The Application of Dental Complexity Metrics on Extant Saurians

Abstract: Quantifying morphology has become increasingly popular with the advent of widely available high-powered computing. Orientation patch count rotated (OPCR) is an important measurement of dental surface complexity and has been shown to relate to diet, with carnivores possessing simple teeth and herbivores exhibiting complex dentitions. This method, however, has primarily been applied to mammals with comparatively little research focusing on dentigerous reptiles. Three methods are currently used to measure dental complexity (Surfer Manipulator, molaR, and MorphoTester), and the comparability of these methods remains untested in saurian datasets. Here, we test for differences among the three dental complexity methods using a dataset comprising lepidosaur and crocodylian teeth. Additionally, we seek to test the hypothesis that phenotypic dental complexity is related to dietary ecology using the molaR and MorphoTester OPCR methods. We find that Surfer Manipulator and 3D-OPCR methods (molaR and MorphoTester) generate different complexities, with molaR and MorphoTester consistently producing higher complexity values. The relationship between diet and dental complexity was recovered using molaR and MorphoTester, with carnivores possessing simple teeth and herbivores exhibiting significantly more-complex teeth, but this trend was not as distinct as when using Surfer Manipulator. Dental complexities were highly dependent on model preparation, in particular the triangle count of each 3D model, with surfaces that possess a greater number of faces exhibiting higher complexities. We present a series of recommendations that will help guide future studies of nonmammalian dentitions. Ultimately, 3D-OPCR methods are a fruitful area of research and represent a relatively untapped avenue of quantitative herpetology.