A New Model of Feeding Biomechanics Based on Tied-Arch Principles

Understanding of how skulls transmit and resolve forces during biting currently derives from several independent frameworks originating mostly from carnivorans and primates. This new biomechanical model integrates this classic jaw lever theory with structural mechanics to explain how the highest magnitude stresses and strains arise through the tetrapod cranium during biting. The model proposes that bite forces are resolved through compression-dominant arcs spanning the skull between jaw muscle origins, biting teeth, and jaw joints. The apex, or "vertex," of a compression arc corresponds to the most efficient load-bearing geometry for resisting the muscle resultant force vector. Finite element simulations of a dietary generalist (Didelphis virginiana), a bone-cracking specialist (Sarcophilus harrisii), and an encephalized primate (Cacajao calvus), combined with novel visualization of subsurface stresses, demonstrate that withstanding high bite-induced reaction forces benefits from skull geometries that optimize compressive load paths while minimizing peak tensile stresses. Skull functions that impede generation of continuous compression arcs, such as enlarged braincase size, increase reliance on more diffuse stresses and tensile support. By contrast, when selection favors resisting higher bite reaction forces, bone structure is predicted to evolve toward funicular shapes, thereby consolidating compressive stress fields. However, geometry will always be constrained by development, phylogenetic history, and functional trade-offs that can impact the continuity or efficiency of compressive resolution. Compression arcs are therefore often supported by tensile ties, thus framing the tetrapod skull as a tied-arch bridge analog. The model provides a first-principles framework for predicting and interpreting evolutionary optimization in skull structure and biting performance.