To add onto this: Not only are they on the same routes in Gen 7 but they even have the same Pokedex page like Oranguru and Passimian doMiltank for Tauros seems like a sure-bet. Since their inception the only time they aren't connected at the hip was gen 3, because gen 3 was a mess of distiribution, and Let's Go because literally no one other than gen 1 & meltan/melmetal got to be in
otherwise
gen 2: same routes
gen 4: same routes
gen 5: Same Dream World area
gen 6: same route
gen 7: same routes
They really should have jsut gone whole-hog and make them an actual "same species", like volbeat & illumise or the nidorans are.