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Fig. 5. Time sequence of photographs from video of the underwater corkscrewing motion of a Pacific striped dolphin (Lagenorhynchus obliquidens). The corkscrewing motion is characterized by a balance of the anterior drive torque at the pectoral flippers and the posterior drive torque produced at the flukes. Any anterior-posterior imbalance would generate a systematic, continual torsion of the anterior half with respect to the posterior half (Dynamic Balance Condition 2). This torsion would be indicated by a helical twisting in the dorsal/ventral line

of coloration discontinuity. This sequence of images of the corkscrewing dolphin shows no discernable torsion in the body. This orientation demonstrates the balance in torques that the animal achieves in order to execute corkscrewing motion at a uniform rotational rate. A uniform rate of rotation around the longitudinal axis itself is indicative of a balance of resistive torques and drive torques (Dynamic Balance Condition 1). Image 6 shows the dorsal fin canted due to the resistive torque in rotational motion.

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