Eotyrannus

Holtz, TR jr., 2004, Tyrannosauroidea, The Dinosauria, University of California Press, pp. 111-136 : 8

Eotyrannus

and Tyrannosauridae are united by several derived features, including a premaxillary tooth row arcade oriented more transversely than rostrocaudally; nasals fused and their dorsal surface rugose; D- or U-shaped premaxillary teeth with both carinae placed along the same plane perpendicular to the long axis of the skull; premaxillary teeth much smaller than maxillary teeth; pleurocoelous caudal dorsal vertebrae; the humeral ends little expanded; and the ulna facet for the radius transversely expanded and concave (also in some maniraptorans). Premaxillary teeth with a D- or U-shaped cross section are found in the Late Jurassic of North America (Bakker 1998a, 1998b) and Europe (Zinke 1998; Rauhut 2000b), the Early Cretaceous of Japan (Manabe 1 999), and the base of the Late Cretaceous in western North America (Cifelli et al. 1997a; Kirkland et al. 1997). These authors have generally referred these specimens to Tyrannosauridae or, if serrations were not preserved on the carinae, to Aublysodon ; however, the new information from Eotyrannus demonstrates the presence of this tooth form in nontyrannosaurid tyrannosauroids.