Albertosaurinae

Holtz, TR jr., 2004, Tyrannosauroidea, The Dinosauria, University of California Press, pp. 111-136 : 3

Albertosaurinae ,

a clade formed by the unnamed Alabama tyrannosaurid and the western North American Gorgosaurus and Albertosaurus , is united by having an antorbital cavity that reaches nasomaxillary suture, the lateral surface of nasal excluded from the antorbital cavity; and a triangular cornual process on the lacrimal, oriented dorsally and placed rostral to the descending ramus of the lacrimal. Currie (2003a) presents data suggesting that albertosaurines have slightly shorter and lower skulls, shorter ilia, longer tibiae, longer metatarsals, and longer toes than tyrannosaurines of the same body size (estimated by femur size); however, the Alabama tyrannosaurid was not included in this analysis, so it is not certain whether these traits are shared by this taxon as well.

The as yet unnamed tyrannosaurid from Alabama is the only confirmed species of this clade from the eastern portion of North America (Carr et al., in press), although Schwimmer (1997), Baird (1989), and Schwimmer et al. (1993) have also described fragmentary tyrannosaurid elements from this region. This taxon is diagnosed by an antorbital fossa deep over the horizontal ramus; a nasal with a row of six midline rugosities (similar to the more pronounced structures in Alioramus ); a wide jugal process of the ectopterygoid, with the caudal pneumatic recess situated rostral to the caudal margin of the vomeropterygoid process; the articular surface of the lacrimal situated dorsally; and a prominent lip extending from the dorsal margin of the articular surface of the pedal unguals. Unlike the present study, Carr et al. (in press) considered this taxon to lie outside of Tyrannosauridae . The Alabama tyrannosaurid is small (having an approximate body length 6 m); however, as this is also a juvenile (Carr et al., in press), it may have reached the size of other albertosaurines.

The two Canadian genera of Albertosaurinae , Gorgosaurus and Albertosaurus , share the following derived characters: the extent of the ventral curvature of the maxilla less than the length of the crown of the largest premaxillary teeth (however, this trait is ontogenetically linked [Carr 1999]; given the nonadult status of the Alabama tyrannosaurid [Carr et al., in press], it may have been present in the adults of the eastern albertosaurine, and as it is present in Tyrannosaurinae , it would thus be basal to Tyrannosauridae as a whole); multiple openings in the lacrimal recess; two foramina on the lateral surface of the palatine; and two foramina leading to the ectopterygoid sinus. Many authors (Russell 1970a; Paul 1988a; Carpenter 1992b; Brochu 2002; Carr and Williamson, in press) consider these two species to be members of the same genus; others (Bakker et al. 1988; Holtz 1994, 2001b; Currie 2000, 2003a, 2003b) retain the original generic names.