Quadrupedal and Bipedal Locomotion of Lizards

SINCE the appearance of previous work on the bipedal running of Basiliscus basiliscus (Snyder, 1949), the motion picture analysis method of studying locomotion has been applied to several species of lizards. High speed motion pictures were taken of Amphibolurus cristatus (Agamidae), Crotaphytus c. collaris, Gambelia w. wizlizenii and Sceloporus u. undulatus (Iguanidae), and Cnemidophorus t. tessellatus (Teiidae). Quadrupedal locomotion of all species was photographed as well as the bipedal running characteristic of Amphibolurus, Crotaphytus and Gambelia. Motion picture photography of running lizards presents several problems. Standard motion picture cameras operating at a maximum speed of 64 frames per second are inadequate to cope with the rapid leg action of the animals and when separate frames are projected for analysis, detail is greatly obscured, particularly in regard to position of the feet. Consequently, photography was done with an Eastman Kodak 16 mm. High Speed Camera equipped with a Kodak Anastigmat 63 mm. f/2.7 lens. Fifty-foot spools of Cine-Kodak Super X panchromatic reversal film were used exclusively. Since it was necessary to provide at least a three-foot running area, and since the high camera speed requires intense illumination, nine reflector photospot lamps were mounted to cover the running track about two feet from the sand on which the lizards ran. It was necessary to place a sheet of heavy, heat absorbing glass between the lights and the running track; otherwise the sand rapidly became too hot for the lizards to tolerate. With this lighting arrangement good results were obtained with a camera speed of between 1000 and 1500 frames per second (exposure time per frame between 1/5000 and 1/5500 second), a speed adequate to fix leg and foot motion completely. Tests made at higher speeds resulted in underexposure. Increasing the illumination by concentrating three or more photospots at any one point solved the underexposure problem but created a new one; the lizards would not perform in such brilliant light. The basic factors influencing the gaits of quadrupedal mammals as well as descriptions of the types of gaits employed have been clearly set forth by Howell (1944) and his assumption that the speed gait of lizards is the trot has been verified by the present studies. The description of quadrupedal locomotion to follow applies basically to all of the five species studied. The action of a hind leg illustrates the basic pattern of movement for all four appendages. The propulsive stroke begins when the foot strikes the ground, at which time the foot and shank are extended and the