Tyrannosaurus rex possesses a heterodont dentition composed of three classes (premaxillary, maxillary, and dentary) and several sets. The maxilla contains mesial and distal sets and the dentary contains first dentary tooth (d1), mesial, and distal sets. Teeth were described with four size and two shape variables and several variables describing crown curvature and denticle size. The premaxillary teeth are derived structures with labiolingually oriented long axes, moderate mesial curvature, and mesiolingually and distolingually placed carinae that extend down the lingual faces. The mesial maxillary crowns are large, basally rounded, and moderately curved with mesiodistally oriented long axes. The mesial carinae begin at the apices and curve lingually to about the midcrown point and the distal carinae begin at the apices and extend down the labial sides of the distal faces. The distal maxillary crowns are larger than the premaxillary and smaller than the mesial maxillary and all but the most distal dentary teeth. They have labiolingually oriented long axes and have narrower basal widths than lengths. The carinae roughly define the mesiodistal axes of the crowns. The first dentary tooth is similar to those of the premaxilla. The mesial dentary teeth are similar to the mesial maxillary teeth and the distal dentary teeth are similar to those in the distal maxilla. This examination revealed that several putative systematic characters related to size and shape can be discerned from T. rex teeth, suggesting that useful dental characters may be more common within the Theropoda than has generally been presumed.
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