I'm not quite sure what they are, but with the horrible inconsistent animations, and considering the fact that the Rainbow Faces were aliens, they might as well not be classified as any specific species of dinosaur. They probably chose a form that both suited their needs (ex., needed to have dexterous hands in order to manipulate objects, strong arms in order to push and pull and things if necessary, and powerful legs to move about easily) and fitted in with the resident dinosaurs.