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Re: a little background



> Date: Thu, 28 Feb 2002 12:39:07 -0800
> From: John R Hutchinson <jrhutch@stanford.edu>
>
>          Sorry about the long post previously; I hope people are not
> responding by attaching the whole text without cutting+pasting.
> Here is another long post.  Don't worry, I will shut up soon enough.
> :)

John,

Please NEVER apologise for long and interesting posts on this list!
It's been excellent on here in the last few days: controversial paper,
lots of discussion, and -- best of all -- the author on hand to
explain where we're all missing the point!  Many thanks for taking the
time.

>          Anyway, I always found Greg and others' arguments about
> fast tyrannosaurs very interesting, and at times convincing.  Greg
> has made the best (by far) arguments for fast-running tyrannosaurs,
> ever.

... and we need to find a way to make them true again :-)
[Beauty is truth and truth beauty, and running Tyrannosaurs are
beautiful, right?]

What intrigues me most is the idea of applying your methodology to
more extant species, so we can get a better idea of how well it
applies across the board.  Useful as the chicken and 'gator analyses
are, the straight line through two points seem to be a perfect fit :-)
(Just as I am really looking forward to Parrish & Stevens' new
dinomorph work which, as I understand it, aims to validate their
models of sauropod cervical anatomy by applying the same methods to
the necks of camels, giraffes etc.)

Specifically, I would be fascinated to see how ostriches come out.
(I've not read all of
http://tam.cornell.edu/students/garcia/.trex_www/naturepaper.html
yet, but a swift grep for "ostrich" reveals nothing.)  From my totally
uninformed perspective, based on little more than looking at ostriches
in zoos, it seems to me that they have amazingly little in the way of
leg muscle, at least in the distal 3/4 of the leg -- yet they are
among the fastest of all terrestial animals.  Have you, by the
slightest chance, informally put an ostrich in your machine and
cranked the handle?

One more comment on ostriches, provoked in part by Tom's comment:

> Date: Fri, 1 Mar 2002 08:52:24 -0500
> From: "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>
> 
> One of the basic points coming out of various lines of research is
> that the mechanical world that 3 or 4 or 6 or more tonne animals
> live in is very different from the world that 100 kg or 500 kg or
> maybe even 1 tonne animals live in.

[Disclaimer: I am not a Real Scientist.  I am a computer scientist,
which is really a branch of art.  So I might be talking complete
nonsense.  Sorry if I am.]

Anyway -- just as the dynamics of insect flight are fundamentally
different from those of bird flight (dominated more by friction drag
than form drag), so I found myself wondering whether large theropods
might run in a fundamentally different way from BSBSs (Boring Small
Bipeds :-) like chickens.

BSBs run by pushing themselves forward with each step; but one can
imagine a larger animal, with more momentum (and proportionally less
drag effects to worry about) running by essentially falling forwards
all the time, and controlling that fall by taking steps that do not
need to propel the body, but merely get the leg forwards quickly
enough to stop the fall becoming terminal.  Then the primary force
that the leg needs to absorb is the slight downward movement of the
body mass at the end of each step, pushing upwards to turn that into
the slight upward movement necessary for the ILB to make it over the
crown of the next step.  Purely intuitively, it seems that this would
require substantially less muscle mass than the BRB running style.
Yes?  No?

Then it occurred to me that a while back when I saw film of an ostrich
running, it seemed to be doing something very similar to that: at
least, it _appeared_ (though all those fluffy feathers might by hiding
the truth) that its centre of mass was _well_ forward of its feet as
it ran.  So that seems an extra reason to be interested in how well
ostriches fit your body-mass/leg-muscle-mass graph.

A final though.  If large theropods did run in a falling-forward
style, that has implications for manoeuverability.  There wouldn't
have been any :-) Seriously, an animal running in that way would find
it much harder to turn quickly, I imagine -- and might have had
trouble stopping, except perhaps by crashing into a prey animal.  Not
sure what the ecological consequences of this would be, but it does
suggest that a quadruped running from a _rex_ might do well to turn
suddenly (well, more suddenly than the _rex_ can) and charge it.

OK, my rambling ends.  If this is all a load of uninformed nonsense
then sorry for wasting your time; but if some of it is uninformed
non-nonsense, then great!

Thanks again not only for writing the paper, but for discussing it
out here where we laymen lurk, along with the Real Dino Guys.

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor   <mike@miketaylor.org.uk>   www.miketaylor.org.uk
)_v__/\  "I have always prided myself on being in a field that has
         no practical application" -- Palaeontologist James Farlow.