A structural and functional analysis of walking in the turtle, Chrysemys picta marginata

Walking of Chrysemys has been studied by cinephotography and x‐rays. The lateral sequence, diagonal couplet gait, limb support sequence, and wide track provide great stability, yet a slight pitch and roll cause some plastral drag. Velocity ranges from 28 mm to 51 mm/second, and fluctuates within a stride. Limb movements and structure resemble those of other ectotherms, but incorporate modifications reflecting the animal's short, broad trunk encased in a shell and carried close to the ground. The triradiate pectoral girdle so articulates with the shell as to act as a truss for weight transfer to the ground. Girdle rotation increases the efficiency of the girdle as a truss, and contributes to locomotor efficiency. The glenoid cavities are more than twice as far apart as the acetabula, so a thrust from the pectoral girdle has less propulsive efficiency on the center of gravity than one from the acetabulum. The humerus and femur are protracted to a greater extent than in other ectotherms and their horizontal arcs of retraction are less. Rotation of these elements about their longitudinal axes contributes to the length of a stride and to foot placement and withdrawal. Differences in the movements of comparable segments of front and hind limbs correlate with differences in the width of the girdles, a crus longer than the antebrachium, and different capacities for joint rotation.