Meeting Abstract
Cookiecutter sharks (Isistius spp.) possess particularly unique feeding mechanisms, behaviors, and ecological niches. Their semi-circular, scoop-shaped lower jaw bears a row of teeth fused into a saw blade, which is used to excise circular flesh plugs from large fishes or cetaceans by engaging the teeth and then rotating the body about its longitudinal axis. The extent to which the constituents of this mechanism facilitate their unique feeding behavior and ecology has not been quantitatively examined. Therefore, we examined the effects of their semi-circular jaw morphology and fused tooth-blade on the structural performance of the jaws. Lower jaw models of I. brasiliensis and I. plutodus were reconstructed from CT scans and Finite Element Analysis was used to quantify stress and strain energy density in jaws with a) fused tooth rows, b) unfused tooth rows (i.e., teeth digitally separated), and c) no teeth. Forces were applied to the jaws to simulate normal biting (i.e., forces perpendicular to the jaw occlusal surface) and rotational biting (i.e., forces parallel to the jaw occlusal surface). Modeling scenarios were also applied to the spiny dogfish Squalus acanthias to determine if the modified cookie cutter shark feeding mechanism facilitates rotational feeding behavior relative to the basal condition for squaliform sharks. Preliminary analyses indicate that lower jaws perform better (i.e., lower stress, strain energy density) during rotational biting, and that the presence of both functional and replacement tooth rows improves structural performance. These results suggest that jaw geometry and dental reinforcement facilitate the unique rotational feeding behavior of cookie cutter sharks.
