if dolphins are mammals why are they not adapted to live on land like most other mammals?

Question: if dolphins are mammals why are they not adapted to live on land like most other mammals?
- Keywords:
  adaptation,
  dolphin,
  evolution,
  land,
  mammal
Asked by summss to Charlotte, Jo, Kevin, Louise, Valeria on 18 Jun 2012.
- Valeria Senigaglia answered on 18 Jun 2012:
  
  Dolphins evolved from a terrestrial animal but then adapted to live in the water..maybe at the time the land was too crowded so they explored new environments
- Joanna Cruden answered on 18 Jun 2012:
  
  The sea takes up a greater surface of the earth than land so maybe it just makes more sense to stay there

Question: if dolphins are mammals why are they not adapted to live on land like most other mammals?