>1. They are very large (i.e. hippos), or > >2. they swim very, very well (i.e. otters), or > >3. they can get out of the water in a real hurry (i.e. ducks). >
Put when the ancestral animal first crawled into the sea that would give
rise to the seal species we have today, I very much doubt it had any of
these three features either. And it survived.