 Gorgosaurus is classified in the theropod subfamily Albertosaurinae within the family Tyrannosauridae . It is most closely related to the slightly younger Albertosaurus . These are the only two definite albertosaurine genera that have been described , although other undescribed species may exist . Appalachiosaurus was described as a basal tyrannosauroid just outside Tyrannosauridae , although American paleontologist Thomas Holtz published a phylogenetic analysis in 2004 which indicated it was an albertosaurine . More recent , unpublished work by Holtz agrees with the original assessment . All other tyrannosaurid genera , including Daspletosaurus , Tarbosaurus and Tyrannosaurus , are classified in the subfamily Tyrannosaurinae . Compared to the tyrannosaurines , albertosaurines had slender builds , with proportionately smaller , lower skulls and longer bones of the lower leg ( tibia ) and feet ( metatarsals and phalanges ) . 
