Meeting Abstract
Limb bone morphology often correlates with functional demands placed on animals by the environment. Recent studies of limb bone allometry that compared functionally divergent turtle taxa showed that highly specialized lineages like sea turtles exhibit extensive flattening of the humerus that contributes to the development of flipper-shaped forelimbs, allowing for lift-based swimming (i.e. underwater flight). In addition, terrestrial tortoises showed more robust humeri and femora, potentially reflecting specializations for resisting high torsional loads during terrestrial walking and digging behaviors. However, whether such morphological distinctions might be found within clades that encompass species with diverse ecological habits has not been tested. Emydid turtles represent such a clade, with both semi-aquatic and fully terrestrial representatives. To test whether limb bone size and shape varies among closely related taxa with divergent ecological habits, we assessed scaling patterns and overall morphology of the humerus and femur of 23 turtle species representing four emydid genera: Graptemys (semi-aquatic), Pseudemys (semi-aquatic), Trachemys (semi-aquatic), and Terrapene (terrestrial). Our analyses indicate that in general, emydid taxa scale isometrically for most length-diameter and length-mass relationships. However, interestingly, Graptemys exhibit long and robust humeri (relative to body mass), as well as femora that are long relative to body mass. The robust forelimbs of Graptemys might provide advantages in handling robust, shelled food items attached to the substrate, such as mussels and gastropods, or assist as the turtles pull themselves out of the flowing water to bask.
