Size, Shape, and Stress in Tortoise Shell Evolution

Abstract

Abstract: Testudinid turtles, comprising a single family with a fairly uniform shell morphology but a wide range of body sizes, present a unique opportunity for testing hypotheses regarding the evolution of shell size, shape, and functional performance. Here, we apply geometric morphometric methods and finite element models to test two hypotheses regarding the coevolution of size, shape, and mechanical performance (shell strength). First, we predicted that larger turtles will tend to have shell shapes distinct from those of smaller turtles. Second, we predicted that the shell shapes (independent of size) of smaller turtles will be stronger than those of larger turtles to compensate for the reduction in strength that accompanies a decrease in size. We used multivariate phylogenetic comparative methods to assess the significance of the relationship between shell size and shell shape, and used finite element analysis to assess the mechanical behavior of tortoise shells. We detected a relationship between she...