Bovina is a subtribe of the Bovini tribe that generally includes the two living genera, Bison and Bos. However, this dichotomy has been challenged recently by molecular work that suggests that Bison should be regarded as a junior synonym of Bos. Wild bovians can be found naturally in North America and Eurasia.
The bovinans have a rich fossil record. According to the fossil record and molecular studies, Bubalina and Bovina diverged from one and another from a common ancestor around 13.7 million years ago in the Late Miocene. After arriving into Africa there was a rapid radiation of bovinan species in Africa in the Middle Pliocene. Among the diverse genera of African bovinans were two significant genera: Pelorovis and Leptobos. According to anatomical and morphological study on the various species of Pelorovis and Leptobos, it is believed the former genus evolved into Bos while the latter genus evolved into Bison during the Late Pliocene of East Africa. Both lineages then left Africa and into Eurasia at the end of the Pliocene. While Bosinhabited much of Eurasia, some species of Bison had colonized North America by crossing over the Bering Land Bridge in two waves, the first being 135,000 to 195,000 years ago and the second being 21,000 to 45,000 years ago. The exact relationships between fossil and extant bovinans problematic. Below is the list of fossil species that have been described so far :
In 1945 American paleontologist and mammalogist George Gaylord Simpson had considered there to be three genera of bovinans. In addition to recognizing Bos and Bison, he assigned the several Asiatic tropical species such as gaur and banteng into the genus Bibos. The German zoologist Herwart Bohlken also agreed with these conclusions, though he believed that the two bison species should be lumped into Bison bison. The kouprey was not included in Simpson's taxonomy, while Bohlken considered the species to be a hybrid between banteng and cattle. Below is the Simpson taxonomy:
However recent molecular work on mitochondrial DNA and the Y-chromosome has completely revamped the evolutionary relationships among bovinans. These studies support of not only the inclusion of bison species into the genus Bos, but offer two radically different positions for the European bison. According to the mitochondrial DNA, these studies support the American bison being closely related to the yak, while the European bison is more related to the aurochs. However a 2008 phylogenetic study using the Y-chromosome found the two bison species to form a clade. It also found that the yaks are an outgroup in relation to the rest of the bovinans, supporting their classification in the genus Poephagus. Another study by Hassanin et al. using autosomal introns found support in the bison-yak clade. This suggests the mitochondrial genomes is result of incomplete lineage sorting during divergence of Bos and Bison from their common ancestors rather than further post-speciation gene flow. There is evidence of limited gene flow from Bos primigenius taurus could account for the affiliation between wisent and cattle nuclear genomes. These phylogenetic studies lead Groves and Grubb, who conducted large scale taxonomic analysis on the world's ungulate species, to recommend classifying the two bison species as members of the genus Bos. Below is the listing of species recognized by Groves and Grubb with species names following Castelló from Bovids of the World:
