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RE: New Ruben Paper



"Femoral-thigh complex," by the authors' terminology, but they really mean
the hip joint is not very mobile. Of course, we knew that ages ago.

What Dann notes is true of *all birds*, not just ratites. And quite
well-demonstrated not only by experimental evidence (Gatesy and others), but
by the simple practice of taking a dead bird and moving its thigh. Lo and
behold, it moves! This happens during walking a small amount, but during
running a larger amount. It is a continuum. Welcome to yet another false
dichotomy.

To be fair, the authors acknowledge this, but then return to the false
dichotomy. From the paper:
" This ''migration'' of the distal femur (probably in response to a
cranially displaced center of mass) is coupled with the thigh's relatively
minor contribution to stride generation during cursorial locomotion
(replaced by substantial contributions from knee and ankle movements). In
kinematic studies of walking guinea fowl, the femur retracted little, only
5-15 compared with 60-80 retraction observed in the vertically oriented
femur of walking alligators, while
the avian knee moved through a 50-70 arc (Gatesy, 1995). Even during running
the femur never passed vertical in birds, achieving a maximal 40 hip
extension relative to the vertebral column (Gatesy, 1995, 1999)."

That's why there are big muscles that act as hip extensors/flexors in birds,
BTW... Stimulate those muscles with a standard muscle stimulator's electric
current, and the femur moves.

Birds do this, theropods do that. Never the twain shall meet... Darwin would
vomit.

Cheers,
John

> -----Original Message-----
> From: Dann Pigdon [mailto:dannj@alphalink.com.au]
> Sent: 10 June 2009 02:11
> To: dinosaur@usc.edu
> Subject: Re: New Ruben Paper
> 
> On Wed, Jun 10th, 2009 at 6:19 AM, Mark Hallett <marksabercat@yahoo.com>
> wrote:
> 
> > As we always say, "wait for the paper", but is Ruben's entire premise
> actually based (on the the
> > implication as I understand it from the SCIENCE DAILY article) that
birds
> have inflexible or only
> > potentially flexible knee joints? This is incorrect.
> 
> Indeed - ostriches (and probably most large ratites) move their femora
> during a fast run, yet I'm
> assuming they're fully capable of breathing at the same time.
> 
> --
> _____________________________________________________________
> 
> Dann Pigdon
> GIS / Archaeologist                Australian Dinosaurs
> Melbourne, Australia               http://home.alphalink.com.au/~dannj
> _____________________________________________________________
> 
> 
>