Meeting Abstract
Teeth are a critical aspect of feeding in most vertebrates and vary greatly in shape and size among taxa. A tooth can perform multiple functions or be specialized for a specific prey type. The tooth plates of Hydrolagus colliei, spotted ratfish (Holocephali), have a narrow occlusal surface and the overall shape of the tooth plate varies within an individual and among species. The occlusal edge varies in the presence and number of sharp points or bumps. Spotted ratfish feed on a variety of hard and soft prey, yet lack the molariform or pavement tooth plates typical of durophagous (feed on hard prey) fish. This study investigated the morphology of the tooth plates of spotted ratfish to quantify the shape variation and describe the material arrangement. Geometric morphometric outline analyses were performed on the tooth plates to evaluate the factors that contribute to shape variation. The principal components that described the majority of shape variation in the tooth plates were the dimension (height or width) and the occlusal edge (smooth vs. pointed). Polarized light microscopy was used to visualize the arrangement of the two materials that form holocephalan tooth plates: hypermineralized dentine arranged as columns of spheres within trabecular dentine. Hypermineralized dentine has a slower wear rate than trabecular dentine, therefore as the relatively softer trabecular dentine wears, leaving the relatively harder spheres as points on the occlusal edge. The spheres eventually wear forming a smooth occlusal edge, after which the cycle starts again. This process is responsible for the variation in tooth plate shape among contralateral elements as well as among individuals and is similar to the self-sharpening teeth of rodents and sea urchins.
