How on earth did animals get to the distant islands of the earth after the flood, especially the ones which people have not yet been to?
Augustine gives many different possible reasonings, but concludes that at the end of the day that's not really the point of the story. The point is that the ark full of animals points to a church saved in Christ composed of a wide variety of peoples.
What about genetic anomalies, or even monsters (the "Cynocephalae", for one)? Did they come from Adam, or from Noah? Are they signs that God didn't know what he was doing, or made a mistake, or isn't really in control at all?
Augustine says that we miss the point here. We see one person born with "freakish" traits and cry "monster!", when in reality we lack the wide-ranging perspective that God has which might very well mean that that person, in his proper place, adds to the overall beauty of creation. "The trouble with a person who does not see the whole is that he is offended by the ugliness of a part because he does not know its context or relation to the whole." One might think here of Cindy Crawford's mole. Moles are generally considered ugly aberrations and mars on one's beauty, but I don't know that I've ever heard anyone make that claim of Ms. Crawford...
We don't need to worry about men on the other side of the world--if there are even men there at all! Let's stick to what we know, and look for the City of God where we are. (And yes, Augustine does make some geographical and scientific errors here that get compounded in the Later Middle Ages, but we can hardly blame him for accepting the science of his time or for what later writers did with his work.)