You know i learned something very obvious when i was on holiday in the Dominican Republic this year at Ocean world. Whales, Dolphins and Seals when 'swimming' theirs 'tails' go in an up and down motion, however fish tails swish from side to side. Another obvious evolutionary trait where by the legs of their ancestors 'fused' together.

Look at your own legs and imagine how you would swim if your legs were bound. Obvious really when you look at it.

yes that is a good observation, even though I've known this for a while.