Meeting Abstract
50.8 Jan. 6 Death roll of the alligator: mechanics of a new twist on an old spin FISH, F.E.*; BOSTIC, S.A.; NICASTRO, A.J.; BENESKI, J.T.; West Chester University; West Chester University; West Chester University; West Chester University ffish@wcupa.edu
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 hind limbs were appressed against the body and the head and tail were canted to the longitudinal body axis. With respect to the body axis, the head and tail were bent at 49.2o and 103.3o, respectively. The head, body and tail rotated smoothly and freely around their individual axes of symmetry at 1.6 Hz. In order to visualize, test and evaluate variation in individual components of the death roll sequence, we constructed and animated a 3-D model. The simulated death roll allowed us to alter viewing angles and kinematic parameters to match those observed and measured in recorded sequences as well as isolate individual parameters for further testing. 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 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 0.012 N. Shear force was calculated to scale with body length to the 4.2 power. When scaled up to a 3 m alligator, shear force was calculated at 134 N. The death roll augments the limitations of the feeding morphology of the alligator. Shear forces generated by the spinning maneuver increase disproportional with alligator size, allowing dismemberment of large prey.
