Mechanical function of the unique alveolar torus in the sabretooth <i>Nimravus brachyops</i> (Nimravidae, Carnivora).

Abstract

Sabretoothed mammals exemplify some of the most extreme craniodental morphological specializations in vertebrates. Much attention has been devoted to their elongated upper canines; however, not all sabretooths possess the same complex of morphological characteristics associated with sabres, making generalization of the requirements for specialized jaw function difficult. Here, we test the approximately 150-year-old hypothesis that a unique jaw torus seen in a single sabretooth genus, <i>Nimravus</i>, is an adaptation to resist biting forces. We tested a suite of biting scenarios using finite element analysis and found that the inclusion of a torus structure decreased the performance of the mandible in its stiffness and strain resistance but increased simulated bite force as well as efficiency. The presence of a torus also preferentially improved the overall performance of the mandible at higher gape angles, configurations often inferred for sabretooths. Lastly, a potential novel torus-associated portion of the masseter muscle would have further increased bite performance. The strong association between morphology and performance suggests that the torus may have played a mechanical role in mastication, and its apparent unique evolution is another prime example of mosaic evolution in the sabretooth functional morphology.