Tarbosaurus bataar Maleev, 1955

Christopher A. Brochu, 2003, Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull, Journal of Vertebrate Paleontology 22, pp. 1-138 : 4

Tarbosaurus bataar Maleev, 1955

—This is the best-known non-North American tyrannosaurid, and is known from multiple skeletons from the Nemegt Formation of Mongolia ( Maleev, 1955, 1974). Most recent estimates place the Nemegt in the Early Maastrichtian. Isolated tyrannosaurid fragments from several Maastrichtian localities in Mongolia and China have been referred to Tarbosaurus (Molnar et al., 1990) , but all consideration in this study refers to the Nemegt tyrannosaurid.

In its first description, Tarbosaurus was called Tyrannosaurus bataar ( Maleev, 1955) . Tarbosaurus was later erected for a smaller skeleton from the same unit ( Tarbosaurus efremovi), and the two were later regarded as synonymous, with Tarbosaurus being used as the generic name (Maleev, 1974). Maleev’s extensive posthumous descriptive work on this animal (1974) applied the name efremovi, even though bataar has priority. Maleev also described several small tyrannosaurid skeletons, including two he referred to Gorgosaurus (G. lancinator and G. novojilovi, later referred by Carpenter [1992] to the new genus Maleevosaurus ), but these are now regarded as earlier immature specimens of T. bataar ( Carr, 1999) . The smallestknown tyrannosaurid skeleton, the type of Shanshanosaurus houyanshanensis Dong, 1992 from western China, may also be an immature example of Tarbosaurus (Currie and Dong, 2001a) . All specimens of Tarbosaurus examined in this study were mature, and comments will be restricted to them.

This animal is today frequently called Tyrannosaurus bataar (e.g., Paul, 1988; Carpenter, 1992; Holtz, 1997, 2001a; Carr, 1999), and similarities between the two large Maastrichtian tyrannosaurids are striking. Both have similar postorbital protuberances, and in both the lacrymal “horn” is barely a protuberance at all. Tarbosaurus has more maxillary and dentary alveoli at maturity (13 maxillary alveoli in T. bataar , as opposed to 12 in T. rex ), but the number of alveoli is smaller in these two than in other mature tyrannosaurids. A close relationship has been presumed in the past ( Fig. 1 ), a conclusion supported by Holtz’ (1997, 2001a) phylogenetic analyses.

Figures

FIGURE 1. Phylogenetic relationships among theropods and (inset) within Tyrannosauridae as applied herein. Theropod phylogeny based largely on Sereno (1997, 2001) and Norell et al. (2001); uncertain placement of Herrerasauridae reflects information from Langer (2001), and unresolved “Ceratosauria” is based on Carrano and Sampson (1999). Tyrannosauroid phylogeny based on Currie (2000) and Holtz (2001a).