Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

[David Marjanovic <david.marjanovic@gmx.at>]

----- Original Message -----
From: "Sim Koning" <simkoning@msn.com>
Sent: Friday, September 26, 2008 8:22 AM

> I don't think it's too level, since there are plenty of flightless highly 
> cursorial birds that have almost completely lost their wings and completly 
> lost their flight feathers. This seems to indicate to me that wings don't 
> help much when it comes to running.

Agreed. Wings are more likely for brooding and/or the less falsifiable 
display.

> If anything, modern cursorial animals seem to be going away from flight,

Yes...

> while arboreal animals are going towards it.

No. None shows any hint of a transition from gliding to flapping.

Some have doubted whether such a transition is even possible, arguing that 
incipient flapping would lose to an increase in drag and decrease in lift in 
a glider. Sure, the bats come very clearly from the trees, so gliding is 
almost the default option for what their unknown ancestors did, the extent 
of bat wing membranes is certainly compatible with a gliding ancestry --  
maybe their wingstroke comes from some kind of grasping behavior, catching 
insects in mid-air with their hands?
       I'll have to take another look at the hindlimbs of *Onychonycteris* 
to see if there's any hint of a jumping ancestry.

While I am at it, it is also commonly assumed that the previous step is a 
transition from parachuting to gliding, but whether such a thing has ever 
happened or is even possible is another question that has occasionally been 
asked in the literature. Animals that descend at an angle of, or anywhere 
near, 45° seem to be rare or nonexistent; instead, parachuters go down 
nearly vertically, while gliders move almost horizontally. Given the fact 
that parachuting requires maximizing drag while gliding requires minimizing 
drag, an animal in between might combine the worst of both worlds. IMHO it 
is more parsimonious to assume that parachuting evolved from jumping down 
from a tree, while gliding evolved from jumping from branch to branch.

One argument against a gliding ancestry for birds is almost never mentioned: 
the tertials. In a glider we'd expect the wing to stretch from the tip of 
the forelimb all the way to the body wall. But in birds the wing feathers 
are attached to the hand and the forearm only; they curve around the elbow, 
but that still leaves a gap along the upper arm. In extant birds, at least, 
this gap is filled by the tertials, extra-long contour feathers that grow 
from the upper arm and AFAIK the sides of the body; tertials are not wing 
feathers. I can't see how this is compatible with bird wings having evolved 
for gliding. (It fits brooding, though.)
       In comes Scott Hartman and says *Archaeopteryx* lacked even 
tertials...