I totally missed Corsola in G/S/C, so I thought it was a Gen III Pokémon when I first played those games.
Jumping on the Skarmory train with this one... Interesting that so many people seem to think that xD Others for me were Azurill and Wynaut, somehow in my head gen 3 has all new Pokémon and the baby Pokémon are from gen 2 and 4... but no, these two are from gen 3 XD