From a quote by Caesar at the site you linked for Aurochs....
The horns, in amplitude, shape and species, differ much from the horns of our oxen.Oxen look like cows to me...so where did THEY come from?
There is a reason
oxen look like cows, or more specifically, steers. Any steer yoked to pull something is an ox. Oxen are not a breed or bovine species. Oxen came from the same place the cows came from.