Mammoths!... Nvm.
Giants! Toolate.
Really though, more unique creatures, Scribs, Shalks, Kagouti's, Alits, and yes, even the Cliff Racers, added a sense of foreign atmosphere to Morrowind that was really lacking in Oblivion. I mean, We've all seen Minotaurs, Trolls and whatnot, I want some really unique Fauna. I wouldn't count Daedra among them, since things like Scamps, Dremora, Golden Saints, ect are more akin to demons than animals.
Did Oblivion even have any Game-unique animals? I mean, even the Mudrabs were no bigger than what you see on the Discovery Channel now. Still, their pincers are sharp.