The biological subfamily Bovinae includes a diverse group of 10 genera of medium to large-sized ungulates, including domestic cattle, bison, African buffalo, the water buffalo, the yak, and the four-horned and spiral-horned antelopes. The evolutionary relationship between the members of the group is obscure, and their classification into loose tribes rather than formal subgroups reflects this uncertainty. General characteristics include cloven hoofs and usually at least one of the sexes of a species having true horns. The largest extant bovine is the gaur.