Studies into the function of structures are crucial for making connections between morphology and behaviour of organisms, but are still rare for the terrestrial Testudinidae. We investigated the kinematics of shoulder girdle and forelimb motion in Hermann's tortoise Testudo hermanni by using biplanar X-ray fluoroscopy with a two-fold aim: firstly, to understand how the derived shapes of shoulder girdle and carapace together influence rotation of the girdle and, secondly, how girdle rotation affects forelimb excursion. The total degree of shoulder rotation in the horizontal plane is similar to a species with a less domed shell, but due to the long and nearly vertically-oriented scapular prong, shoulder girdle rotation contributes more than a third to the horizontal arc of the humerus and nearly 40 percent to the rotational component of step length. The antebrachium and manus, which act as a functional unit, contribute to roughly fifty percent to this component of the step length due to their large excursion almost parallel to the mid-sagittal plane. This large excursion is the result of the complex interplay between humerus long-axis rotation, counter-rotation of the antebrachium, and elbow flexion and extension. A significant proportion of forelimb step length results from body translation due to the propulsive effect of the other limbs during their stance phases. Traits that are similar to other tortoises and terrestrial or semi-aquatic turtles are the overall slow walk due to a low stride frequency, and the lateral-sequence, diagonally-coupled footfall pattern with high duty factors. Intraspecific variation of carapace shape and shoulder girdle dimensions has a corresponding effect on forelimb kinematics.
- Received January 1, 2016.
- Accepted June 20, 2016.
- © 2016. Published by The Company of Biologists Ltd