Abstract The tetrapod water–land transition has been studied for more than a century, but questions about the locomotor function of early tetrapod limbs still remain. The limb and girdle skeletons of stem tetrapods are morphologically distinct from those of crown tetrapods, probably resulting in differences in range of motion and muscle leverage. To test hypotheses about their limb function, we built three‐dimensional musculoskeletal models of the stem tetrapods Acanthostega (Devonian) and Pederpes (Carboniferous), and of an extant salamander and lizard for comparison. We predicted that the joints of stem tetrapods would not be able to accommodate the full range of movements used by extant tetrapods during terrestrial walking, and that stem tetrapods would have less muscle leverage for resisting vertical forces and for hindlimb‐based propulsion. As expected, hip and shoulder mobility in the two stem tetrapods was incompatible with the kinematic patterns used by extant sprawling tetrapods. In contrast, their hip and shoulder depression muscle moment arms were similar to or greater than those of the crown tetrapods, and retraction moment arms were similar between the hip and shoulder in all four tetrapods, showing little evidence that the limbs of stem tetrapods were less adapted for weight support or HL‐driven locomotion. However, the moment arm results were sensitive to methodological choices such as joint angles and normalization. Comparison with additional extinct and extant tetrapods with different locomotor strategies could clarify how muscle moment arms are related to limb mechanics and aquatic versus terrestrial locomotion.
Molnár et al. (Sun,) studied this question.