King Bowser... Mutated Turtle?

So I was talking to my friend a while ago while I was playing Paper Mario. I was at the 2nd or 3rd act, or whatever it is, when I realized that Bowser was roughly the same color as koopas in the game and has a shell. I'm guessing that koopas are evolved turtles that walk upright... and talk.

I did some research--wikipedia--into what Bowser may be, apparently nobody knows either but according to one of his names in Japanese "King Koopa" it got me thinking that he may be in "reality" a giant koopa, but then I thought, "Weird yo..." because of the fact that he has spikes on his shell and breathes fire.

Are they evolved specimens with the same common ancestor and Bowser is just more evolved than them... or are they, in fact, a completely different species?

...

Sorry, too much Human Origins, now I can't even enjoy video games like this