Meeting Abstract
P2.71 Wednesday, Jan. 5 Functional morphology of the perivertebral muscles in great apes – Are humans unique ? SCHILLING, Nadja*; HESSE, Bettina; NEUFUSS, Johanna; THORPE, Susannah K.S.; Friedrich-Schiller-University Jena, Germany; Friedrich-Schiller-University Jena, Germany; Friedrich-Schiller-University Jena, Germany; University of Birmingham, UK nadja.schilling@uni-jena.de
Humans are unique among primates in having a striding bipedal gait and a permanent orthograde trunk posture. Thus, the functional demands on the human trunk musculature are different from those in other great apes. To 1) increase our understanding of the functional morphology of the axial system in great apes, 2) distinguish adaptations to human bipedalism from characteristics shared with other great apes due to their common phylogenetic history, and 3) reconstruct functional transformations of the axial musculature during ape evolution, we investigated the lower thoracic and lumbar perivertebral muscles of the orangutan and chimpanzee regarding their fiber type composition and anatomical cross-sectional area (ACSA) and compared these data with results from humans. Muscle fiber type distribution was determined using immunohistochemistry; ACSA was measured in CT scans. Similar to humans, chimpanzees and orangutans did not show the segregation of specific fiber types typical for other mammals. This striking reorganization facilitates all muscles to equally contribute to trunk mobilization and stabilization. Furthermore, our results show that compared to the chimpanzee and human, which were fairly similar in the slow fiber proportion, orangutans showed overall higher proportions of slow fibers; likely related to their slow, cautious locomotor behavior. Non-human great apes have a relatively small lateral epaxial muscle tract compared to their body mass, while all other perivertebral muscles have the ACSAs as predicted by body mass. This smaller lateral tract points to a decreased need for mobilization, likely correlated with the comparatively short, stiff trunk of non-human apes.
