Family TYRANNOSAURIDAE

Fig. 5 a, b

Material: Tooth, UCMP 119853 (UCMP-V72207) H 8 mm, W 4 mm .

Discussion: The D-shaped cross section, position of the serrations, and robustness indicate a first right maxillary tooth (Fig. 5 a, b). The D-shaped cross-section gives the tooth an incisiform appearance, and is known only in the premaxillary teeth and first maxillary teeth of tyrannosaurids and in the teeth of Aublysodon mirandus (see below). In all other theropods, the premaxillary teeth become progressively more asymmetrical toward the front of the tooth row as the anterior serrations assume a more medial position (but this does not result in a D-shaped cross section and incisiform tooth; see Lambe, 1917 and Ostrom, 1969). UCMP 119853 is so heavily worn that the anterior serrations are almost obliterated.