See Early Concept Art from Sonic: Lost World
Below is some concept art that Sega has posted on their blog. Each of the images below also has some notes about the piece of concept art from the development team.
An early development idea which the gears are rotating in different direction. Looks painful if you get sandwiched.
The concept was totally new, so we couldn't decide the direction of the design. It was tough as we had to re-make this first stages over and over.
Head over to Pure Nintendo to check out the rest of the images.