ABSTRACT
Softshell Turtles ....................................................................................................... 157 6.4 Future Directions for Studies of Turtle Locomotion .......................................................... 157 Acknowledgments .......................................................................................................................... 159 References ...................................................................................................................................... 159
Turtles possess one of the most distinctive body plans among vertebrates (Burke, 1989). The presence of a bony shell in turtles affords them physical protection from a wide range of predators and environmental hazards, providing opportunities for turtles to use distinctive life history and survival strategies (Cagle, 1950; Jayes & Alexander, 1980; Gibbons, 1990; Jackson, 2000, 2002, 2004; Ultsch, 2006). However, in addition to the benefits that they convey, the shells of turtles also place unusual constraints on their locomotor systems. Because the carapace of the shell is fused to the dorsal vertebrae, the body axis of turtles is inflexible except for the neck and tail (Zangerl, 1969;
Ernst et al., 1994). Although the tail plays an important role in the locomotion of many vertebrates (Snyder, 1962; Fish, 1984; Gatesy, 1990; Lauder, 2000), in almost all extant turtles the tail is highly reduced and thus contributes little to the production of locomotor forces (Zug, 1971; Walker, 1973; Pace et al., 2001; Willey & Blob, 2004). As a result, turtles must rely exclusively on movements of the limbs to propel themselves (Gillis & Blob, 2001; Pace et al., 2001; Rivera et al., 2006).
