Fig. 3 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 3. Comparison of 2D side-view and fully 3D definitions of parameters for the bifulcral model of mandibular leverage, shown using Didelphis marsupialis Linnaeus, 1758 as an example. A. Left side-view of mandible in closed gape position, showing the locations of the working-side condylar fulcrum green) and bite point fulcrum (blue). The example temporalis force vector (red) drives rotation about both of these fulcra, and produces output force vectors that are tangential to circles centered on their respective fulcra (dashed arcs). B. Oblique lingual view showing important points and lever arms corresponding to the working-side medial pterygoid force (MP-W; shown as a red arrow) using a fully three-dimensional model of bifulcral mandibular leverage. The very medially directed line-of-action for the medial pterygoid demonstrates the large differences in orientation between the condylar plane (CP; shown with a green transparent plane), bite plane (BP; shown with a blue transparent plane), and a parasagittal (side-view) plane. The three-dimensional bifulcral model calculates bite forces and joint forces by projecting load points into their respective planes, as distances perpendicular to these projections do not affect leverage calculations. Definition of numbered points: 1, mesial postcanine point (PM); 2, distal postcanine point (PD); 3, centroid of insertion area for working-side medial pterygoid (MP-W); 4, centroid of origin surface for MP-W on skull; 5, location of working-side joint (WJ); 6, projection of WJ into BP; 7, projection of an example bite vertex on the third lower molar into the CP. Abbreviations: BF, bite force; ILBP-W, in-lever of the bite plane on the working-side; ILCP-W, in-lever of the condylar plane on the working-side; JF-W, joint force on the working-side; MP-W, medial pterygoid working-side; OLBP-W, out-lever of the bite plane on the working-side; OLCP-W, out-lever of the condylar plane on the working-side. Not to scale.