Mechanical function of the unique alveolar torus in the sabretooth Nimravus brachyops (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, Nimravus, 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.