Petrie's Imaginary Friend is an imaginary Sharptooth with no teeth that only exists in Petrie's imagination. He is believed by some to be a stylistic depiction of Tyrannosaurus, though he lacks teeth and is comically designed.
He is short, deep-green and yellow, with pink spots here and there. The Sharptooth has a pigeon-toed stance, and a crest on his head. He also later grew wings. He appears only in the The Land Before Time IX: Journey to Big Water. The first appearance is during the song "Imaginary Friend" and again later while Petrie is flying alone. It is at this time that Petrie imagines him with wings on him so he can fly while Petrie is flying alone. It is not known if just Petrie has an imaginary friend or if other flyers may since they can be flying alone for periods of time. Since Petrie didn't find it odd to have an imaginary friend, and the other members of the gang didn't seem to know about him having one, it can be said that the subject has not come up before, and it is a seldom talked about thing within the Great Valley, or at least the gang.