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doing computer simulations of locomotion right
Hutchinson's preference for discussing my criticisms of his work on tyrannos
in the formal literature is reasonable, and it will be interesting to see
what is presented - I'm waiting to see the papers before I put together my
tome on the subject.
Concerning the recent comments on attempts to restore the locomotion of
extinct creatures it should be understood that I do not oppose all computer
simulation work, only that which produces spurious results far out of line
with observed reality in actual animals.
For a paper that appears to to a good job of modeling the real world see
Sellars W et al. 03 Predicting the metabolic energy costs of bipedalism using
evolutionary robotics. J Experimental Biology 206:1127-36. It's cool stuff,
in which they use advanced technigues including Darwinian genetic algorithms
to model locomotion in people. Best of all the results produced muscle mass
and power requirements close to those really present in humans. This is
unlike H&G's Nature paper in which the actual muscle energetics of large
animals were ignored. It also shows that not only is it possible to publish a
study that has passed the test of successfully passing the crucial test of
replicating the muscle power output test of appropriate living subjects, that
it is not legitimate to fail to do so.
Other points -
The evolutionary techniques used by Sellars et al better mimic those of
nature than standard biomechanics, and are potentially more effective than
the latter in which people program a computer with what they have concluded
is correct (but may be errant).
At the same time the new paper exposes how much still remains poorly
understood about animal locomotion, casting caution on overinterpreting the
results of biomechanics research.
Some of the contents of Sellars et al. hint at how natural selection has
adapted animals in ways that minimize power needs in large animals by means
that have escaped standard biomechanics work.
Hopefully this method will be applied to ostriches, rhinos, elephants and so
forth to see if it generates results that are compatible with actual muscle
mass and power in these organisms. Then extend them to tyrannosaurs and other
It will also be interesting to see if the method can solve certain problems.
For example the biggest tyrannosaurs could not straighten their knees more
than 120 degrees without disarticulating the lateral condyle and making the
knee prone to total dislocation. At the same time flexed knees are a basic
running adaptation, and tyrannosaurs had the muscle power needed to run fast.
Since limb flexion supposedly dramatically increases muscle mass and power
requirements (but actual data in normally locomoting animals contradict
this), this situation has given biomechanical studies fits. So the question
is how are animals running around on flexed legs without paying a penalty in
terms of extra muscle mass and work. Since evolution solved the problem, can
evolutionary simulations do the same?
One of the problems I've had with digital simulations is how those who do
them, after all that work, often get over enthusiastic about the results and
promote them despite a lack of confluence with what has been observed about
animal locomotion. It's just so enticing seeing something on a computer
screen, it seems real. Combine that with the intuitive belief that big
animals must be slow and it is a potent combination. So far no one has been
able to show where my conclusions on power requirements in running giants are
in error, yet a number of bright people just do not accept the results
because it's not within their big animals must be slow worldview.