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Re: Cursorial adaptations (was T.rex and elephants)



Dann Pigdon wrote:

>       This is going back a few years now, so the data is probably
> out of date, but I seem to recall estimates for the top speed of
> some large hadrosaurs to have been greater than that for tyrannosaurs.
> I seem to recall reading this when the Great Russian Dinosaur
> exhibition was having its final showing at Monash Uni here in
> Victoria, Australia. A saurolophus mount was located near to a
> tarbosaurus mount, and I remember the hadrosaur's hind limb bones
> appeared stockier than those of the tyrannosaur. Although the
> tarbosaur's long gracile legs made it "look" faster, I remember
> thinking that the more robust legs of the hadrosaur "looked" better
> able to withstand prolonged stresses from running. These were just
> visual impressions mind you.

You may wish to reread my post from 9/23 or John R. Hutchinson's post from
9/24 and reconsider the implications of robust versus gracile limb
architecture.  In gross generalization, big-boned, heavily muscled animals
are built for power, not speed.  It is far more difficult to quickly swing
a bulky, massive limb than a lightly built limb, particularly if there is
much weight at the distal extremity (the foot and ankle).  Think of the
adaptations and body plans utilized by extant cursorial animals to increase
stride length, stride frequency, and economy of effort.  Bulk up the animal
and the stride frequency and economy of effort decrease.  So I would
<imagine> that the tyrannosaur would have a better figure for top speed
than the duckbill, but I don't know how they would compare in terms of
endurance.

I recall footage of Robert Bakker expounding the virtues of _Tyrannosaurus
rex_ anatomy on the PBS 4 part series, _Dinosaurs!_  He was standing
underneath a mounted _T.rex_ cast (the one John Horner likens to a Rockette
dancer) and pointing at the mighty limb bones which would support a massive
drumstick on this scaled-up roadrunner (as he put it).  In Bakker's view,
the more robust the muscles, the better the speed.  I disagree.  I believe
that the _Tyrannosaurus rex_ design is a compromise between speed and
weight, so I see the big muscles serving instead to fulfill the power
requirements of such a huge and heavy animal.  But, as I've said, there are
also several adaptations present in tyrannosaurs which would presumably
help considerably in terms of speed.  So I hold a view of tyrannosaur
athletic ability that is somewhere between the views of Horner and Bakker
(there's a lot of leeway there)!  I would be interested in any evidence
that duckbills could outpace tyrannosaurs.

To put it in the form of a simple analogy, which is faster, a racehorse or
a plowhorse?  Is not the greyhound -- a very fast dog -- also very gracile?
 Contrast the body type of an olympic weightlifter (built for power)
against the body type of an olympic sprinter.  You get the idea.

Ralph Miller III <gbabcock@best.com>