Why cant these simply be varieties of whale...or some other type of marine animal?
You seem to have a thing about common names. A transitional fossil is in actuality, any fossil since it is transitional between it's parents & its offspring. Bringing this out over a long period the changes do to mutations, & the natural selection of such alter the organisms. The fact that, as you say "all of three," there only needs to be 1 to show the relationship. As for what they are, that is the the point. They are transitional and could theoretically be classified as either the previous or post grouping depending on how much difference there is. As for returning to the sea, whales weren't the first. It has occurred several other times, turtles, snakes, pleisosaurs & ichthiosaurs.
There is no better love between 2 people than mutual respect for each other WT Young, 2002
Who gave anyone the authority to call me an authority on anything. WT Young, 1969
Since Evolution is only ~90% correct it should be thrown out and replaced by Creation which has even a lower % of correctness. W T Young, 2008