Pattern and process of serrations and denticles of reptilian teeth

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Size and shape of the serrations are often used as a diagnostic character in the theropod dinosaurs. There are very few studies of intraspecific variations of these characters. It is largely because there is not an appropriate method to describe the variations and to test them statistically. This study was to create digital image database for intraspecific variations and it was also to explore a suitable morphometric method. Two species of extant reptiles, Varanus and Iguana, and one species of an extinct reptile, Velociraptor, were chosen to measure tooth crown basal length, width, height, and serration or denticle basal length. Varanus was chosen because it is considered as one of the best analogues for theropod dinosaurs. Iguana was measured to made a comparison of its denticles to the serrations of Varanus. Velociraptor, a thropod dinosaur, was measured because it has a derived character in the serrations. Variations of serrations/denticles were the greatest among the four measurements taken in all the three species. A functional tooth in use shows differences in serration/denticle basal length from a replacement tooth in the same tooth position. The Velociraptor specimen did not show a derived character state. These findings strongly suggest that one should exercise caution on the use of characters on serrations and/or denticles. Several morphometric analyses were attempted to describe variations in dental characters. Due to high variations observed in serrations/denticles, morphometric methods turned out to be not suitable for the description.