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Re: Fw: Dinosaurs and birds
Perfect. Thanks for the ref. Yes, it seems to me that 'synchronicity' of the
fore-limbs must come first (before the flight-stroke), although in my personal
model synchronicity has it's origins in semi-aquatic locomotion rather than
predation. If you watch children running in shallow (mid-thigh or deeper)
water, I think you might notice they naturally tend to use the hands in
synchronous fashion as they assist the legs by 'pulling ' at the waters
surface... they seem to alternate between an alternating stroke and synchronous
stroke, the synchronous stroke coming into play when the water is deeper, or
when they tire.
So, my personal cartoon involves a bipedal predator in a semi-aquatic
environment, and a shallow water column frequently choked w/ aquatic
vegetation. I think of it as the 'Gollum' model.
----- Original Message ----
From: Tim Williams <firstname.lastname@example.org>
Sent: Wednesday, April 4, 2007 8:45:36 PM
Subject: RE: Fw: Dinosaurs and birds
Don Ohmes wrote:
>And to change the subject slightly-- has anybody formally proposed a
>specific scenario/environment >for the establishment of synchronous use of
>the forelimbs, as opposed to an alternating pattern? >Isn't that necessary
>to start all this anatomical sophistication in motion?
I'm not sure I'm answering your question correctly (so apologies in
advance)... The "Predatory Stroke" hypothesis (Gauthier and Padian, 1985),
for example, proposes that synchronous motion of the forelimbs actually
preceded the evolution of the avian flight stroke. Under this hypothesis,
the maniraptoran ancestors of birds are thought to have captured prey using
both forelimbs at once; and the anatomy of the joints allowed both the
forelimbs to be extended rapidly toward the prey. In fact, this hypothesis
proposes that the prey-catching motion of the forelimbs (the "predatory
stroke") is biomechanically homologous to the avian flight stroke, with a
I hope that helps.
Gauthier, J. A., and Padian, K. (1985). Phylogenetic, functional, and
aerodynamic analyses of the origin of birds and their flight. In: M. K.
Hecht, J. H. Ostrom, G. Viohl, and P. Wellnhofer, (eds). The beginnings of
birds: proceedings of the international _Archaeopteryx_ conference,
Eichstätt 1984. Freunde des Jura-Museums, Eichstatt, Germany. p.185-197.
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