There is another mechanism besides muscle that gives energy to running and hopping animals. It enables such animals as kangaroos to run faster than their muscles alone can take them. What happens is the tendons act as springs that stretch and then snap back. There is no reason to think that a large and heavy dinosaur couldn’t make use of such a tendon-spring mechanism to go a high speed, although not for long.
In a recent reply to a letter about the
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Sue being lame and her survival being attributed to group care, Gordon M. Burghardt responded that all of these behaviors have been observed in living “reptiles” (See letter appended to “Turn Your Head and Roar,” SN: 12/15/01, p. 376:
Turn Your Head and Roar
.). My understanding was that dinosaurs had been concluded to be the precursors of birds, not reptiles. This would seem to apply to the question of how fast tyrannosaurs ran, as well. If they were built like a bird, then maybe they weren’t as massive as the researchers think.
Your article reports that
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couldn’t run, but “Dinosaur tracks show walking and running” (SN: 2/23/02, p. 125: Available to subscribers at
Dinosaur tracks show walking and running
.) shows that
, a comparable animal of comparable size, both walked and ran. It would seem that something’s amiss. What if
“only” ran at half of what some paleontologists have estimated, 72 kilometers per hour, and probably only for short bursts? It would most likely have developed only enough speed to catch its prey, and I doubt it ever needed 72 km/hour for that purpose.
In fact, the largest tyrannosaurs were about 4 meters longer than
and probably weighed about 5 times as much.
‘s walking speed was a large fraction of
‘ running pace primarily because the larger animal had a longer stride.
One letter, above, suggests the possibility of energy storage in elastic tendons. I would like to offer a quick reply. While it is true that elastic energy storage can play a role in the running gaits of various animals (including humans), our analysis is unchanged by its presence. The force in question is transmitted through the muscle and tendon in series and would be essentially independent of tendon stiffness. Our calculations were based on the necessary muscle force and limiting stress, not the necessary energy input. Elastic energy storage would make the animal more efficient, but it would not allow the muscles to withstand significantly higher leg forces.