Of course, now, we know they probably had as much similarity to lizards as we do.

Another interesting thought experiment is an octopus civilization. They are probably smart enough to have also developed along those lines.

Depending on what that civilization would have looked like, there might not be much left.

I remember reading an essay (probably linked from here), that it might only take a couple of million years, to completely wipe all traces of even an advanced, mechanized civilization. They posited that the only evidence of our civilization, in a few million years, would be marbles.