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Re: Speed Potential in Tyrannosaurs (long) [resent plain text]



At 03:18 PM 9/19/2002 +0100, Mike Taylor wrote:
> Date: Wed, 18 Sep 2002 15:05:49 -0700
> From: John R Hutchinson <jrhutch@stanford.edu>
>
> Greg comments that "the belief that increased leg flexion results in
> increased leg muscle mass has yet to be demonstrated by
> measurements, especially of animals of similar size and locomotary
> potential."  I'm not sure what he means here; surely if animals bend
> their legs their muscle mass does not increase, violating the laws
> of energy/mass conservation.  What happens when animals bend their
> legs [...]

Surely what GSP meant by "increased leg flexion results in increased
leg muscle mass" was that animals which habitually adopt a more flexed
stance tend to have proportionally larger leg muscles than their
staighter-legged brethren?  NOT that the act of flexing legs increases
the muscle mass!

Yes, I know, I was just being a bit cagey. :)

So his claim is that this intuitive relation has yet to be
demonstrated by measurements.  Interesting.  True?

It must be true if nothing else changes, but as Biewener and others have noted, other things change in concert with limb orientation. I do think that we need to look at how total limb extensor mass scales in tetrapods; Alexander et al. have provided some preliminary data over the years (esp. late 70s-early 80s) but there is a lot of scatter in those plots, and a broader survey of taxa is needed.


Folks that are interested in this aspect of the controversy _badly_ need to read papers by Andrew Biewener. They are the state of the field, even 12+ years later. The two prime ones are:

Biewener AA. 1989. Scaling body support in mammals: limb posture and muscle mechanics. Science 245: 45-48.

Biewener AA. 1990. Biomechanics of mammalian terrestrial locomotion. Science 250: 1097-1103.

But I would also recommend:

Bertram JEA, Biewener AA. 1988. Bone curvature: sacrificing strength for load predictability? Journal of Theoretical Biology 131: 75-92.

Biewener AA. 1983. Allometry of quadrupedal locomotion: the scaling of duty factor, bone curvature and limb orientation to body size. Journal of Experimental Biology 105: 147-171.

Biewener AA. 1998. Optimization of musculoskeletal design - does symmorphosis apply? In: Weibel ER, Taylor CR, Bolis L, eds. Principles of Animal Design : The Optimization and Symmophosis Debate. Cambridge, UK: Cambridge University Press, 70-77.

Biewener AA, Bertram JEA. 1991. Efficiency and optimization in the design of skeletal support systems. In: Blake RW, ed. Efficiency and Economy in Animal Physiology. Cambridge, UK: Cambridge University Press, 65-82.

And references therein. The refs that Pauls' post cited are also worth looking over, as is any work by R.McNeill Alexander and colleagues.


--John R Hutchinson