"Pluto is unusual for a Disney character in that he is not anthropomorphized beyond showing an unusually broad range of facial ex<x>pressions or use of his front paws at key points; he is actually represented as a normal dog (unlike Goofy who is an anthropomorphic dog)." (en.wikipedia.org/wiki/Pluto_(Disney))
Different species. Dog of Martian in Bugs Bunny was on all fours too.<br />
Brian Griffin does both. No suprise eh?
Goofy is the house dog and Pluto is the field dog