maybe it's because whales just blob about on the surface not doing much
but elephants are actively swimming so need much faster gas exchange
( glued eel /questions/questionsyoudliketoask/post1648081, Tue 30 Jun 2009, 14:18, archived)

I guess whales only breathe when they come up,
not while they're swimming along.

Imagine a whale with a big trunk though, that would be awesome.
( Moon Girl Technologies horrendous beanbag, Tue 30 Jun 2009, 14:26, archived)