Re: Fw: Dinosaurs and birds

[don ohmes <d_ohmes@yahoo.com>]

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.

Don

----- Original Message ----
From: Tim Williams <twilliams_alpha@hotmail.com>
To: dinosaur@usc.edu
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 
few modifications.

I hope that helps.

Reference:

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.


Cheers

Tim

_________________________________________________________________
MSN is giving away a trip to Vegas to see Elton John.  Enter to win today. 
http://msnconcertcontest.com?icid-nceltontagline