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Why fuse the mandibular symphysis? A comparative analysis.
1Department of Anthropology, George Washington University, Washington, DC 20052, and Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA. danlieb@gwu.edu
American Journal of Physical Anthropology
|August 5, 2000
Summary
Symphyseal fusion in mammals is linked to jaw movement during chewing. Species with transverse chewing forces benefit from fused jawbones, enhancing chewing efficiency.
Area of Science:
- Comparative anatomy
- Biomechanics
- Evolutionary biology
Background:
- Mammalian jaw symphyses vary in fusion, impacting mandibular stiffness and strength.
- Fused symphyses offer greater rigidity but can limit independent mandibular motion.
Purpose of the Study:
- To test the hypothesis that occlusal tooth movement orientation drives symphyseal fusion.
- To investigate the relationship between chewing mechanics and the evolution of symphyseal fusion.
Main Methods:
- Comparative analysis of symphyseal and occlusal morphology across mammalian species.
- Kinematic and electromyographic (EMG) analyses of mastication in opossums and goats.
- Comparison with published data on primate chewing patterns.
Main Results:
- A significant correlation exists between symphyseal fusion and occlusal plane orientation.
- Species with more transverse occlusal planes exhibit a tendency towards fused symphyses.
- Independent mandibular rotation and vertical tooth movements characterize species with unfused symphyses.
Conclusions:
- Symphyseal fusion is likely an adaptation to enhance the transfer of transverse occlusal forces.
- Fusion is advantageous in mammals with limited independent mandibular rotation during the power stroke.
- Chewing mechanics, specifically occlusal force direction, are a primary factor in the evolution of symphyseal fusion.