Trilobyte. You suggested the koalas got back to Australia via the Torres Strait landbridge. Unfortunately for your argument this would merely help them to move between New Guinea and Australia. If the ark finished up anywhere else they could not have got to Ozzie.

Your duck ideas. What you have called "subfamilies" are a mixture of subfamilies and tribes. More to the point though do you mean to say that ducks as different as shelducks, diving ducks, dabbling ducks, pochards, perching ducks, eiders, etc. all evolved from just one pair of birds with a maximum possible genetic variation of just four genes for each characteristic, no mutations involved?