How saber-toothed cats used their jaws has been a decades-old debate. Lions today subdue large prey by using a suffocating throat bite, but the spectacularly long upper canines of Smilodon fatalis suggest they use another bite mechanism. We often imagine them using their blade-like canines to ferociously slash their prey, and either eviscerate them or wait for them to bleed out -- but what about the lower jaw? Without an opposing force, the sabertooths likely couldn’t generate enough force to butcher something large. A researcher now proposes a new bite model -- one that works like a can opener. The study was published in PLOS ONE this week.
While jaw function is still hotly debated, researchers currently favor the “canine shear-bite.” That’s when neck muscles called ventral neck flexors assist the mandible in closing the jaws. After biting into the prey with the lower jaws, the neck muscles basically roll the head forward, then downward in a nodding motion to power the bite. However, the mechanical feasibility of this neck-powered biting hasn’t been demonstrated.
Independent researcher Jeffrey Brown manipulated digitized images of a S. fatalis neck and skull and found that rotation of the cranium by the ventral neck flexors wouldn't result in jaw closure. The cranium and mandible end up rotating together, and the jaws remain in an open configuration. Also, with its mouth open wide enough to get its teeth around the prey, the sabertooth's bite forces would be pretty weak.
Brown proposes a new forelimb-powered “Class 1 lever mechanism” for Smilodon jaw function -- which utilizes a motion similar to piercing a can with a can opener, Science reports. But not the modern kind where you turn a handle to rotate a wheel with sharp edges, but the old-timey can opener with a lever handle and a pointed tip, which punches triangular holes in the lid.
In this model (pictured above), the mandible is immobilized against the neck of the prey (like the bottom hook of the can opener), and force from the extension of the forelimbs rotates the head. So when the cat pushes down on the ground with its arms, that increases its leverage by elevating the base of the neck and rotating the head forward (imagine how your hand and arm moves when you puncture a can that way.) Then the long canines pierce and clamp down on the prey’s neck. So, first they bulldog, and then they strike.