Re: implications of Microraptor and bird flight origins

[DinoBoyGraphics@aol.com]

I don't have much time, I just wanted to respond to a few things that Tom Holtz 
and Greg Paul said.  I've been previously unaware of any claims that the 
hemoral heads of sinornithosaurs were spherical, I'll have to look into that.  
Certainly would be good evidence of adaptation to an arboreal lifestyle.   I'd 
point out that the new specimen in Nature is not preserved spread eagle, and 
the sigle specimen (Dave) may or may not be a statistical anomalie.  I agree 
with GSP that there is no reason to assume a priori that new (or any) 
dromaeosaurs are further from moderns bird than Arcaheopteryx is.   On the 
other hand, with the growing data set, I would expect that at a certain point 
that a cladistic analysis will catch the major reversals to flightlessness, if 
indeed they did happen.
    Despite the quality (and cahrisma!) of his research, I'm not convinced that 
Dial's paper explains the origins of aerodynamic surfaces, though it may well 
explain the transition to flight and/or an arboreal lifestyle.  Which brings me 
to another problem.   The aquisition of aerodynamic controls, even if aquired 
totally in a terrestrial context, would probably make it much easier to invade 
arboreal niches, confounding our ability to interpret the ancestral conditionin 
the fossil record.  On the other hand, it's equally plausible that the 
development aerodynamic surfaces evolved in an arboreal context could be 
exapted for the terrestrial ballistic phase hunting style of derived 
dromaeosaurs.
    What disturbs me about all these lines of discussion on the list (my 
apologies to Marius if I misunderstood his post), is that there are few 
falsifiable predictions being made.  With heaps of due respect to XU et al, I 
think most of the evidence they used to support the arboreal origin of avian 
flight is essentially ad hoc.   The only exception is their claim that the leg 
feathers would interfere with terrestrial locomotion, which I disagree with for 
the reasons given in my previous post.

More later...

Scott Hartman
University of Wyoming
(307) 265-1045