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Re: "Cursoriality", etc.
> In some ways is it actually easier to maintain a high speed as size
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.