Daspletosaurus torosus Russell 1970

Carpenter, K., 1992, Tyrannosaurids (Dinosauria) of Asia and North America, Aspects of Nonmarine Cretaceous Geology, Beijing: China Ocean Press, pp. 250-268 : 260-261

Daspletosaurus torosus Russell 1970

Figs. 2G , 5F

Holotype: NMC 8506 ,skeleton lacking hind legs from the Judith River Formation of Alberta .

Diagnosis: (Cranial) Premaxilla does not contact nasals under external nares; lacrymal horn well developed; postorbital rugose, although less that Tyrannosaurus ; pro-maxillary fenestra very small; surangular foramen very large. (Postcranial) Postacetabular blade of ilium very long; ischium straight; scapula broadens gradually posteriorly; acromion process of scapula forms a continuous arc with the coracoid.

Stratigraphic and Palaeobiogeographic Distribution: Judith River and Horseshoe Canyon formations of Alberta,Canada;Judith River Formation of Montana.

Discussion: As Russell (1970) has pointed out, adult Daspletosaurus the same length as an adult Albertosaurus is heavier and more powerfully built. This gives it the appearance of Tyrannosaurus , but this resemblance is superficial. Numerous differences between the two animals, such as the lack of the postorbital extending into the orbit and no contact between the nasal and premaxilla below the external nares, indicate that Daspletosaurus is distinct from Tyrannosaurus (see also Russell, 1970).

As yet, Daspletosaurus is too poorly represented with skulls and skeletons to determine the full range of variation, including individual, sexual and ontogenetic. The largest individual (CM 9401)is represented by a nearly complete right lacrymal larger than that of the holotype of T. rex (CM 9380). This is suggests a skull with a premaxillary-occipital condyle length of over 1200 mm. A detailed osteology of Daspletosaurus is in preparation.

Figures

Figure 2. Comparison of tyrannosaurid skulls: A-Tyrannosaurus rex AMNH 5027 (modified from Osborn, 1912); B-Tyrannosaurus bataar holotype PIN 551-1, with missing areas restored after PIN 551-3 and GI SPS 100/59 (from photographs,Maleev, 1974 and Barsbold,1983);C-Maleevosaurus novojilovi holotype PIN 552-2 (modified from Maleev, 1974);D-Albertosaurus sarcophagus AMNH 5222, with lower jaws based on NMC 5600 and NMC 5601 (modified from photographs and Lambe, 1904);E-Albertosaurus libratus(modified from Russell, 1970); F-? Albertosaurus lancensis holotype CMNH 7541, composite of the left and right side (modified from photographs);G-Daspletosaurus torosus(modified from Russell, 1970 and photographs of NMC 8506). All drawn to scale;scale beneath Tyrannosaurus rex = 10 cm .

Figure 5. Comparison of tyrannosaurid skeletons: A-Tyrannosaurus rex(based on drawings and photographs of AMNH 5027 and CM 9380);B-Tyrannosaurus bataar (based on photographs of PIN 552-1,a young adult);C- Maleevosaurus novojilovi (modified from Maleev, 1974);D-Albertosaurus sarcophagus (skeleton based on photographs and drawings of ROM 807,with the skull based on photographs and drawings of AMNH 5222,NMC 5600 and NMC 5601); E- Albertosaurus libratus (skeleton modified from Lambe, 1914,and skull modified from Russell, 1970);F-Daspletosaurus torosus (modified from Russell, 1970). All drawn to scale;height of scale beneath Tyrannosaurus rex tail = 1 m .