Variation in Premaxillary Tooth Count and a Developmental Abnormality in a Tyrannosaurid Dinosaur

Abstract

Premaxillary tooth count tends to be stable amongst toothed dinosaurs, and most theropods have four teeth in each premaxilla. Only one case of bilaterally asymmetric variation is known in theropod premaxillary dentition, and there is no record of ontogenetic or individual variation in premaxillary tooth count. Based on these observations, a tyrannosaurid left premaxilla with three teeth (TMP 2007.20.124) is an interesting deviation and represents an unusual individual of Daspletosaurus sp. with a developmental abnormality. The lower number of teeth is coupled with relatively larger alveoli, each of which is capable of hosting a larger than normal tooth. This indicates that tooth size and dental count vary inversely, and instances of reduction in tooth count may arise from selection for increased tooth size. On the other hand, the conservative number of premaxillary teeth in most theropods implies strong developmental constraints and a functional trade-off between the dimensions of the premaxillary alveola...