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THE UNIVERSITY OF CALGARY Eric Snively A ... - Ohio University

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Alexander et al. (1 979) rewrded a duty factor $=0.29 at a stride frequency of 2.3<br />

Hz.<br />

Such a low duty factw seems unrealistic for G. libratus, a much larger biped<br />

than the ostrich. With legs roughly twice as long as those of an ostrich, the<br />

tyrannosaurid could conceivably reach fairly high absolute speeds without<br />

recourse to a long ballistic suspended phase. Carrano (1998) and Christiansen<br />

(1 999) hypothesized that large theropods were unlikely to have employed long<br />

suspended phases. These would require the inducement of high potential<br />

energies, leading to high (and potentially damaging) bending force about<br />

secondary moments when the foot retumed to the ground.<br />

These authors did not consider how energy storage by elastic tissues would<br />

decrease the rate of strain on bone and distribute footfaIl energies (see<br />

Discussion below). Nevertheless, the high number of unknown factors<br />

introduced by tendon elasticity, as well as consideration of bone strength<br />

(Christiansen 1999), signal caution in ascnbing long ballistic periads to Iarge<br />

theropods. A conservatively high duty factor, p=0.45, is therefore estimated for a<br />

nrnning Gorgosaurus libratus.<br />

b. Forces with the metatarsus normal to the substrate:<br />

Substituting these quantities into equation (6): m=2212 kg, g=9.81<br />

rneterdsec?, p=0.45, gives the resulting ground-reaction force FG:<br />

(7) FG=37873 N

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