What is it about the physics of being underwater that would allow relatively large, sometimes highly mobile creatures to flourish that isn’t true for boneless land creatures?

As scientists have investigated evolution from a variety of fields, they have found that some of darwin's orginal ideas were inaccurate or incomplete. t explanation provided by evolution was updated each time to reflect the new information they found. what does this suggest about the theory of evolution? it has become a stronger and clearer theory as new information is collected.