Is the Shape of Turtle Claws Driven by Locomotor Modes?

Abstract

Claws are the most common attachment mechanism in vertebrates. The comparative anatomy and morphology of claws has been studied mainly in reptiles and birds. However, as far as we know, studies focusing on turtles’ claws are lacking. Turtles occupy a wide range of habitats, from aquatic to terrestrial, and vary in form and behavior, being an ideal model organism for ecomorphological studies. We performed qualitative and quantitative analyses to find a relationship between morphological variation and both ecological factors and phylogenetic constraints that could have driven the evolution of turtles’ claws. The claws of 35 adult turtle and tortoise specimens of 12 species of testudines with different locomotor modes were compared. Our data show several convergence traits in claw shape, with convergence being reinforced by the low phylogenetic signal exhibited by most characters. We propose that claw morphology in turtles is mainly associated with some mechanical functions, such as freshwater-swimming, bottom-walking and tearing of prey.