Tauros is a Normal-type region-exclusive Pokémon from the Kanto region. It does not evolve into or from any other Pokémon.

Does Tauros evolve?

This Pokémon does not evolve.

Is Bouffalant the evolved form of Tauros?

They are basically the same species (cow) but with vast gender differences. Bouffalant is 50/50 So if Tauros does end up evolving into Bouffalant, then Miltank will too.