[ShadowAce]

Of course, perhaps those better adapted for movement on the surface later ...

Why would a fish be adapted for movement on the surface?

[Dimensio]

Why would a fish be adapted for movement on the surface?

Mutation.

[Physicist]

Why would a fish be adapted for movement on the surface?

The current thinking is that the proto-amphibians adapted fins into limbs because it enabled them to wriggle through dense aquatic vegetation more easily. That the limbs enabled them to move clumsily about on land was fortuitous.