THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS OF EXTINCT SHARK TEETH

Due to the nature of the fossil record, little is known about function or diet of ancient sharks. These aspects are usually inferred from a combination of qualitative dentition characteristics and contemporaneous prey items. The goal of this study is to quantitatively explore the link between form and function for fossil shark teeth using Finite Element Analysis (FEA). FEA is a computational method for solving many types of engineering equations. FEA is particularly well-suited to determining mechanical stress and strain for various loading conditions. This technique is often utilized on shapes too complex to be modeled analytically. We built three-dimensional FE models of individual teeth of Cladodus, Xenacanthus, and Hybodus to visualize stress distribution during puncture, draw, and holding. Teeth were given the material properties of bovine dentine, as those of shark teeth are as yet unknown. Teeth were loaded with 10 kN in three loading regimes: at the cusp apex (puncture), on the lateral edges (unilateral draw), and on the labial and lingual faces (holding struggling prey). Initial results indicate that during puncture, all teeth concentrate stress at the tooth tip as expected, with stress decreasing rapidly with distance from the tip. Furthermore, with increasing penetration into prey, stress would be expected to rapidly dissipate as more of the cusp contacts the prey. During draw events, stress is concentrated at the area where the cusp and base meet for both Cladodus and Hybodus, while Xenacanthus shows stress concentrations at the tooth base. A similar pattern is seen during holding for Hybodus and Cladodus, with additional stress concentrated on the lingual and labial cusp faces for Cladodus. Stress occurs at the lingual and labial cusp faces for Xenacanthus. Despite the fact that broken shark teeth are often found in the fossil record, it is not clear whether damage is taphonomic or occurred in vivo. Regardless, areas of high stress shown in our analyses do not match where breakage occurs, indicating that breakage is most likely taphonomic. The relatively low stresses in these teeth indicate that shark teeth have high safety factors. Flexible attachments may further inhibit stress concentration by distributing stress through the collagenous Sharpeys fibers that anchor the tooth to the dental lamina.