Scientists have commonly understood Tyrannosauroidea to include the tyrannosaurids and their immediate ancestors. With the advent of phylogenetic taxonomy in vertebrate paleontology, however, the clade has received several more explicit definitions. The first was by Paul Sereno in 1998, where Tyrannosauroidea was defined as a stem-based taxon including all species sharing a more recent common ancestor with "Tyrannosaurus rex" than with neornithean birds. To make the family more exclusive, Thomas Holtz redefined it in 2004 to include all species more closely related to "Tyrannosaurus rex" than to "Ornithomimus velox", "Deinonychus antirrhopus" or "Allosaurus fragilis". Sereno published a new definition in 2005, using "Ornithomimus edmontonicus", "Velociraptor mongoliensis" and "Troodon formosus" as external specifiers. The Sereno definition was adopted in a 2010 review.