Heracross and Pinsir at least have a chance to be within the same bug species. Tauros and Bauffalant aren't even related species wise. We have a chance that Miltank and Tauros can have a child together, although unlike Illumise/Volbeat and the Nidoran twins are the only two Pokemon sets that can produce Male and Female versions from either one. Meaning if you breed a Male Nidoran with Ditto you have a chance for either Male or Female to hatch and breeding the female with any compatible male Pokemon will give the Female or Male Nidoran. Volbeat and Illumise work the same. Volbeat + Ditto can give either Volbeat or Illumise (Gen 5 only) and Illumise bred with any compatible Pokemon = Illumise or Volbeat.
This is not true with Miltank and Tauros which honestly means that Gamefreak do not share with the players ideals that Mitank and Tauros are pairs. While I can see them adding a baby just to quell the raging fans...right now after this research I don't think Gamefreak acknowledges them as the same species of Pokemon like Nido and Illu/Vol.