Abstract

Five sources of variation in dinosaur teeth – positional, ontogenetic, intraspecific, taxonomic, and chimeric – are rarely analyzed in sufficient detail to justify using dental characters to define a taxon. Palaeoscincus costatus is a nomen dubium because the single holotype tooth falls within the range of variation in teeth of two species that can be distinguished by nondental characters. Two specimens of Ankylosaurus have teeth subtly different from the holotype of A. magniventris, but the range of variation is incompletely documented, and dental characters are inadequate to establish a second species.

Introduction

Isolated dinosaur teeth have been made the types of several familiar taxa (e.g., Iguanodon mantelli, Palaeoscincus costatus, Trachodon mirabilis, Troodon formosus). The maintenance of old taxa based on isolated teeth and the temptation to define new taxa using only subtle differences in single teeth continue without regard to the variability present in dinosaur teeth. This paper explores potential sources of variation in teeth of two ankylosaurs: Palaeoscincus costatus, an old taxon based on an isolated tooth, and Ankylosaurus magniventris, the three known skulls of which have teeth of slightly different morphology.

Sources of tooth variability

There are five possible sources of variation in tooth morphology: positional, ontogenetic, intraspecific, taxonomic, and chimeric. Positional variation encompasses changes in teeth along a dental row, including size, number of cusps, and ornamentation (grooves, ridges, serrations, and other irregularities on the enamel).