SUMMARY Crocodilians, including the alligator (Alligator mississippiensis), perform a spinning maneuver to subdue and dismember prey. The spinning maneuver, which is referred to as the `death roll',involves rapid rotation about the longitudinal axis of the body. High-speed videos were taken of juvenile alligators (mean length=0.29 m) performing death rolls in water after biting onto a pliable target. Spinning was initiated after the fore- and hindlimbs were appressed against the body and the head and tail were canted with respect to the longitudinal body axis. With respect to the body axis, the head and tail bending averaged 49.2° and 103.3°,respectively. The head, body and tail rotated smoothly and freely around their individual axes of symmetry at 1.6 Hz. To understand the dynamics of the death roll, we mathematically modeled the system. The maneuver results purely from conservation of angular momentum and is explained as a zero angular momentum turn. The model permits the calculation of relevant dynamical parameters. From the model, the shear force, which was generated at the snout by the juvenile alligators, was 0.015 N. Shear force was calculated to scale with body length to the 4.24 power and with mass to the 1.31 power. When scaled up to a 3 m alligator, shear force was calculated at 138 N. The death roll appears to help circumvent the feeding morphology of the alligator. Shear forces generated by the spinning maneuver are predicted to increase disproportionately with alligator size, allowing dismemberment of large prey.

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The flukes of cetaceans function in the hydrodynamic generation of forces for thrust, stability, and maneuverability. The three-dimensional geometry of flukes is associated with production of lift and drag. Data on fluke geometry were collected from 19 cetacean specimens representing eight odontocete genera (Delphinus, Globicephala, Grampus, Kogia, Lagenorhynchus, Phocoena, Stenella, Tursiops). Flukes were imaged as 1 mm thickness cross-sections using X-ray computer-assisted tomography. Fluke shapes were characterized quantitatively by dimensions of the chord, maximum thickness, and position of maximum thickness from the leading edge. Sections were symmetrical about the chordline and had a rounded leading edge and highly tapered trailing edge. The thickness ratio (maximum thickness/chord) among species increased from insertion on the tailstock to a maximum at 20% of span and then decreasing steadily to the tip. Thickness ratio ranged from 0.139 to 0.232. These low values indicate reduced drag while moving at high speed. The position of maximum thickness from the leading edge remained constant over the fluke span at an average for all species of 0.285 chord. The displacement of the maximum thickness reduces the tendency of the flow to separate from the fluke surface, potentially affecting stall patterns. Similarly, the relatively large leading edge radius allows greater lift generation and delays stall. Computational analysis of fluke profiles at 50% of span showed that flukes were generally comparable or better for lift generation than engineered foils. Tursiops had the highest lift coefficients, which were superior to engineered foils by 12-19%. Variation in the structure of cetacean flukes reflects different hydrodynamic characteristics that could influence swimming performance. Anat Rec, 290:614-623, 2007Rec, 290:614-623, . 2007 Wiley-Liss, Inc.

The flukes are the primary locomotor structure in cetaceans, which produce hydrodynamic thrust as the caudal vertebrae are oscillated dorso-ventrally. Effective thrust generation is a function of the kinematics of the flukes, the angle of attack between the flukes and the incident water flow, and the shape of the flukes. We investigated the effect of bending within the caudal region of odontocete cetaceans to determine how changes in angular displacement between caudal vertebrae could effect passive shape change of the flukes. The internal and external changes of bent flukes were examined with computer tomography. Flukes and tailstock were removed from deceased Delphinus delphis, Lagenorhynchus acutus, Peponocephala electra, Phocoena phocoena and Tursiops truncatus, and bent on an adjustable support at 0, 45 and 90 degrees . At 0 degrees , cross-sections of the flukes displayed a symmetrical profile. Cross-sections of bent flukes (45 degrees , 90 degrees ) were asymmetrical and showed a cambered profile. Maximum cambering occurred close to the tailstock and decreased toward the fluke tip. Maximum angular displacement occurred at the 'ball vertebra', which was located posterior of the anterior insertion of the flukes on the tailstock. Bending at the 'ball vertebra' passively cambers the flexible flukes. Cambering could increase hydrodynamic force production during swimming, particularly during direction reversal in the oscillatory cycle.

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