Super Mario Kart has a lot of firsts. It's the first game in the Mario Kart series, the first kart racing game, and the first in the mascot racing genre. But with all these firsts come a lot of developmental changes, lucky for us. And thanks to the discovered prototype of Super Mario Kart, we'll be able to see these changes too.
Enjoy!
Sources:
More info on music changes: http://www.nintendoplayer.com/prototype/super-mario-kart/
DK Jr. Beta Victory Theme: https://youtu.be/6jQQbFxXXDA
Vanilla Lake Beta Theme: https://youtu.be/lK-PG98e2t4
Others:
http://snescentral.com/review.php?id=0166&num=1&fancy=yes&article=proto
http://snescentral.com/article.php?id=0874
http://tcrf.net/Super_Mario_Kart
https://en.wikipedia.org/wiki/Super_Mario_Kart
https://www.unseen64.net/2008/09/23/super-mario-kart-snes-beta-proto/
http://www.mariowiki.com/List_of_Super_Mario_Kart_pre-release_and_unused_content