We saw in the earlier posts the similarity between:
Baptornithidae (Hesperornithes) AND (primarily foot-propelled) WEB FOOT diving bird orders, eg. Cormorants (Phalacrocoracidae), Loons (Gaviidae)
Hesperornithidae (Hesperornithes) AND (primarily foot-propelled) LOBE FOOT diving bird orders eg. Grebes (Podicipedidae)
Presbyornithids AND duck, geese and swan (Anseriformes)
Currently these similarities are considered to be due to convergence (evolutionary relay). I am suggesting they are ancestral.
This is something to note:
Cladists decline to identify* the ancestors of these birds (cormorants, loons, grebes, duck, geese and swan). But they are not ruling out that the ancestors may in fact be the ones I just listed. They are just not taking a position on that.
*They decline to identify the ancestors of any and all birds.