Maybe the manuscript picture (above) is actually a more accurate personification, after all, didn't he live in a swampy area on Dagobah? Could explain the flippers. Maybe they are simply retractable webbing between fingers?
I don't think it was ever disclosed just where Yoda came from originally or what species he was?
Life-Size Yoda Giveaway
Nah, go ahead, and let the force decide, always it does!