. Bulletin of the British Museum (Natural History), Geology. THE LIBYAN MIOCENE 505 hyaenodont Hyaenodon mustelinus the angle is also 15° on the carnassial. In both Pterodon and Megistotherium the angle rises to 35° indicating a considerable loss of shearing efficiency. Further the size of the carnassials in Megistotherium is pro- portionately small. None of this suggests that the temporal musculature was developed primarily to operate on the carnassial dentition. Megistotherium has like Crocuta heavy blunt premolars. In Crocuta P^ is used in bone crushing and can exert a pressure of i ton per
. Bulletin of the British Museum (Natural History), Geology. THE LIBYAN MIOCENE 505 hyaenodont Hyaenodon mustelinus the angle is also 15° on the carnassial. In both Pterodon and Megistotherium the angle rises to 35° indicating a considerable loss of shearing efficiency. Further the size of the carnassials in Megistotherium is pro- portionately small. None of this suggests that the temporal musculature was developed primarily to operate on the carnassial dentition. Megistotherium has like Crocuta heavy blunt premolars. In Crocuta P^ is used in bone crushing and can exert a pressure of i ton per cm^; as the tooth crown has an area around 0-5 cm^, this means an effective pressure of about half a ton, which is approximately 2-5 times greater than the pressure man can exert on his back molars. It is not possible to make a precise calculation for Megistotherittm, but is likely that the p3+4 were not less efficient than in Crocuta. The canine of Megistotheritim is unfortunately missing, but the alveolus indicates that it was large, stout and ovoid. The canines from Kenya are exactly the shape and size one would expect for Megistotherium. The efficiency of the canine is dependent on its size and proximity to the fulcrum (glenoid). Hence the facial shortening in hyaena and giant panda improve considerably the efficiency of the canine. (See Table III.) A remarkable feature of Megistotherium is the long face; even with this apparent disadvantage, the ratio of canine area to canine- glenoid length is greater than in any living fissiped. This suggests that the canine is the most important factor in food capture. Smith & Savage (1959) gave an equation for the mechanical efficiency of muscula- ture, T = P X J where T is the force exerted, P is the pull or tension in the muscle, and -7 corresponds to the mechanical advantage of a lever, the ratio of the distance of the applied force from the fulcrum to the distance of the load from the fulcrum (see Fig. 19). In this case
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