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 Thomas Holtz found "Appalachiosaurus" to be an albertosaurine in 2004, but his more recent unpublished work locates it just outside Tyrannosauridae, in agreement with other authors.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
Vancleavea parts of the hand. The second metacarpal is longer, and the third and fourth are tied for the longest bones of the hand. Unguals (claws) have not been found, and the rounded ends of certain phalanges indicates that "Vancleavea" likely did not possess them. As with other reptiles, each hip of "Vancleavea" is formed by three plate-like bones: the illium (above the hip socket), the pubis (in front of the hip socket), and the ischium (behind the hip socket). The illium of "Vancleavea" is particularly unusual. Most archosauriforms have illia which are somewhat low, directed from front to back (anteroposteriorly).