You should get a copy of 'The Treatise of Vertebrate Paleontology"
and compare the skeletal and skull configurations of the ear and nares from paleocoetus through to the various species of modern whales. Its worth a convincing look see for yourself. If youre a student you can then raise some questions of how these animals retain the basic features during their evolution but these various features serve entirely new purposes.
Too bad we dont have the genes of the paleocoetus or amblyocoetus, wed be able to look at the genes that are turned "off" or "on" and where new genes occur.