Bison, According to several authors, the re’em of the Bible. It belongs to the same genus as the aurochs, but being indigenous to America (whence its name, bos americanus), and specifically different from the aurochs, cannot possibly have been known by the Hebrews.

Source: [http://en.wikipedia.org/wiki/List_of_the_animals_in_the_Bible]

While these are like regular cattle (cows) they are wild, usually larger than domesticated cows.