| Summary: | The cetacean tail fluke blades are not supported by any vertebral elements. Instead, the majority of the blades are composed of a densely packed collagenous fiber matrix known as the core layer. Fluke blades from six species of odontocete cetaceans were examined to compare the morphology and orientation of fibers at different locations along the spanwise and chordwise fluke blade axes. The general fiber morphology was consistent with a three‐dimensional structure comprised of two‐dimensional sheets of fibers aligned tightly in a laminated configuration along the spanwise axis. The laminated configuration of the fluke blades helps to maintain spanwise rigidity while allowing partial flexibility during swimming. When viewing the chordwise sectional face at the leading edge and mid‐chord regions, fibers displayed a crossing pattern. This configuration relates to bending and structural support of the fluke blade. The trailing edge core was found to have parallel fibers arranged more dorso‐ventrally. The fiber morphology of the fluke blades was dorso‐ventrally symmetrical and similar in all species except the pygmy sperm whale (Kogia breviceps), which was found to have additional core layer fiber bundles running along the span of the fluke blade. These additional fibers may increase stiffness of the structure by resisting tension along their long spanwise axis. Delphinus delphis Mid-Span Slices Delphinus delphis Tail Base Slices Delphinus delphis Tail Tip Slices Grampus griseus Mid-Span Slices Grampus griseus Tail Base Slices Grampus griseus Tail Tip Slices Kogia breviceps Mid-Span Slices Kogia breviceps Tail Base Slices Kogia breviceps Tail Tip Slices Lagenorhynchus albirostris Mid-Span Slices Lagenorhynchus albirostris Tail Base Slices Lagenorhynchus albirostris Tail Tip Slices Phocoena phocoena Mid-Span Slices Phocoena phocoena Tail Base Slices Phocoena phocoena Tail Tip Slices Tursiops truncatus Mid-Span Slices Tursiops truncatus Tail Base Slices Tursiops truncatus Tail Tip Slices
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