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Re: Various thoughts re: implictions of _Microraptor_ and bird flight origins



In a message dated 1/24/03 5:27:12 AM Pacific Standard Time, 
tholtz@geol.umd.edu writes:

<< B) In my view, Dial's discovery demolishes the split between "ground up" 
and
 "trees down": it shows that people have been talking at cross-purposes.
 Despite what people have been arguing for years, this isn't an "either/or"
 situation, but might better be explained as two different steps in bird
 flight origins, with Dial's Wing-Assisted Incline Running (WAIR) as the
 functional missing link between the two. >>

Actually, it demolishes the "strict ground-up" theory, in which flight is 
purported to evolve in ground-dwelling dinosaurs with >no< arboreal component 
in their lifestyle, through an accumulation of flight-related characteristics 
each of which appeared for a non-flight reason (such as predation) and was 
exapted for flight by the organism once it acquired enough of them to fly. 
This was the prevailing theory among "birds are dinosaur descendant" workers 
until the small, feathered, and obviously arboreal theropods were found at 
Liaoning. Thereafter they started to back-pedal. Just search the archives of 
dino list for the mid-to-late 1990s and you'll find enough posts to 
demonstrate this.

WAIR behavior would have been available to Permian prolacertiforms, among 
which are a number of winged gliding forms as well as the ancestors of the 
pterosaurs (a la Peters) and the archosaurs (a la me and many other workers). 
We haven't found exactly the right ancestral prolacertiforms yet, but they 
could turn up at any time.