Dumbo rats don't have humongous ears, they just look larger because they are rounder and set on either side of the head. There is a bigger difference between Dumbos that are being carefully bred by Breeders and the willy-nilly breeding of pet store Dumbos. read more
The only real difference between Dumbo rats and standard rats are the ears (Dumbo and standard - or 'top ear' if you prefer - are the terms, 'fancy rat' is just the term for domestic pet rats.) Their ears are bigger/rounder and sit a wee bit lower on their heads. read more