Quantification of carinar process plate orientation in camarodont sea urchin teeth

Most sea urchins (Echinodermata: Echinoidea) possess a feeding apparatus complete with five teeth. Sea urchin teeth are highly complex, three-dimensional (3D), calcite structures consisting of needle-prisms and plates (primary, secondary, as well as carinar process plates in some taxa). The 3D structure of tooth plates is of interest both from a phylogenic as well as a biomechanical point of view. Synchrotron microComputed Tomography was used to quantify carinar process plate morphology in teeth of two camarodonts (Echinoidea: Camarodonta), Gracilechinus affinis (Mortensen, 1903) (Echinidae) and Toxopneustes roseus (Agassiz, 1863) (Toxopneustidae). A third species, Temnopleurus toreumaticus (Leske, 1778) (Temnopleuridae) was investigated qualitatively. Imaging focused on the tooth shaft, just adoral of where the keel first reaches its maximum extent. Carinar process plates curve significantly, and this curvature may prevent shear between adjacent plates. Therefore, the type and amount of nonplanarity in carinar process plates were investigated numerically. The 3D coordinates of the center of each plate were measured for a matrix of positions spanning the plate, and these coordinates were used to calculate the local angles the plates make with respect to the slice plane. The distribution of carinar process plate angles is reported along with the mean and the ranges of angles for the two camarodont species. The report concludes with a discussion of application of this quantitative approach to carinar process plates of other taxa as well as other tooth structures such as prisms.