The bovine family (taurids and bisonids) diverged from the common ancestral line with water buffalo and African buffalo about 5 to 10 million years ago.
 Thereafter, the family lineage of bison and taurine cattle does not appear to be a straightforward "tree" structure as is often depicted in much evolution, because evidence exists of interbreeding and crossbreeding between different species and members within this family, even many millions of years after their ancestors separated into different species.
 This cross breeding was not sufficient to conflate the different species back together, but it has resulted in unexpected relationships between many members of this group, such as yak being related to American bison, when such relationships would otherwise not be apparent.

A 2003 study of mitochondrial DNA indicated four distinct maternal lineages in subtribe Bovina:
Taurine cattle and zebu
European bison (wisent)
American bison and yak
Banteng, gaur, and gayal
However, Y chromosome analysis associated wisent and American bison.
An earlier study using amplified fragment length polymorphism  fingerprinting showed a close association of wisent and American bison and probably with yak, but noted that the interbreeding of Bovini species made determining relationships problematic.
It is shown, however, the wisent may have emerged by species divergence initiated by the introgression of bison bulls in a separate ancestral species, the aurochs.

The steppe bison (Bison priscus) diverged from the lineage that led to cattle (Bos taurus) about 2 to 5 million years ago.
 The bison genus is clearly in the fossil record by 2 million years ago.
The steppe bison spread across Eurasia and was the bison that was pictured in the ancient cave paintings of Spain and Southern France.

The European bison arose from the steppe bison, without fossil evidence of other ancestral species between the steppe bison and the European bison, though the European bison might have arisen from the lineage that led to American bison if that lineage backcrossed with the steppe bison.
 Again, the web of relationships is confusing, but some evidence shows the European bison is descended from bison that had migrated from Asia to North America, and then back to Europe, where they crossbred with existing steppe bison.
At one point, some steppe bison crossbred with the ancestors of the modern yak.
 After that cross, a population of steppe bison (Bison priscus) crossed the Bering Land Bridge to North America.
 Evidence has been found of multiple crossings of bison to and from Asia starting before 500,000 years ago and continuing until at least 220,000 years ago.
 The steppe bison spread through the northern parts of North America and lived in Eurasia until roughly 11,000 years ago and North America until 4,000 to 8,000 years ago.

Bison latifrons (giant bison or longhorn bison) is thought to have evolved in midcontinent North America from B. priscus, after the steppe bison crossed into North America.
 Giant bison (B. latifrons) appeared in the fossil record around 500,000 years ago.
B. latifrons was one of many species of North American megafauna which became extinct during the Quaternary extinction event.
It is thought to have disappeared some 21,000–30,000 years ago, during the late Wisconsin glaciation.

The B. latifrons species was replaced by the smaller Bison antiquus.
 B. antiquus appeared in the North American fossil record approximately 250,000 years ago.
 B. antiquus, in turn, evolved into  B. occidentalis, then into the yet smaller B. bison—the modern American bison—some 5,000 to 10,000 years ago.
Some researchers consider B. occidentalis to be a subspecies of B. antiquus.
The bovine family (taurids and bisonids) diverged from the common ancestral line with water buffalo and African buffalo about 5 to 10 million years ago.  Thereafter, the family lineage of bison and taurine cattle does not appear to be a straightforward "tree" structure as is often depicted in much evolution, because evidence exists of interbreeding and crossbreeding between different species and members within this family, even many millions of years after their ancestors separated into different species.  This cross breeding was not sufficient to conflate the different species back together, but it has resulted in unexpected relationships between many members of this group, such as yak being related to American bison, when such relationships would otherwise not be apparent.
A 2003 study of mitochondrial DNA indicated four distinct maternal lineages in subtribe Bovina:
Taurine cattle and zebu
European bison (wisent)
American bison and yak
Banteng, gaur, and gayal
However, Y chromosome analysis associated wisent and American bison. An earlier study using amplified fragment length polymorphism  fingerprinting showed a close association of wisent and American bison and probably with yak, but noted that the interbreeding of Bovini species made determining relationships problematic. It is shown, however, the wisent may have emerged by species divergence initiated by the introgression of bison bulls in a separate ancestral species, the aurochs.
The steppe bison (Bison priscus) diverged from the lineage that led to cattle (Bos taurus) about 2 to 5 million years ago.  The bison genus is clearly in the fossil record by 2 million years ago. The steppe bison spread across Eurasia and was the bison that was pictured in the ancient cave paintings of Spain and Southern France.
The European bison arose from the steppe bison, without fossil evidence of other ancestral species between the steppe bison and the European bison, though the European bison might have arisen from the lineage that led to American bison if that lineage backcrossed with the steppe bison.  Again, the web of relationships is confusing, but some evidence shows the European bison is descended from bison that had migrated from Asia to North America, and then back to Europe, where they crossbred with existing steppe bison. At one point, some steppe bison crossbred with the ancestors of the modern yak.  After that cross, a population of steppe bison (Bison priscus) crossed the Bering Land Bridge to North America.  Evidence has been found of multiple crossings of bison to and from Asia starting before 500,000 years ago and continuing until at least 220,000 years ago.  The steppe bison spread through the northern parts of North America and lived in Eurasia until roughly 11,000 years ago and North America until 4,000 to 8,000 years ago.
Bison latifrons (giant bison or longhorn bison) is thought to have evolved in midcontinent North America from B. priscus, after the steppe bison crossed into North America.  Giant bison (B. latifrons) appeared in the fossil record around 500,000 years ago. B. latifrons was one of many species of North American megafauna which became extinct during the Quaternary extinction event. It is thought to have disappeared some 21,000–30,000 years ago, during the late Wisconsin glaciation.
The B. latifrons species was replaced by the smaller Bison antiquus.  B. antiquus appeared in the North American fossil record approximately 250,000 years ago.  B. antiquus, in turn, evolved into  B. occidentalis, then into the yet smaller B. bison—the modern American bison—some 5,000 to 10,000 years ago. Some researchers consider B. occidentalis to be a subspecies of B. antiquus.
American bison