[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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

----- 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,


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...