 Later in the same paper he proposed that Tyrannosauridae be defined as "all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon." He also criticized definitions previously proposed by other workers, like one proposed by Paul Sereno, that the Tyrannosauridae was "all taxa closer to" Tyrannosaurus "than to Alectrosaurus, Aublysodon, and Nanotyrannus." Holtz observed that since Nanotyrannus was probably a misidentified T. rex juvenile, Sereno's proposed definition would have the family Tyrannosauridae as a subtaxon of the genus Tyrannosaurus. Further, his proposed definition of the subfamily Tyrannosaurinae would also be limited to Tyrannosaurus.
