Meeting Abstract
The evolution of hindlimb bone morphology, muscle attachments, and joint geometry in the tetrapod lineage tells a story of adaptation to the environment through structural modification. We compared the pelvic appendages of three stem tetrapods and closely related fish spanning the fin-limb transition (Eusthenopteron, Acanthostega, and Pederpes) with two extant lobe-finned fish and two extant tetrapods using musculoskeletal modeling. We estimated osteological range of motion of the hip and knee joints and mapped muscles onto the skeletons based on osteological correlates of muscle attachment from the literature and plotted the leverage of individual muscles over a range of motion. Similar to prior reports on forelimb evolution, a “bottleneck” in range of motion, particularly long-axis rotation, coincided with the origin of tetrapods. We also observed a trend towards increased leverage of hip depressors and retractors in tetrapods – potentially reflecting a shift to limb-driven locomotion – which was especially noticeable in post-Devonian taxa. In contrast, the fish had greater leverage for elevation and depression than any other type of movement. These results help to refine our understanding of how the roles of how the roles of the forelimb and hindlimb changed as tetrapods increasingly adopted a more terrestrial way of life, as well as the evolution of structure-function relationships over macroevolutionary timescales.
