The standing position saw fewer changes than the running one, at least between the first and second games. Left to Right: Sonic 1, 2, 3 and Sonic Spinball - MD/Gen
Hedgehogs are known for their unusual gait, but this might have been too unusual for Sega: Sonic's feet were snapped into place fron the second game onwards. The feet on the first generation Sonic tended to orient the soles inward. If you look carefully you can see how Sonic's running skills have straightened out his feet too. Sonic's shoes, perversely, seemed to get cleaner as time went on - by the third game they were gleaming, and they seemed to be much rounder. The first Sonic had very skinny arms and legs, but by Sonic 3 they were quite a bit more muscular in appearance. There was a steady progression in Sonic's limbs. Sonic was initially a less vivid shade of blue, something that changed in Sonic 2 to help Sonic stand out against the background, and stayed that way for the rest of the series.
The Sonic sprites below show a clear progression, and it's easy to see how Sega's artists refined their mascot's image. There were only five Sonic games on the MegaDrive, ignoring games that re-used sprites (Sonic & Knuckles, Knuckles' Chaotix & Sonic CD).
