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Re: "Cursoriality", etc.



GSP1954@aol.com wrote:
> 
> In some ways is it actually easier to maintain a high speed as size
> increases. 

Maintain, yes.

Achieve, no.

It takes more energy, more muscle power, to accelerate than to maintain
a given speed, does it not?  Maybe a hadrosaur could cruise all day at
25mph, but how long would it take that hadrosaur to _reach_ 25mph? 
Maybe a tyrannosaur could sustain 30mph for a week, but how long a run
in open country would it need to reach 30mph?  You're talking about
accelerating six or seven tons of meat and bone, after all.  That's a
lot of mass, and it will take a lot of energy and time to accelerate.   

Then there's the issue of musculature.  If a tyrannosaur had musculature
like a cheetah -- HIGH energy output for a short time -- it wasn't going
to get going very fast.  A cheetah can sustain its super-high energy
output for ten or twenty seconds, enough to carry it to a speed of over
100kph and a distance of half a kilometer or so.  How fast could a
tyrannosaur go if it could only sustain high energy output for thirty
seconds?  Especially considering that anatomy notwithstanding, there are
mechanical limits to how fast a leg can be physically picked up, swung
forward, and put back down.  

Also, concerning these compraisons of dinosaurs to rhinos and
titanotheres: doesn't it make sense that you may not be able to
reasonably compare two-footed animals and four-footed animals? 
Four-footed animals have a variety of gaits to choose from: the basic
walk, trot, canter, gallop, plus specialized gaits like the pace and
amble.  Each works differently, and is best used at a different speed. 
Bipedal animals have _one_ basic gait, and the only way to change speed
is to change stride length and frequency.  Granted that a biped doesn't
have to worry about legs on the same side getting tangled up, but OTOH
there's only two "drive legs" too, and each leg has to carry a larger
portion of the mass and produce a larger portion of the forward thrust.
 
-- JSW