I'm skeptical. a 4 pound, 6 inches tall dog mounting a 180 lb, 35 in. tall bitch?
You ignore the main point, which was that the extreme morphological variation within a species (and both Chihuahuas and Great Danes are canis familiaris) makes constructing a phylogeny from the fossil 'record' an absurdity. The mechanics of such a fertilization are irrelevant.
If Chihuahuas and Great Danes are not both canis familiaris, then show it. Otherwise, your feigned skepticism is just evo irrelevancy double-talk.