THE BUZZ SAW SHARK OF LONG AGO: MECHANICS OF THE JAWS AND TOOTH-WHORL OF HELICOPRION DAVISII OR HOW TO EAT WITH A SAW FOR A JAW

The recent reexamination of a tooth-whorl fossil of Helicoprion containing intact jaws shows the location of the symphyseal tooth-whorl on Meckel’s cartilage and positions of fossae associated with the jaw musculature. Here we use that new morphological data to reconstruct the jaw musculature and develop a biomechanical model of the feeding mechanism in these Early Permian predators. The jaw muscles may have generated bite-forces that ranged from 1192N-4732N; however, the mechanics of the jaws and whorl suggest that Helicoprion was better equipped for feeding on soft-bodied prey. Hard shelled prey would tend to slip anteriorly from the closing jaws due to the resistance of the prey tissue, curvature of the tooth-whorl and lack of cuspate teeth on the palatoquadrate. When feeding on soft-bodied prey, deformation of the prey crimps and traps prey tissue between the two halves of the palatoquadrate and the whorl. The curvature of the tooth-whorl and position of the exposed teeth relative to the jaw joint results in tooth functions that differ from anterior to posterior tooth, which aid in feeding on soft-bodied prey. Furthermore, the anterior-posterior facing edges of the teeth facilitate prey cutting with jaw closure and jaw depression. The paths traveled by each tooth during jaw depression are reminiscent of curved pathways used with slashing weaponry such as swords and knifes. Thus, the jaws and tooth-whorl may have formed a multifunctional tool for capturing, processing and transporting prey by cyclic opening and closing of the lower jaw in a sawing fashion.