Shigeru Miyamoto had expressed that he wanted Mario to ride on an animal since Super Mario Bros. was finished. This wasn't possible, though, since the NES technical limits wouldn't allow it. Of course, this was changed with the debut of the Super Nintendo Enterainment System, which helped them bring Yoshi to life in Super Mario World.
Yoshi is likely modeled after Tamagon, who is the protagonist of Devil World, another of Nintendo's games. Takashi Tezuka mentioned that Yoshi was going to originally be a Koopa, with the saddle being a shell. His appearance has also gone through a number of changes over the years, with his initial form resembling an actual dinosaur and then having his arms get longer, as well as other aesthetic changes.
