Smilodon fatalis Bite Mechanisms: New Functional Considerations in Jaw and Articular Disk Reconstruction

Abstract

Smilodon fatalis is among the most iconic of fossil sabertooths, best known for elongated canine teeth that enabled it to kill large prey. S. fatalis reconstructions published over the last 150 years (as well as many natural history exhibits) are typically modeled after living large conical tooth cat anatomy because there are no living sabertooths. Dental and correlated musculoskeletal differences between the living and extinct cats with the two different dentition types have led to misinterpretations of the appearance and gape capabilities of Smilodon. Historically, the way in which the S. fatalis skull and mandible soft tissues have been reconstructed does not take into account the bite angles that are the most useful for a living cat. Specifically, the angle at which the mandible and maxilla can move in relation to one another must also account for the effect generated by the muscles and tendons that limit jaw opening and closing. The usual reconstructed display shows a mandible that could not open sufficiently to allow a gape wide enough to encompass the diameter of a chicken's egg. The jaw joint is often oriented so that it would not generate much bite force, as it sometimes is positioned to look as though it is dangling uselessly. The articular disk has been ignored. In this study, we are testing hypotheses related to the typically depicted canine tooth positions and the lack of inclusion of soft tissue influences such as the articular disk that is usually present in the craniomandibular joint. By reconstructing the size, shape, thickness, and then inserting an articular disk, the jaw then lines up correctly, and a bite force can be more accurately calculated. We tried several different methods of estimating the size of the articular disk using paper, leather, felt, and silicone until we found one that allowed the mandible and maxilla to line up precisely. This works to solve the two common issues; computer-based studies that modeled the amount of bite force in S. fatalis with a few showing a powerful bite and secondly, canines are often mounted so far out of their alveoli that the S-shaped dentine margin is exposed. Exposed dentine and jaw misalignment would be very painful to a living animal and would decrease the mechanical advantage of the upper canines. When the upper canine alveoli are not maximally filled, the teeth are less securely anchored. By seating the upper canines properly S. fatalis could use these teeth with a decreased likelihood of breakage from the bite forces generated. S. fatalis evolved with long slender bladelike canines. This tooth configuration would be especially susceptible to breakage from large bending moments and torque. To use these teeth effectively, the bite needs to be in line with the anteroposterior axis of the head and aimed toward the jugular groove of the neck of prey, with minimal side-to-side movement. Anchoring the canines securely in their alveoli helps eliminate this problem. Our data shows that revisioning the S. fatalism skull gives a more accurate picture of the way this cat lived, killed its large prey, and our new data allows for scientists recalculate bite forces.