 With the advent of phylogenetic taxonomy in vertebrate paleontology , Tyrannosauridae has been given several explicit definitions . The original was produced by Paul Sereno in 1998 , and included all tyrannosauroids closer to Tyrannosaurus than to either Alectrosaurus , Aublysodon or Nanotyrannus . However , Nanotyrannus is often considered to be a juvenile Tyrannosaurus rex , while Aublysodon is usually regarded as a nomen dubium unsuitable for use in the definition of a clade . Definitions since then have been based on more well @-@ established genera . 
