There's a fair bit of history on Rocket Raccoon on the various wikis, but none seem to answer one fairly specific question - why is he a raccoon?  [Wikipedia][1] gives an out-of-universe explanation, saying "The character was created by Bill Mantlo and Keith Giffen and consciously inspired by the classic Beatles song "Rocky Raccoon"".  

Is there an in-universe explanation as to why an extraterrestial civilization had a raccoon as their guardian?


  [1]: http://en.wikipedia.org/wiki/Rocket_Raccoon