Albertosaurus older "Gorgosaurus libratus" (sometimes called "Albertosaurus libratus"; see below). These two species are the only described albertosaurines; other undescribed species may exist. Thomas Holtz found "Appalachiosaurus" to be an albertosaurine in 2004, but his more recent unpublished work locates it just outside Tyrannosauridae, in agreement with other authors. The other major subfamily of tyrannosaurids is the Tyrannosaurinae, which includes "Daspletosaurus", "Tarbosaurus" and "Tyrannosaurus". Compared with these robust tyrannosaurines, albertosaurines had slender builds, with proportionately smaller skulls and longer bones of the lower leg (tibia) and feet (metatarsals and phalanges). Below is the cladogram of the Tyrannosauridae based on the phylogenetic
Dianopachysaurus a triangular acetabulum, and a reduced but still quite robust dorsal process. The pubis is round, and has an open obdurator foramen, but the ischium is almost entirely hidden. The femurs are slender and slightly sigmoid, with distinct striations on both ends. They are 14 mm long. The fibulae are slightly longer than the tibiae, at 6.5 rather than 6 mm long. The astragali are larger than the calcanea, but both have flat proximal margins. The first metatarsals are distinctly shorter than the others, and many metatarsals are covered by phalanges and so not fully visible. Enough phalanges are preserved