I don't know if I'd agree that removing Shorty would make anything more believable. I think it would just stay the same level of believability. True, Chomper kind of fills the "brother" thing for Littlefoot, but since when did someone need only "one sibling"? What's wrong with another one? Plus, Shorty is a longneck, the same species as Littlefoot, whereas Chomper is a sharptooth. Not saying befriending a sharptooth is bad; I like that aspect of their relationship, being able to get along despite being on the opposite end of the food chain. But don't you think Littlefoot would enjoy having a brother, of sorts, who is the same species as him? Especially considering, out of all the friends he made, only 3 are longnecks (yes I'm counting Rhett), and all of them are away most of the time.