QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online August 9, 2007
Journal of Experimental Biology 210, 2811-2818 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004267

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JEB Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fish, F. E. Articles by Beneski, J. T. Search for Related Content PubMed PubMed Citation Articles by Fish, F. E. Articles by Beneski, J. T.

Death roll of the alligator: mechanics of twist feeding in water

Frank E. Fish^1,*, Sandra A. Bostic¹, Anthony J. Nicastro² and John T. Beneski¹

¹ Department of Biology, West Chester University, West Chester, PA 19383, USA
² Department of Physics, West Chester University, West Chester, PA 19383, USA

View larger version (65K): [in this window] [in a new window]   Fig. 1. Juvenile alligator showing tail restraint. The wooden stick on the dorsum of the alligator is 180 mm in length.

View larger version (104K): [in this window] [in a new window]   Fig. 2. Initiation (0 ms) of the spinning maneuver. The alligator first bends into a C-shape and then appresses its limbs against the body.

View larger version (178K): [in this window] [in a new window]   Fig. 3. Spinning maneuver of juvenile alligator after initiation (0 ms). The alligator has bitten onto a piece of meat. During the spinning maneuver, the rotational axes of the head, body and tail maintain a fixed relative orientation to the frame of reference of the aquarium. Note that the relative orientation of the body parts do change with respect to each other. For instance, the tail starts bent to the left side of the alligator at 20 ms, but is bent to the right side of the animal by 120 ms, although still on the left side of the image. The limbs are appressed against the body and the head and tail are canted at angles to the body axis. The head, body and tail all spin in the same rotational direction with the same angular speed.

View larger version (9K): [in this window] [in a new window]   Fig. 4. Angular displacement of head and tail to symmetry axis of body in relation to spin rate. Solid lines indicate mean angles for the head and tail.

View larger version (15K): [in this window] [in a new window]   Fig. 5. Model of alligator during spinning maneuver. The head and tail are modeled as ellipsoids with circular cross sections. The tail is modeled as a elongate right circular cone. The semi major (a) and semi minor (b) axes of ellipsoids are exemplified on the body. Angular displacements of the head () and tail () are shown relative to the symmetry axis of the body. Angular velocities (H, B, T) of body parts rotate together. The local Cartesian coordinate system is illustrated along the symmetry axis for each body part. The roll axis (RR') is indicated by the broken line at a distance (d) from the symmetry axis of the body. The angular velocity (rev) around the roll axis is opposite in direction to the angular velocities of the body parts. The inset illustrates the vector angular momenta for the entire system. The vector sum of the angular momenta is zero for the motions of the alligator during the spinning maneuver.

View larger version (20K): [in this window] [in a new window]   Fig. 6. Schematic of spinning motions. Blue arrows indicate directions of rotation of head, body and tail segments. Red arrows indicate compensatory rotation of the entire system. The relative size of the arrows illustrates a reduced rate of rotation of the compensatory spin compared to the rotation rates of the head, body and tail segments.

View larger version (5K): [in this window] [in a new window]   Fig. 7. Scaling relationship between the mass and length of 51 alligators. Data were collected from individuals used in this study and from other sources (McIlhenny, 1935; Joanen and McNease, 1971; Dodson, 1975; Fish, 1984; Erickson et al., 2003). The dotted line shows the regression line (Eqn 15 in text), which was significant (R=0.99; P<0.001).

View larger version (9K): [in this window] [in a new window]   Fig. 8. Calculated shear force as a function of total length of alligators. The lines for shear force were based on Eqn 17 for a combination of rotation rates (rotations s–1) and body lengths.