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

[John R Hutchinson <jrhutch@stanford.edu>]

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