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

[Mike Habib <habib@jhmi.edu>]

> >
> It IS easier to become airborne from an elevated position and you  
> can also travel much further. Even if theropod could jump really  
> high, it would still only be falling from a few feet, which would  
> only give it a tiny fraction of the air time it would get from  
> jumping out of a 50 foot tree. Plus after jumping it would  
> immediately begin to slow down, and in the end it would have been  
> better off simply running.

Ah, and it returns.  This came up in another recent discussion, which  
sadly became rather more heated than it ought to have been.  In any  
case, I suggest being careful with the term "easy" in this context.   
It does, indeed, take less power to drop from a height (assuming you  
are already there), than to leap from a substrate.  However, what is  
"easy" in terms of biological systems depends entirely on the  
ancestral state.  Birds inherited highly powerful hindlimbs from their  
ancestors, which were mechanically capable of powering leaping  
launches.  This doesn't mean that the origin of flight in birds was  
purely cursorial in nature, but it does indicate that an arboreal  
stage isn't mechanically required.

Incidentally, the airspeed in leaping launches is generated from the  
leap, not a subsequent fall from the top of the jump.  It is also  
worth noting that arboreal birds tend to launch by leaping from the  
elevated substrate, so arboreal launches are probably only rarely  
simple "falls".  There is also the issue of the phylogenetic timing of  
the power stroke versus the timing and pace of airfoil evolution - a  
great deal depends on how these features map relative to each other in  
the phylogeny.


> > No, the intermediary stage proceeding flight DOES NOT have to be  
> > gliding. It might have been; but this cannot be assumed.
>
> I think it does, simply because there has to be a transition between  
> a simple fall and powered flight, and gliding is much less energy  
> consuming than flapping your wings to achieve what is basically a  
> prolonged fall. Yes I guess an animal could flap its wings to  
> prolong its fall, but why waste the energy when it could achieve the  
> same thing by evolving a larger wing surface to simply glide.

A fall to flapping transition is only one of the possible array of  
transitions.  What consumes the most energy is actually rather  
complicated, since the climbing costs have to be included, but in any  
case, biological transitions don't always follow a low-energy path.   
The flapping stroke might have evolved secondary to airfoil expansion,  
but it also could precede airfoil expansion or evolve in synchrony.

Cheers,

--Mike


> >

Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280-0181
habib@jhmi.edu