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, they are mainly comprised of densely packed collagenous fibers. A structural analysis was performed to determine the internal structure and orientation of these fibers. Fluke specimens from common dolphins (Delphinus delphis), bottlenose dolphins (Tursiops truncatus), and harbor porpoises (Phocoena phocoena) were obtained from stranding centers. Dissection of the flukes distinguished two distinct fibrous layers. The inner layer (thick layer) originated from the leading edge and was found to contain thin fibers angled with respect to the chordwise axis that displayed greater flexibility along the chordwise axis and less flexibility along the spanwise axis. The outer layer (thin layer) originated from the tail stock and was found to contain thick fibers angled along the spanwise axis of the fluke that displayed flexibility opposite to the manner of the thick layer. The arrangement of the fibers gave the flukes anisotropic properties. The two-dimensional orientation of the fibers within the fibrous layers was determined using 1.5mm slices which were oriented in the chordwise direction and examined with a stereomicroscope under polarized light. Fibers in the thick layer in the parasagittal plane displayed a crisscross arrangement with fibers oriented at an average of either 70° or 111° in relation to the chord line. Fibers in the thin layer were found to be oriented in the same direction on a one-fiber-thick plane. The two fibrous layers constitute the main structural support for the cetacean fluke. The differences in flexibility, fiber orientation, and thickness help the flukes to maintain their shape while being flexible during swimming.
