Tyrannosauridae, Osborn, 1905

Holtz, TR jr., 2004, Tyrannosauroidea, The Dinosauria, University of California Press, pp. 111-136 : 7

Within Tyrannosauroidea, Tyrannosauridae

has been phylogenetically defined, although this definition has been rendered problematic owing to the nature of some of the putative terminal taxa (Brochu 2002). Sereno (1998) defined this taxon as all tyrannosauroids closer to Tyrannosaurus than to Alectrosaurus , Aublysodon , or Nanotyrannus , and Holtz (2001b) defined it as all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon . However, Aublysodon is based on indeterminate (and lost) material, and the derived feature previously claimed for it—the lack of serrations on the teeth—may be due to postmortem damage rather than actual anatomy (Brochu 2002; Carr and Williamson, in press). Furthermore, Nanotyrannus lancensis is likely a juvenile Tyrannosaurus rex (Carr 1999; Holtz 2001b; Brochu 2002; Carr and Williamson, in press); and even if it is not, it is almost certainly from a taxon more closely related to T. rex than to all other taxa previously regarded as tyrannosaurids (Holtz 2001b; Currie 2003b). Finally, Alectrosaurus may be a nomen dubium (Carr et al., in press), and due to its incompleteness it is phylogenetically labile (Currie 2003b).

Here, Tyrannosauridae is defined as comprising Tyrannosaurus rex , Tarbosaurus bataar , Daspletosaurus torosus , Albertosaurus sarcophagus , Gorgosaurus libratus , their most recent common ancestor, and all of its descendants. Furthermore, two subclades can be defined: Tyrannosaurinae , a stem-based taxon composed of Tyrannosaurus rex and all taxa sharing a more recent common ancestor with it than with Albertosaurus sarcophagus ; and Albertosaurinae , a stem-based taxon composed of A. sarcophagus and all taxa sharing a more recent common ancestor with it than with T. rex .

The precise position of Tyrannosauridae , and by implication of Tyrannosauroidea, within Coelurosauria is uncertain. Maniraptoriformes was defined (Holtz 1996a) as all descendants of the most recent common ancestor of Ornithomimus and modern birds. Arctometatarsalia comprises those taxa closer to Ornithomimus than to modern birds, while Ornithomimus comprises those closer to modern birds than to Maniraptora (Holtz 2001a). The three main hypotheses of tyrannosaurid relationships within Coelurosauria are (1) Tyrannosauridae is a coelurosaurian clade outside Maniraptoriformes (Pérez-Moreno et al. 1994; Forster et al. 1998; Makovicky and Sues 1998; Norell et al. 2000; Rauhut 2003); (2) Tyrannosauridae lies within Arctometatarsalia (Pérez-Moreno et al. 1993; Holtz 1994, 1998a, 2001a); and (3) Tyrannosauridae lies within Maniraptora (Sereno 1999a). Novas (1992b) and Wagner and Gauthier (1999) presented Tyrannosauridae as one branch of an unresolved tritomy with Ornithomimosauria and Maniraptora; this would also be the strict consensus of the three hypotheses presented above.

The phylogenetic analysis presented here is the same as that presented in Holtz et al. (this vol.). This analysis comprises 76 taxa (with Herrerasauridae as an outgroup) and 638 morphological characters. DELTRAN optimization was selected for purposes of discussing the distribution of derived character states. See Holtz et al. (this vol.) for more details of the methodology and the structure of the most parsimonious trees beyond the portion examined here.

Figure 5.22 represents the Tyrannosauroidea portion of the 2,5 4 4 most parsimonious trees. These trees have a length of 2,444, CI = 0.354, RI = 0.715, RCI = 0.253, and HI = 0.662. In this analysis Tyrannosauroidea was found to lie outside of the Maniraptora-Ornithomimosauria clade Maniraptoriformes, but it was united with these taxa above the Compsognathidae in a clade that meets Sereno’s (1999a) definition of Tyrannoraptora (i.e., Tyrannosaurus , modern birds, their most recent common ancestor, and all of its descendants).

The taxa within Tyrannosauroidea are discussed here from more basal forms to those higher on the tree.