer and lower on it's body than it's plains counterpart. The wood bison's horns are longer and greatly exceed the width of their head. The wood bison also has a darker coat than the plains bison.