Re: Senter 2006, Confuciusornis, and humeral mobility

["Jason Brougham" <jaseb@amnh.org>]

> keep in mind that we have to get it into steady
> flight, first.

I'm pretty confident now that we've got it. The humeral head is so wide,
with a minor axis (drawn from the glenoid across the widest part of the
humeral head) set at something like a 45 degree angle from the shaft that
I am confident that, through rotation alone, the trochlea could be
elevated at least 25 degrees above the glenoid, probably a lot more. With
that, and such a  low wing loading, and extant volant birds that have
comparable stroke amplitudes, I see no impediments to steady flight.

Perhaps this twisting of the humerus is what Wang, Nudds and Dyke hinted
at as "very different... aerial locomtion", although such humeral twisting
does take place in extant, volant, birds to differing degrees.


> The "it can't take off on its own card" gets played
> A LOT for various kind of birds, and for most of them, it's bunk.

Yes, it's more a matter of difficulty, isn't it? I've read that there are
all different strategies, such as heading into gusts of wind, that birds
use to reduce their exertion, but this is not an absolute limit on their
abilities.

> Note that in order to perform WAIR up a tree, a bird actually needs quite
> an advanced upstroke and the ability to build a negative lift coefficient.

Right, and, of course, Shearwaters can definitely elevate the humerus a
great deal. In the film, at the 30 second marker, a shot begins where we
are looking up at the birds and over their backs. Their humeri elevate to
about 45 degrees, and Confuciusornis may not have been capable of that.
Other times, in the less steep stretches, they are just scratching up with
their toes.

Also, we must all recall, Confuciusornis could have scaled trees with its
huge, recurved, and sharp thumb and third finger talons. This is an extra
option in the tool kit that Shearwaters do not enjoy.

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