WHITENACK, L.B.; MOTTA, P.J.; KOOB, T.J.; University of South Florida; University of South Florida; Shriners Hospital for Children, Tampa: A preliminary analysis of selachian tooth performance

Feeding performance plays an important role in overall fitness. An organism must be able to capture prey to grow, survive, and reproduce. Tooth morphology contributes to feeding performance, and this component has largely been ignored in studies on functional morphology of chondrichthyan feeding. The goal of this study is to explore the evolution of selachian teeth in the context of functional morphology. Here we report the results of preliminary performance testing of selachian teeth during puncture. Teeth from a variety of lamniforms, carcharhiniforms, and one hexanchid shark were individually mounted on steel rods and driven through food items at a rate of 400 mm/s using a MTS 858 MiniBionix II universal testing system. Prey items were attached to a 5 kN load cell. Force and pressure at initial penetration, maximum force, and elastic modulus were analyzed. The largest maximum penetration force (49.08 N) was for an upper anterior tooth of Carcharhinus leucas, occurring after the cross-sectional area of the tooth abruptly increases, proximal to the distal notch. During unidirectional draw, maximum force is lower (24.27 N) than that of puncture, indicating this serrated, broadly triangular tooth morphology may be better suited for draw, as seen in lateral head shaking. The distal notch of many broadly triangular teeth is hypothesized to increase stress for shearing fibrous connective tissue. In comparison, Isurus oxyrinchus, which has narrower non-serrated teeth, required 17.03 N for puncture and 23.53 N for unidirectional draw, indicating that this tooth morphology is better suited for puncture. These results have implications for studies of fossil chondrichthyans, where typically tooth morphology is used to predict feeding ecology in the absence of performance data.