When I first saw the movie, I just assumed he was a fat human pirate. But, I just saw this again on Toon Disney and got a better look and saw he had pointed ears and claws. So, I'm guessing he's a cat-alien like Amelia?
It says somewhere that his species is called something with urs. I'm not entirely sure that the source in question is reliable, anyway I still believe he's supposed to be a bear-like alien. So the poster above me is probably right. When I first started to think about what he was, I thought he might be a rat. The fact that Sven Wollter, the Swedish voice actor, played a rat in a tv show, might have helped :) Your guess isn't dumb at all though, nobodyriku, because they do have some physical traits in common.