Re: four winged Archaeopteryx

[Michael Mortimer <mickey_mortimer111@msn.com>]

Richard Cowen wrote-

> The rigid furcula makes sustained flight difficult, but it doesn't  prevent 
> flight as far as I  can imagine. So I concede that one to  David 
> Marjanovic. The flexing of the furcula acts to facilitate  respiratory 
> pumping, so helps to provide the fuel-burning capacity  that powers 
> sustained flight.

I don't follow the biomechanical/physiological side of things much, but has 
this been suggested before-
Is it possible the furcula took over the gastralia's role?  Claessens (2004) 
suggested a ventilatory role for gastralia, and these are well developed in 
basal birds with robust furculae (archaeopterygids, jeholornithids, 
Sapeornis, confuciusornithids).  Enantiornithine-grade birds have thinner 
furculae which nonetheless may have had limited flexibility due to their 
U-shaped cross section, and reduced gastralia.  Once modern furculae evolve 
around the Yixianornis level, gastralia are reduced in size and number, and 
disappear by the time Gansus branches off.

Mickey Mortimer