Dental Complexity and Crown Relief Document Occlusal Wear Along the Tooth Row in West Indian Manatees

ABSTRACT

Sirenians are a lineage of herbivorous marine mammals morphologically specialized for exploiting aquatic vegetation in shallow‐water habitats. In manatees ( Trichechus ), continuous horizontal tooth replacement may represent a solution for mitigating heavy dental wear incurred by a diet of abrasive plant material. In this study, we examine patterns of dental wear in manatees by quantifying two properties of the occlusal surface across the dental arcade. We used orientation patch count, rotated (OPCR) to measure surface complexity and relief index (RFI) to measure surface relief, in high‐resolution 3D tooth models from scanned skulls of Trichechus manatus ( N  = 8 individuals). Both measures declined toward the anterior of the tooth row, consistent with the accumulation of wear as teeth migrate forward. Relief declined more steeply than complexity, and did so nonlinearly, changing little across the four anteriormost positions. Maxillary teeth were more complex but lower in relief than mandibular teeth, indicating that complexity and relief are sensitive to different aspects of wear. Between‐specimen differences explained most of the variation in complexity but less of the variation in relief. Our results suggest that OPCR and RFI provide complementary measures of dental wear, and that wear accumulates measurably along the tooth row in manatees.