Meeting Abstract

51.5  Saturday, Jan. 5  Shell Game: Coevolution and Compromise in Four Functions of the Turtle Shell STAYTON, C. Tristan; Bucknell University tstayton@bucknell.edu

The turtle shell (composed of a dorsal carapace and ventral plastron) acts in many biologically important roles. Most obviously, it serves to protect the turtle within from predation and thus acts as a load-bearing or force-resisting structure. It serves, along with the protruding parts of the turtle�s body, to exchange heat with the environment. During aquatic locomotion, it produces drag on the swimming turtle and may even serve as a hydrofoil. Finally, it presents an obstacle to righting in turtles that have been overturned. The degree to which the shell performs each of these functions is highly dependent on shell shape. Here, I summarize variation in the shape of the shell by a geometric morphometrics assessment of all the major clades (Families) of turtles. I then use Finite Element methods to evaluate the effect of this variation on each of the four functions mentioned above. Differences between terrestrial, freshwater, and marine turtles are discussed, along with the mechanical implications of those shape differences. Some shell shapes are optimal for multiple functions, but none is optimal for every function. Thus the evolution of turtle shell shape often involves compromise; different functions are optimized depending on the species� environment or method of locomotion.