SUBGENUS TYRANNOSAURUS (DASPLETOSAURUS) (Russell, 1970)

TYRANNOSAURUS (DASPLETOSAURUS) TOROSUS (Russell, 1970)

synonym — Albertosaurus libratus

TYPE, BEST AND DISPLAY SPECIMEN— NMC 8506

time—late Campanian of the late Late Cretaceous

horizon and distribution—Judith River Formation of Alberta

Until recently, this species’ remains were lumped in with A. libratus of the same formation. But even as he dug up the first good skull and skeleton in 1921, Sternberg suggested that it was a new taxa, and Dale Russell made it the type of the evocatively titled Daspletosaurus torosus . However, as explained above, this species belongs in Tyrannosaurus, of which it is the earliest. No complete skeleton is known, but Russell combined the skull and partial skeleton of the type with the hind limbs of equal-sized AMNH 5436 and restored a few parts to make a very good restoration, one that has been modified here. Philip Currie has a hefty new preorbital horn that may come from a somewhat larger example of this species As well as being smaller than those of the other genus members, the skull has bigger openings and lacks the bar that nearly cuts the orbit in two. On the other hand the skull is quite big for the body. The best skull of the species, ROM 8506, is crushed from side to side and obscures the fact that T. torosus had a good degree of binocular vision. The moderate-sized preorbital horn is triangular; the forelimbs are the biggest known in an advanced tyrannosaur. Russell has explained that since T. torosus is more robust than, and one fourth as numerous as similar-sized A. libratus, it probably went after the relatively less common and powerful horned dinosaurs more often than the albertosaur did.