Bos is often divided into four subgenera: Bos, Bibos, Novibos, and Poephagus, but including these last three divisions within the genus Bos without including Bison is believed to be paraphyletic by many workers on the classification of the genus since the 1980s. The genus as traditionally defined has five extant species,[2] but this rises to eight when the domesticated varieties are counted as separate species, and ten when the closely related Bison is also included.[3][4][5] Most but not all modern breeds of domesticated cattle (including taurine cattle and zebu) are believed to have originated from the extinct aurochs.[6][7] Others like Bali cattle and gayal are thought to have originated from South and Southeast Asian Bos species.
^Groves, C. P., 1981. Systematic relationships in the Bovini (Artiodactyla, Bovidae). Zeitschrift für Zoologische Systematik und Evolutionsforschung, 4:264-278., quoted in Don E. Wilson & DeeAnn M. Reeder (editors). 2005. Mammal Species of the World. A Taxonomic and Geographic Reference (3rd ed), Johns Hopkins University Press: "Bison". (online edition )
^Wang, K., Lenstra, J. A., Liu, L., Hu, Q., Ma, T., Qiu, Q., & Liu, J. (2018). Incomplete lineage sorting rather than hybridization explains the inconsistent phylogeny of the wisent. Communications biology, 1(1), 1-9.