What's that red thing on Yoshi's back?

The red thing on Yoshi's back was originally a saddle, thus it being flat and fabric-looking in his first several debuts. For some reason it has gotten bumpy and round in appearance, but I assure you it is not a shell, it is indeed a saddle. For starters, why would they change it from a saddle to a shell and NOT give an explanation anywhere? It also has no markings like every other shell in the Mario games, and makes no sense for it to be a shell. Yoshi was a dinosaur with a saddle when he started, and that's what he still it.

For all of you out there who insist it is a shell and that Yoshi is a turtle, you really do need to play the old Mario games...