DENTAL MORPHOLOGY AND VARIATION IN THEROPODS: IMPLICATIONS FOR THE IDENTIFICATION OF SHED TEETH

Isolated theropod dinosaur teeth occur frequently in Upper Mesozoic rocks and confident taxonomic identifications of these elements are desirable. However, a lack of clear qualitative tooth characters has confounded efforts to correlate isolated teeth with established genera and the few quantitative studies that have been done were based on isolated teeth whose taxonomic affinities were assumed. As such, an understanding of the taxonomic utility of theropod teeth remains elusive. This study attempted to rectify the problem by starting to create a standard dataset based on theropod teeth of known taxonomic affinity (teeth within jaws) against which isolated teeth could be compared. Tooth morphology was described using a number of existing and new size variables referring to total crown length, base length and width, and denticle size and newly derived shape variables referring to basal shape, squatness, mesial curve shape, and apex location with respect to crown base. Crown curves were described by fitting the square root function Y = a + bX^0.5 to X, Y coordinate data collected from digital images of mesial curve profiles of teeth photographed in lateral view (data were normalized to 1 by dividing the set by the range of x values). The b value generated from this analysis provides a measure of crown curvature and can be examined on its own or with other variables. Statistical tests such as Principal Components Analysis and Discriminant Function Analysis were used to compare a number of theropod dentitions and compare isolated teeth of various presumed taxonomic affinities against the standard. These methods permitted the discrimination of morphologically similar teeth (e.g., Daspletosaurus from Tyrannosaurus; Dromaeosaurus from Deinonychus) and successful identification of cf. Tyrannosaurus teeth as Tyrannosaurus, suggesting that expanding the standard should facilitate the identification of numerous types of isolated theropod teeth.