Meeting Abstract
During swimming, cetaceans generate hydrodynamic thrust with dorso-ventral oscillations of flexible tail flukes. These flukes do not contain rigid skeletal structures. Instead, the majority of the fluke is composed of a densely packed collagenous matrix with collagen fibers running in a crisscrossing pattern along the chordwise axis. Flukes from six species of odontocete cetaceans were examined to compare the morphology and orientation of fibers in relation to the physical properties of the flukes. All species were found to have the same generalized morphology, but the pygmy sperm whale (Kogia breviceps) was found to have additional fibers running perpendicular along the span of the fluke. Compression tests were performed at 10%, 40%, and 70% of the span on the flukes of each species in three orientations: spanwise, chordwise, and dorso-ventral. In all species, the spanwise direction was found to be the most rigid, while the chordwise and dorso-ventral directions were found to be more pliable. Anisotropic deformation of the fluke samples always occurred in the spanwise direction when compressed in either the chordwise or dorso-ventral directions, and very little deformation was observed when the fluke samples were compressed in the spanwise direction. These results are consistent with the three-dimensional structure of the flukes that were comprised of two-dimensional sheets of material aligned tightly in a plywood-like configuration along the span of the flukes. The anisotropic properties imparted by this unique internal structure help the flukes to maintain their spanwise rigidity while allowing partial flexibility during swimming.
