. Bulletin. Natural history; Natuurlijke historie. 142 PEABODY MUSEUM BULLETIN 42. CMJ Fig. 5L A simple biomechanical analysis of the gape oi Stylinodon mirus using the model of Herring and Herring (1974). In the figure, a and b are the distances of the origin and insertion of the superficial masseter, respectively, from the craniomandibular joint (CMJ) and 0 is the angle between them. The / represents the length of the muscle in closed position and L represents the length of the muscle in L open position when the jaw is rotated through the angle 6. The stretch factor — is the positive square
. Bulletin. Natural history; Natuurlijke historie. 142 PEABODY MUSEUM BULLETIN 42. CMJ Fig. 5L A simple biomechanical analysis of the gape oi Stylinodon mirus using the model of Herring and Herring (1974). In the figure, a and b are the distances of the origin and insertion of the superficial masseter, respectively, from the craniomandibular joint (CMJ) and 0 is the angle between them. The / represents the length of the muscle in closed position and L represents the length of the muscle in L open position when the jaw is rotated through the angle 6. The stretch factor — is the positive square root of: i~ + b^ — lab cosid + 0) a^ + b^ lab cos </) Based on the figure (in arbitrary units), a = , b = , </) = 73 degrees. Thus, if 5 = 50 degrees, L L L - = , if e = 35 degrees, - = , if ^ = 25 degrees, - = groups. The symphysis of the mandible of Stylinodon is extremely heavy and thick as well. This suggests that in Stylinodon the temporalis was responsible for a large component of the side-to-side chewing, and the stresses generated, in part, were responsible for the massive symphysis in Stylinodon. The internally set postglenoid processes could possibly have acted as pivots for a transverse, arclike motion. This may have been a relatively inefficient way to process food, and may have contributed to the eventual extinction of the taeniodonts. All three groups of muscles acting together, but in differing directions, may have helped to keep the jaw from disarticulating. The canines and anterior cheek teeth are greatly enlarged in Stylinodon. These teeth, and the incisors, may have served a crushing/grinding function. Occlusion between the upper and lower canines and P, may also have performed a cutting or slicing scissorlike function. Lastly, the enlarged canines may have, in part, been used in active digging, rooting or some other activity in which the upper canines, in particular, hit an especially hard surface. In several known specimens of
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