In this proposed classification system, the tyrannosauroids were supposedly basal to a clade known as Bullatosauria, which was made up of the Troodontidae and the Ornithomimosauria. These two groups were purported to form a clade, because they both shared a common characteristic; which was a skull capsule. However, later on, both of these classification systems were found to be paraphyletic, or "artificial", clades.
This proposed classification system was based on the idea that tyrannosauroids were basal to Bullatosauria, which included Troodontidae and Ornithomimosauria. However, this classification was found to be paraphyletic or artificial because it did not include all descendants of a common ancestor.