Even though the differences appear superficially striking, they do not involve any novel body plans (i.e., no new proteins, new tissues, or new organs).
That evolution, over a span of 11 million years or so, was once hailed as a “poster child” for the confirmation of Darwinian theory.
Whales are held up as a model of what unguided evolution can do in a short time: in this case, just 8 million years, or perhaps even half that.
There are a few problems with conventional accounts of whale evolution. Together they’re a killer.