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Re: Avian flight stroke origin



The hoatzins do indeed use a perching grip with their feet.  It's
noteworthy that they seem to adopt a consistent stance (throughout the
photos) in which they are either laying their body across the twig
supporting their weight, or they are hanging from the twig.  The only
video I could find of a young hoatzin climbing showed similar limb and
body positions.

A maniraptor certainly couldn't hang from a branch in the same way.
It is interesting to consider how clawed forelimbs would be employed
with a posture similar to the photo of the turkey that Jason sent.
Gregory S. Paul's Ornitholestes from 1987 comes to mind, albeit with
the caveat that our understanding of forelimb anatomy has changed
since this drawing (seen here:
http://scienceblogs.com/tetrapodzoology/2008/07/history_of_treeclimbing_dinosaurs.php).

Hoatzin primaries also do not get in the way of their claws at very
young ages.  A fully fledged maniraptor would conceivably be
restricted in its grip due to primaries.  Which brings the question,
again, to the ontogeny, morphology and function of the maniraptor
manus.

This is such an intriguing subject and there are so many things we
don't know.  I do appreciate reading these posts and closing some of
the gaps in my own knowledge, by learning from you all.

- Demetrios






On Sun, Aug 14, 2011 at 10:30 AM, Jason Brougham <jaseb@amnh.org> wrote:
>
> I confirm Mr. William's observations that, in Beebe's images of juvenile
> hoatzin, the feet are robust, the hallux is always used to firmly grip
> branches and the forelimbs are often not employed, so that the latter are
> clearly supplemental to the former.
>
> Hoatzins definitely have strong perching feet that Archaeopteryx lacked.
>
>
>
>
> > Demetrios Vital <demetrios.vital@gmail.com> wrote:
> >
> >
> >> Osteologically speaking, does a juvenile hoatzin show a greater
> >> capability for grasping than most maniraptorans?
> >
> >
> > In _Dinosaurs of the Air_, GSP certainly argues that the juvenile
> > hoatzin serves as the best modern analog for how _Archaeopteryx_ might
> > have climbed trees, with the hands and feet both used to "clamber
> > about branches quadrupedally".
> >
> >
> > However, it must be remembered that the pes of the hoatzin is superbly
> > adapted for anisodactyl grasping, with a hallux that is large,
> > reversed, and fully descended.  The hoatzin is, after all, an arboreal
> > bird.  Additionally, hoatzin chicks have extremely large legs and feet
> > in proportion to their body size.
> >
> >
> > There is a nice illustration of a juvenile hoatzin clambering over a
> > branch in Bakker's _The Dinosaur Heresies_ (p.315).  It underscores
> > just how important the big, grasping feet are for climbing.
> > Comparisons between small Mesozoic maniraptorans and modern hoatzin
> > chicks focus on the use of wing-claws in clambering, but often
> > overlook the important role of the perching feet of hoatzins.
> >
> >
> >
> >
> >
> > Cheers
> >
> > Tim
> >
>
>
> Jason Brougham
> Senior Principal Preparator
> Department of Exhibition
> American Museum of Natural History
> 81st Street at Central Park West
> 212 496 3544
> jaseb@amnh.org
>